Tektronix ADA400A Service and user manual

Instruction Manual

ADA400A
Differential Preamplifier

070-9164-01

Warning

The servicing instructions are for use by qualified
personnel only. To avoid personal injury, do not
perform any servicing unless you are qualified to
do so. Refer to the Safety Summary prior to
performing service.

Copyright © T ektronix, Inc. All rights reserved.
T ektronix products are covered by U.S. and foreign patents, issued and pending. Information in this publication supercedes

that in all previously published material. Specifications and price change privileges reserved.
T ektronix, Inc., P.O. Box 500, Beaverton, OR 97077
TEKTRONIX and TEK are registered trademarks of T ektronix, Inc.

WARRANTY

T ektronix warrants that this product will be free from defects in materials and workmanship for a period of three (3) years
from the date of shipment. If any such product proves defective during this warranty period, T ektronix, at its option, either
will repair the defective product without charge for parts and labor, or will provide a replacement in exchange for the
defective product.

In order to obtain service under this warranty, Customer must notify Tektronix of the defect before the expiration of the
warranty period and make suitable arrangements for the performance of service. Customer shall be responsible for
packaging and shipping the defective product to the service center designated by T ektronix, with shipping charges prepaid.
T ektronix shall pay for the return of the product to Customer if the shipment is to a location within the country in which the
T ektronix service center is located. Customer shall be responsible for paying all shipping charges, duties, taxes, and any
other charges for products returned to any other locations.

This warranty shall not apply to any defect, failure or damage caused by improper use or improper or inadequate
maintenance and care. T ektronix shall not be obligated to furnish service under this warranty a) to repair damage resulting
from attempts by personnel other than T ektronix representatives to install, repair or service the product; b) to repair
damage resulting from improper use or connection to incompatible equipment; or c) to service a product that has been
modified or integrated with other products when the effect of such modification or integration increases the time or
difficulty of servicing the product.

THIS WARRANTY IS GIVEN BY TEKTRONIX WITH RESPECT TO THIS PRODUCT IN LIEU OF ANY
OTHER WARRANTIES, EXPRESSED OR IMPLIED. TEKTRONIX AND ITS VENDORS DISCLAIM ANY
IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
TEKTRONIX’ RESPONSIBILITY TO REPAIR OR REPLACE DEFECTIVE PRODUCTS IS THE SOLE AND
EXCLUSIVE REMEDY PROVIDED TO THE CUST OMER FOR BREACH OF THIS WARRANTY. TEKTRONIX
AND ITS VENDORS WILL NOT BE LIABLE FOR ANY INDIRECT , SPECIAL, INCIDENTAL, OR
CONSEQUENTIAL DAMAGES IRRESPECTIVE OF WHETHER TEKTRONIX OR THE VENDOR HAS
ADVANCE NOTICE OF THE POSSIBILITY OF SUCH DAMAGES.

Table of Contents

General Safety Summary iii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Getting Started 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Product Description 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Accessories 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Installation 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Functional Check 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Operating Basics 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Determining the Effective Volts/Division 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Reference 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Connecting the Inputs 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Setting the Controls 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Tips for Reducing Signal Interference 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Specifications 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Nominal Characteristics 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

W arranted Characteristics 22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

T ypical Characteristics 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Performance Verification 29. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Requirements for Performance 29. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Equipment Required 29. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Procedures 30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Adjustment Procedures 37. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Requirements for Performance 37. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Equipment Required 37. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Procedure 38. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Maintenance 47. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Warranty Service 47. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Preparation 47. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cleaning 48. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Replacement Procedures 48. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Replacement Parts 52. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Theory of Operation 52. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Troubleshooting 54. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Repackaging Instructions 54. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Replaceable Parts 55. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Parts Ordering Information 55. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Using the Replaceable Parts List 56. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Glossary 61. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Index 63. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ADA400A Differential Preamplifier

i

Contents

List of Figures

Figure 1: Configuration Jumper for Scale Factor Coding 3. . . . . . . . . . . . . . . . . .

Figure 2: Front Panel Controls 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 3: Input Connectors and Fuses 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 4: Output Connector 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 5: Selecting the Input Impedance 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 6: Differential Rejection of Common-Mode Signal 14. . . . . . . . . . . . . . . . .

Figure 7: Eliminating Ground Loops in a Differential Setup 15. . . . . . . . . . . . . . .

Figure 8: Input and Offset Range for X 0.1 Gain 17. . . . . . . . . . . . . . . . . . . . . . . .

Figure 9: Input and Offset Range for X 1 Gain 17. . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 10: Input and Offset Range for X 10 Gain 17. . . . . . . . . . . . . . . . . . . . . . . .

Figure 11: Input and Offset Range for X 100 Gain 18. . . . . . . . . . . . . . . . . . . . . . .

Figure 12: Typical DC and AC Coupled CMRR in X0.1 Gain 26. . . . . . . . . . . . . .

Figure 13: Typical AC and DC Coupled CMRR in X1 Gain 27. . . . . . . . . . . . . . . .

Figure 14: Typical and Warranted CMRR in X10 Gain 27. . . . . . . . . . . . . . . . . . . .

Figure 15: T ypical and Warranted CMRR in X100 Gain 28. . . . . . . . . . . . . . . . . . .

Figure 16: Location of Adjustments Underneath Inner Shield 39. . . . . . . . . . . . . .

Figure 17: Replacing TEKPROBE Interface Pins 49. . . . . . . . . . . . . . . . . . . . . . . .

Figure 18: Replacing the TEKPROBE collar 49. . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 19: Input Connectors and Fuses 50. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 20: Potentiometer Connections 51. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 21: Diagram of the ADA400A Differential Preamplifier 52. . . . . . . . . . . . .

Figure 22: ADA400A Differential Preamplifier — Exploded View 59. . . . . . . . . .

List of Tables

Table 1: Gain settings 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

T able 2: Controls, Connectors, and Indicators 9. . . . . . . . . . . . . . . . . . . . . . . . . .

T able 3: Effective Volts Per Division Settings 10. . . . . . . . . . . . . . . . . . . . . . . . . .

T able 4: Nominal Characteristics — Signal Acquisition System 21. . . . . . . . . . . .

T able 5: Warranted Characteristics — Signal Acquisition System 22. . . . . . . . . . .

T able 6: Warranted Characteristics — Environmental 23. . . . . . . . . . . . . . . . . . . .

T able 7: Typical Characteristics — Signal Acquisition System 24. . . . . . . . . . . . .

T able 8: Typical Characteristics — Mechanical Characteristics 26. . . . . . . . . . . . .

T able 9: Test Equipment 29. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

T able 10: Equipment Settings for Gain Checks 31. . . . . . . . . . . . . . . . . . . . . . . . .

T able 11: Equipment Settings for X100, 100 kHz CMRR Checks 33. . . . . . . . . . .

T able 12: Equipment Settings for X100, 10 kHz CMRR Checks 34. . . . . . . . . . . .

T able 13: Equipment Settings for X100, 100 Hz CMRR Checks 35. . . . . . . . . . . .

T able 14: Equipment Settings for X10, 100 kHz CMRR Checks 35. . . . . . . . . . . .

T able 15: Equipment Settings for X10, 10 kHz CMRR Checks 36. . . . . . . . . . . . .

T able 16: Equipment Settings for X10, 100 Hz CMRR Checks 36. . . . . . . . . . . . .

T able 17: Equipment Settings for Gain Adjustments 40. . . . . . . . . . . . . . . . . . . . .

T able 18: Equipment Settings for Offset Adjustments 41. . . . . . . . . . . . . . . . . . . .

T able 19: Equipment Settings for Attenuator Balance Adjustments 42. . . . . . . . .

T able 20: Equipment Settings for CMRR Adjustments 43. . . . . . . . . . . . . . . . . . .

T able 21: Equipment Settings for LF Adjustments 45. . . . . . . . . . . . . . . . . . . . . . .

T able 22: Second Equipment Settings for LF Adjustments 45. . . . . . . . . . . . . . . .

T able 23: Electrical Faults 54. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ADA400A Differential Preamplifier

ii

General Safety Summary

Review the following safety precautions to avoid injury and prevent damage to
this product or any products connected to it.

Only qualified personnel should perform service procedures.

Injury Precautions

Avoid Electric Overload

Ground the Product

Do Not Operate Without

Covers

Do Not Operate in

To avoid electric shock or fire hazard, do not apply a voltage to a terminal that is
outside the range specified for that terminal.

This product is grounded through the grounding conductor of the oscilloscope
power cord. To avoid electric shock, the grounding conductor must be connected
to earth ground. Before making connections to the input or output terminals of
the product, ensure that the product is properly grounded.

To avoid electric shock or fire hazard, do not operate this product with covers or
panels removed.

To avoid electric shock, do not operate this product in wet or damp conditions.

Wet/Damp Conditions

Do Not Operate in

Explosive Atmosphere

To avoid injury or fire hazard, do not operate this product in an explosive
atmosphere.

Product Damage Precautions

Do Not Operate With

Suspected Failures

Do Not Immerse in Liquids

ADA400A Differential Preamplifier

If you suspect there is damage to this product, have it inspected by qualified
service personnel.

Clean the instrument using only a damp cloth. Refer to cleaning instructions.

iii

General Safety Summary

Safety Terms and Symbols

Terms in This Manual

Terms on the Product

These terms may appear in this manual:

WARNING. Warning statements identify conditions or practices that could result
in injury or loss of life.

CAUTION. Caution statements identify conditions or practices that could result in
damage to this product or other property.

These terms may appear on the product:
DANGER indicates an injury hazard immediately accessible as you read the

marking.
WARNING indicates an injury hazard not immediately accessible as you read the

marking.
CAUTION indicates a hazard to property including the product.

Symbols on the Product

iv

The following symbols may appear on the product:

DANGER

High Voltage

Protective Ground

(Earth) T erminal

ATTENTION

Refer to

Manual

ADA400A Differential Preamplifier

Double

Insulated

Preface

This manual contains both user and service information for the ADA400A
Differential Preamplifier. The following is a brief overview of what each section
of the manual contains.

H Getting Started includes a description of the product features and a list of

standard and optional accessories. This section also describes how to supply
power to the preamplifier and how to connect the preamplifier to an
oscilloscope.

H Operating Basics contains a graphical overview and a brief description of

each control and connector of the ADA400A Differential Preamplifier.

H The Reference section describes how to connect the ADA400A Differential

Preamplifier to small signals and make the proper settings.

H Specifications lists the electrical and mechanical characteristics of the

ADA400A Differential Preamplifier.

H Performance Verification contains procedures for verifying the warranted

characteristics of the ADA400A Differential Preamplifier.

H The sections behind the warning page contain service information for the

ADA400A Differential Preamplifier: Adjustment Procedures, Maintenance
and Replaceable Parts.

ADA400A Differential Preamplifier

v

Preface

Contacting Tektronix

Phone [phone]*

Address Tektronix, Inc.

Department or name (if known)
14200 SW Karl Braun Drive
P.O. Box 500
Beaverton, OR 97077
USA

Web site www.tektronix.com

Sales support 1-800-833-9200, select option 1*

Service support 1-800-833-9200, select option 2*

Technical support Email: [e-mail]

1-800-833-9200, select option 3*
1-503-627-2400

6:00 a.m. – 5:00 p.m. Pacific time

* This phone number is toll free in North America. After office hours, please leave a

voice mail message.
Outside North America, contact a Tektronix sales office or distributor; see the
Tektronix web site for a list of offices.

ADA400A Differential Preamplifier

vi

Getting Started

Product Description

Getting Started includes a description of the product features and a list of
standard and optional accessories. This section also describes how to supply
power to the preamplifier and how to connect the preamplifier to an oscilloscope.

The ADA400A Differential Preamplifier allows direct oscilloscope measure­ments of very low amplitude voltages and signals that do not have a ground
reference. These measurements are typical in setups that depend on transducers
or other sensitive devices to supply the electrical signal.

Highlights of the ADA400A Differential Preamplifier are as follows:
H Selectable gains of X100, X10, X1, and X0.1 provide wide range of

sensitivity.

H Common-mode rejection of greater than or equal to 100,000 to 1 in the

frequency range of DC to 10 kHz removes unwanted common mode
electrical noise from sensitive pickups.

Accessories

H Bandwidth of greater than or equal to 1 MHz amplifies signals with fast

transients. Selectable bandwidth limits of 100 Hz, 3 kHz, 100 kHz reject
normal-mode noise.

H Input impedance of 1 MW in all settings and selectable impedance of

infinite W (u10
impedance prevents loading down signals with high source impedance.

H Adjustable differential offset allows the user to null out transducer bridge

bias, galvanic potentials from the test setup, or other DC voltages.

H Special circuitry greatly reduces the annoying DC drift commonly found in

older types of differential preamplifiers.

H TEKPROBE Interface provides power input and signal output connections.

Standard accessories for the ADA400A Differential Preamplifier include the
following items:

H This instruction manual
H Two spare input fuses

12

W) in X100 and X10 gain settings. The high input

ADA400A Differential Preamplifier

1

Getting Started

Installation

Recommended accessories for the ADA400A Differential Preamplifier include
the following items:

H P6101B 1X Passive Probe
H 1103 Probe Power Supply for oscilloscopes that do not have the TEK-

PROBE Interface.

Before you connect the output of the ADA400A Differential Preamplifier,
determine whether or not your oscilloscope has the TEKPROBE interface. The
interface provides connections for power, signal, and scale factor coding for
compatible probes and accessories.

Oscilloscopes with the

TEKPROBE Interface

The polarized output connector of ADA400A Differential Preamplifier connects
to any oscilloscope with the TEKPROBE interface.

NOTE. To avoid misleading scale factor readouts of the ADA400A Differential
Preamplifier, the oscilloscope must be compatible with the scale factor coding;
otherwise, you must remove the preamplifier housing and disconnect the internal
line that carries the scale factor coding.

Compatible Oscilloscopes. Most oscilloscopes with the TEKPROBE interface,
except the 11000 Series models, are compatible with the scale factor coding of
the ADA400A Differential Preamplifier. The factory configures the internal
jumper to connect the scale factor coding. See Figure 1.

Perform the Functional Check on page 4, steps 1–6, and verify that the
oscilloscope volt/division readings match the manual for all gain settings in step

6. If the readings are not correct for any scale setting, the oscilloscope is not
compatible with the scale factor coding of the ADA400A Differential Preamplifi­er. In this case, use the procedure that follows to disable the scale factor coding.

1. Remove the top housing of the preamplifier by following the procedures on

page 50.

2. Identify the jumper on the data line (See Figure 1) and position the jumper to

disable the scale factor coding.

3. Replace the top housing on the preamplifier box.

ADA400A Differential Preamplifier

2

Figure 1: Configuration Jumper for Scale Factor Coding

Getting Started

Enabled Disabled

Oscilloscopes without the

TEKPROBE Interface

Because the line that carries the scale factor coding is disabled, see the chart on
page 10 to correctly interpret the volts/division setting of the oscilloscope.

Connecting the TEKPROBE Output. To engage the TEKPROBE output, align the
fin on the output head counterclockwise with the clearance on the oscilloscope
connector. Push the connector in and and lock the fin clockwise.

Use the 1103 TEKPROBE Power Supply to connect the ADA400A Differential
Preamplifier to any oscilloscope that does not provide TEKPROBE power. The
1103 TEKPROBE Power Supply has connections for two probe channels.

NOTE. Use the offset controls of the ADA400A Differential Preamplifier to adjust
the offset level. The offset controls on the 1103 TEKPROBE Power Supply do not
operate with the ADA400A Differential Preamplifier.

Because the 1103 TEKPROBE Power Supply does not connect the line that
carries the scale factor coding, see the chart on page 10 to correctly interpret the
volts/division setting of the oscilloscope.

For more information about using the 1103 TEKPROBE Power Supply, refer to
the instruction manual that comes with the power supply.

ADA400A Differential Preamplifier

3

Getting Started

Check the Oscilloscope

Input Impedance and

Coupling

Functional Check

Always set the input impedance of the oscilloscope to 1 MW and the input
coupling of the oscilloscope to DC. Setting the impedance to 50 W loads
(reduces) the amplitude of the output signal from the ADA400A Differential
Preamplifier. AC coupling on the oscilloscope interferes with the signal output.
Use the input coupling switch on the preamplifier to select other types of signal
coupling.

The following procedure checks the output level of the ADA400A Differential
Preamplifier and the functionality of the offset controls with no signal applied.

1. Without any connection on the input of the oscilloscope, power on the

oscilloscope and make the following control settings:
Volts/Division 100 mV

Time/Division 100 ms
Input Coupling DC
Input Impedance 1 MW

2. Adjust the oscilloscope to display a flat signal trace at center screen.

3. Connect the output of the ADA400A Differential Preamplifier (or 1103

TEKPROBE Power Supply) to the input connector of the oscilloscope.

4. With no input signal or voltage connected, make the following control

settings on the ADA400A Differential Preamplifier:
AC GND DC GND (both inputs)

GAIN 0.1
OFFSET OFF
UPPER BANDWIDTH FULL (1 MHz)

5. Check that the trace on the oscilloscope centers around zero volts and the

OVERRANGE indicator does not light.

6. Set the GAIN switch to each of the higher gain settings and check that the

trace on the oscilloscope is adjustable to center screen. Make sure the
volts/division reading on the scope matches the readings below in table 1. If
the readings do not match, the oscilloscope is not compatible with the scale
factor coding of the ADA400A Differential Preamplifier. See page 2. If the
scale factor coding is disabled, see table 3 on page 10 for proper readings.

ADA400A Differential Preamplifier

4

Getting Started

T able 1: Gain settings

Gain setting Oscilloscope reading

0.1 1.00 V
1 100 mV
10 10.0 mV
100 1.00 mV

7. With the GAIN switch on the highest setting, set the ON OFF switch for the
OFFSET controls to ON.

8. Adjust the COARSE and FINE controls to bring the trace to center screen.

9. Set each input separately to AC, DC, and back to GND and check that the

offset controls still bring the trace to center screen for each setting.

10. Return the GAIN setting to .1 and the input coupling switches to GND.

The ADA400A Differential Preamplifier is now ready to use. For a complete
performance verification procedure, refer to page 29.

ADA400A Differential Preamplifier

5

Getting Started

ADA400A Differential Preamplifier

6

Operating Basics

Vertical Gain Control

Operating Basics contains a graphical overview and a brief description of each
control and connector of the ADA400A Differential Preamplifier. See Figures 2
through 4 and Table 2.

W

W1

Input Coupling

Overrange Indicator

Upper Bandwidth

Selector

}
}

Vertical Offset
Controls

Figure 2: Front Panel Controls

ADA400A Differential Preamplifier

7

Operating Basics

+ Input Fuse – Input Fuse– Input BNC

+ Input BNC

Connector

Figure 3: Input Connectors and Fuses

Connector

Signal Output

BNC

TEKPROBE Interface Pins

Figure 4: Output Connector

ADA400A Differential Preamplifier

8

T able 2: Controls, Connectors, and Indicators

Feature Description

Input BNCs. The BNC connectors provide the differential input connections to the

preamplifier. These connectors accept coaxial cables, 1X probes, adapters, or other input
leads that terminate with male BNC connectors. Before connecting the inputs, see
page 11.

NOTE. Avoid using attenuating probes. The slightest difference in attenuation match

+ Input BNC

Connector

– Input BNC

Connector

greatly lowers the common-mode rejection ratio.

Input Fuses. The input fuses and internal circuitry protect the input circuits from
excessive surge currents. To replace the fuses, see page 50.

Operating Basics

+ Input

Fuse

}
}

– Input

Fuse

W

W1

Selectable Impedance. Internal jumpers select infinite impedance for measuring signals
with high source impedance. To select the input impedance, see page 12.

Input Coupling Switches. Use the input coupling switches to select the proper mode for
coupling the input signals to the internal inputs of the preamplifier.

The AC position couples the input signal through a capacitor and blocks any DC and AC
components of the signal from 0 to 2 Hz.

GND decouples the signal from the input and couples the internal input of the
preamplifier to ground. This position also precharges the coupling capacitor to the DC
level of the input signal (see page 16).

The DC position couples both AC and DC components of the input signal.
Overrange Indicator. The OVERRANGE indicator lights red when the signal input

exceeds the selected range of the amplifier. If the indicator is on, the output signal is not
a true representation of the input signal(s). See page 16.

Gain Selector. The gain selectors set the gain of the preamplifier to X0.1, X1, X10, or
X100. If the oscilloscope does not display the correct volts per division for each gain
setting, refer to Table 3 on page 10.

Offset Controls. The ON/OFF switch activates the offset controls. The COARSE and
FINE controls provide a maximum of 40 volts offset in the X0.1 and X1 gain settings and
a maximum of 1 volt offset in X10 and X100 gain settings. See page 16.

ADA400A Differential Preamplifier

9

Operating Basics

T able 2: Controls, Connectors, and Indicators (Cont.)

Feature Description

Upper Bandwidth Selector. The Upper Bandwidth Selector reduces electrical

interference by limiting the frequency response of the amplifier to FULL (1 MHz),
100 kHz, 3 kHz, or 100 Hz.

Output Connector. The output connector contains connections for the TEKPROBE
interface and signal output.

Determining the Effective Volts/Division

If your oscilloscope cannot read the scale factor information, see Table 3 to
determine the effective volts/division setting. The effective volts per division is
the volts per division setting of the oscilloscope divided by the gain setting of
the ADA400A Differential Preamplifier. For example, if the volts/division
setting on the oscilloscope is 500 mV/division and the gain setting is 10, the
effective volts/division is 500 divided by 10 or 50 mV.

T able 3: Effective Volts Per Division Settings

Scope Volts/Div

1 10 1 100 m 10 m
500 m 5 500 m 50 m 5 m
200 m 2 200 m 20 m 2 m
100 m 1 100 m 10 m 1 m
50 m 500 m 50 m 5 m 500 m
20 m 200 m 20 m 2 m 200 m
10 m 100 m 10 m 1 m 100 m

Gain = .1

Effective Volts Per Division

Gain = 1 Gain = 10 Gain = 100

10

5 m 50 m 5 m 500 m 50 m
2 m 20 m 2 m 200 m 20 m
1 m 10 m 1 m 100 m 10 m

ADA400A Differential Preamplifier

Reference

Connecting the Inputs

The Reference section describes how to connect the inputs of the ADA400A
Differential Preamplifier and make the proper control settings. To achieve the
best performance it is important to make the proper signal and ground connec­tions, set the controls to optimize the performance of the preamplifier, and
reduce unwanted electrical interference.

Making the proper input connections is crucial to maintaining the fidelity of the
signal as well as eliminating unwanted noise. The characteristics of the signal
source and the type of measurement you wish to make, determine the type of
input leads you should use and the way you should connect the inputs.

WARNING. Do not attach the ADA400A Differential Preamplifier to human
subjects for any testing or bio-monitoring. The ADA400A Differential Preampli­fier is not safety certified for direct connection to humans.

Input Devices

The ADA400A Differential Preamplifier is able to amplify extremely small
signals that may or may not have a ground reference. Often the signals originate
from low-level, low-frequency transducers, and other similar sources of small
differential or floating voltages.

The inputs of the ADA400A Differential Preamplifier connect easily to devices
or leads that terminate with male BNC connectors. There are numerous adapters
readily available that can adapt other types of wire, cables, or plugs to a BNC
connector.

NOTE. Avoid using attenuating probes. The slightest difference in attenuation
match greatly lowers the common-mode rejection ratio.

ADA400A Differential Preamplifier

11

Reference

Using the Proper Input

Leads

Input Voltages

Input Protection

To reduce unwanted electrical interference on the input leads, use shielded
coaxial cable or the recommended 1X probes to connect signals to the preampli­fier inputs. The shielding in these types of leads intercepts and shunts electrical
noise to ground.

When you must use any length of unshielded wire, twist the wires together and
connect the wires differentially. Twisting the wires together helps to introduce
any electrical interference as common-mode noise that the differential preampli­fier cancels out with a differential setup on the inputs.

For other tips on reducing signal interference, refer to page 19.

Because the ADA400A Differential Preamplifier is designed to amplify small
DC and AC voltages, do not connect voltages that exceed the input rating.

CAUTION. To avoid damaging the inputs of the ADA400A Differential Preampli­fier, do not apply more than 40 volts (DC + peak AC) between any one input and
ground or 80 volts (DC + peak AC) differential between the inputs.

To prevent damage to the input circuitry from the misapplication of large
voltages, a fuse on each input opens if the input current exceeds 62 mA (
To replace or check these fuses, refer to the procedure on page 50.

1

/16 A).

12

Input Impedance

Each input connector of the ADA400A Differential Preamplifier has a character­istic input impedance of 1 MW to ground in parallel with approximately 55 pF.
For low source impedances, this 1 MW is more than adequate to prevent the
inputs from loading the signal source.

If impedance of the signal source approaches 1 MW, the impedance of the inputs
begin to load the signal source and reduce the amplitude. In effect, the extremely
low current of the signal source is not able to develop a voltage across the 1 MW
resistance and there is no signal to amplify. In this case you may want to select
the infinite W position.

Infinite W. To measure signals from high impedance sources, you can internally
disconnect the 1 MW resistance of the ADA400A Differential Preamplifier. and
select the infinite W position. This position prevents the preamplifier from
loading a high impedance signal source.

Observe the following operating limitations when you select the infinite W
position:

H Select either the X100 or the X10 gain position. Operation in the 0.1X and

1X gain results in gain errors.

ADA400A Differential Preamplifier

Reference

H Ensure that the source has some impedance to ground. The internal input

amplifier requires some input bias current to operate. Typically this amount
of input bias current is less than 25 pA.

H Select the DC coupling position when operating the preamplifier. The AC

coupling position blocks the bias current that the preamplifier input requires
to operate.

H Take steps to reduce interference from other sources (see page 19). Because

the input impedance is essentially infinite you may notice an increased
susceptibility to noise and DC drift.

Selecting the Infinite W Position. To select the infinite impedance, remove the
knobs and top housing of the preamplifier. Do not remove the inner shield. With
a pair of needle-nose pliers or tweezers, move the jumpers from the 1 MW to the
infinite W position as Figure 5 illustrates.

Input Configurations

–

Input+ Input

Infinite W

1 MW

Figure 5: Selecting the Input Impedance

There are two basic types of input configurations on the ADA400A Differential
Preamplifier: single-ended or differential. Whether one or the other of these
configurations is appropriate depends on the type of signal and the electrical
environment of the test setup.

Single-Ended. To monitor a ground-referenced signal you only need to make a
single input connection. All the controls on the preamplifier still operate. The
only difference is that the preamplifier cannot cancel out common mode noise
without using the other input connection. When making single-ended measure­ments, set the coupling for the unused input to GND.

ADA400A Differential Preamplifier

13

Reference

Single-ended measurements, however, often yield unsatisfactory information
because of interference resulting from ground-loop currents between the
oscilloscope and the device under test. In other cases, it is desirable to eliminate
a common-mode DC voltage without using a DC blocking capacitor or the AC
coupling capacitor of the preamplifier. These capacitors limit low-frequency
response. Connecting the signals differentially virtually eliminates these effects.

Differential. Figure 6 shows two signals connected to the ADA400A Differential
Preamplifier. One signal is connected to the + input and the other is connected to
the – input. Because the preamplifier inverts the signal at the – input, the
preamplifier amplifies only differential voltages between the inputs and rejects
(cancels) voltages that are common to both inputs. The oscilloscope displays the
waveform of the differential signal only.

NOTE. To avoid creating a fictitious differential offset, set both AC GND DC
coupling switches to the same AC or DC switch position.

+

Differential

Amplifier

–

Figure 6: Differential Rejection of Common-Mode Signal

To avoid ground loops in a differential setup it is important to leave the grounds
of the shielded coax disconnected and to route the chassis ground to the
oscilloscope ground using a separate ground lead. Figure 7 on page 15 illustrates
this type of connection.

14

ADA400A Differential Preamplifier

Reference

Oscilloscope Input

Impedance and Coupling

Setting the Controls

+

Differential

Amplifier

–

Circuit

Under Test

Common Ground

Oscilloscope

Input

Figure 7: Eliminating Ground Loops in a Differential Setup

Always set the input impedance of the oscilloscope to 1 MW and the input
coupling of the oscilloscope to DC. Setting the impedance to 50 W loads
(reduces) the amplitude of the output signal from the ADA400A Differential
Preamplifier. AC coupling on the oscilloscope interferes with the signal output.
Use the input coupling switch on the preamplifier to select other types of signal
coupling.

Input Coupling

The controls of the ADA400A Differential Preamplifier determine signal
coupling, amplification, DC offset, and the bandwidth limit.

The type of input coupling you select depends on whether or not you want to
pass or block the DC component of the input signal.

AC Coupling. Setting the coupling switch to AC places a capacitor in the signal
path and blocks DC to about 2 Hz signals. Select the AC position to block DC
components on the signal input and couple AC signals higher than approximate­ly 2 Hz. This setup is useful when the test setup has a DC bias which drifts.

NOTE. To prevent the circuit under test from receiving the effects of charging and
discharging the AC coupling capacitor, refer to the procedure for Precharging

the Signal Input in the section that follows.

ADA400A Differential Preamplifier

15

Reference

GND Coupling. The GND position decouples the signal from the input and
couples the internal input of the preamplifier to ground. This position also
precharges the AC coupling capacitor to the DC level of the signal. (See the
following section, Precharging the Signal Input.)

DC Coupling. The DC position couples all signal components, AC and DC, to the
preamplifier. (You can adjust the offset controls to null out DC biases.)

Precharging the Signal

Input

Gain, Input Range, and

Offset Range

Follow the procedure below when coupling AC signals that have a high DC
voltage level or when probing between signals that differ greatly in DC levels.
This procedure becomes especially useful when you disable the 1 MW input
resistance and it takes a long time to charge the input capacitors back to the bias
voltage.

1. Set the input coupling switch to GND before connecting the input to a signal

source.

2. Connect the preamplifier input to the signal source.

3. Wait two seconds for the input coupling capacitor to charge to the DC level

of the signal source.

4. Set the input coupling switch to AC. Position the AC signal within the

graticule area on the oscilloscope display.

The gain selector sets amplification factor of the preamplifier to X0.1, X1, X10,
or X100. Each gain setting has a characteristic differential or single-ended range,
a common-mode (dynamic) range, and variable offset range. To prevent the
signal from distorting or “clipping” (see Figure 10) you must use the appropriate
gain setting and offset.

The amount of differential, common-mode, and offset range depends on the gain
setting. Figures 8 through 11 beginning on page 17 show the common-mode,
differential, and offset range for each gain setting of the preamplifier.

16

The OVERRANGE indicator lights when the input signal is outside the
differential input range for a particular gain setting. This light indicates that the
output signal is distorted or “clipped” and the oscilloscope display may not be
accurate. Try a lower gain setting or check the position of the offset controls if
the OVERRANGE indicator is on.

ADA400A Differential Preamplifier

80
40

30
20
10

–10
–20
–30
–40

–80

Maximum

Single-Ended

Input

Common-Mode

and Offset

Range

Figure 8: Input and Offset Range for X 0.1 Gain

40
30
20
10

–10
–20
–30
–40

Maximum
Differential or
Single Ended Input

Common-Mode

Range and Offset

Range

Reference

Maximum

Differential Input

Figure 9: Input and Offset Range for X 1 Gain

(“Clipped”

+10 V

Maximum

Differential and

Single-Ended Input

+1 V

–1 V

–10 V

Waveform)

Common-Mode

Range

Offset Range

Figure 10: Input and Offset Range for X 10 Gain

ADA400A Differential Preamplifier

17

Reference

+10V

Adjusting the Offset

Controls

+1V

+100mV

–100mV

–1V

–10V

Maximum

Differential and

Single-Ended Input

Offset Range

Common Mode

Range

Figure 11: Input and Offset Range for X 100 Gain

Setups that have a large DC offset, but must measure small changes in DC
voltage or signal voltage below 2 Hz, require that you to adjust the offset
controls of the preamplifier. Typical setups include those with transducers or
setups that measure galvanic potentials.

To compensate for a DC offset, perform the following procedure:

1. Set the input coupling to GND on both inputs of the preamplifier and switch
offset controls to OFF.

18

Limiting Bandwidth

2. Preset the GAIN switch of the preamplifier and the volts/division switch of
the oscilloscope to the appropriate settings based on the amount of offset you
expect to measure. See Figures 8 through 11. (Select a lower gain setting if
you are unsure of the amount of the offset.)

3. Center the oscilloscope display using the vertical position control on the
oscilloscope.

4. Set the offset controls ON and center the display with the COARSE and
FINE offset controls.

5. Set the input coupling to DC on the signal input(s) and, if necessary,

measure the amount of DC offset.

6. Center the display using the COARSE and FINE controls and change the
volts/division setting on the oscilloscope to better display the signal.

The ADA400A Differential Preamplifier has a selector for limiting the upper
bandwidth. Limiting the bandwidth is desirable in setups where electrical
interference from higher frequency sources is a problem. The ADA400A

ADA400A Differential Preamplifier

Differential Preamplifier allows you to select upper bandwidth limits of FULL
(1 MHz), 100 kHz, 3 kHz and 100 Hz.

Tips for Reducing Signal Interference

Disruptive electrical interference or “noise” from sources near the test setup can
affect measurements. The effects become even more apparent when measuring
low-amplitude voltages.

The electric-power system, for example, generates a line frequency of 50 or
60 Hz and can couple electrical noise from other devices. Power switches or
switching devices generate power line spikes. Unshielded or poorly grounded
electric motors can generate disruptive transients. Power lines and transformers
create magnetic fields that can induce a disruptive voltage in wires or input leads
that are not properly twisted together.

Devices such as digital or microprocessor based systems can radiate signals that
sensitive electronic detectors or amplifiers can receive and amplify. Switch-mode
power supplies generate interference in the range of 20 to 100 kHz. Sources of
interference can include florescent lights, laser printers, monitors, CRTs, even
radio transmissions.

Reference

Signal and Ground

Connections

Proper setup of the ADA400A Differential Preamplifier minimizes or eliminates
signal interference in most cases. There are three important strategies to reducing
signal interference:

1. Use the proper signal and ground connections for the particular application.

2. Limit the bandwidth of the test setup.

3. Isolate or eliminate sources of signal interference.

The techniques for proper signal and ground connections involve limiting noise
to the input:

H Minimize length of input leads.
H Select input leads that have the same length and type of construction.
H Use shielded coaxial cable or “twisted-pair” leads on the inputs.
H Connect shield or ground leads close to signal source.
H Restrict movement of input leads.
H Eliminate ground loops.
H Reject common-mode noise by operating in differential mode.

ADA400A Differential Preamplifier

19

Reference

Bandwidth Limiting

Isolating or Eliminating

Sources of Interference

Limiting the bandwidth is a useful technique for keeping unwanted high
frequency noise from interfering with the display of lower frequency signals. The
ADA400A Differential Preamplifier allows you to limit the upper bandwidth to
100 Hz, 3 kHz, 100 MHz, and FULL (1 MHz).

Some pieces of electronic or electrical equipment can generate enormous
amounts of electrical noise. One solution is to isolate or eliminate the noise that
these devices emit:

H Move sources of noise away from test setup or isolate test setup.
H Shield test setup.
H Make sure all electronic equipment that is connected to the AC power line is

properly grounded through the power cord.

20

ADA400A Differential Preamplifier

Specifications

This section describes three classes of characteristics for the ADA400A
Differential Preamplifier: nominal, warranted, and typical.

Nominal Characteristics

Nominal traits are described using simple statements of fact such as “Differen-
tial, ‘+’ and ‘–’” for the characteristic “Input Configuration,” rather than in terms
of limits that are performance requirements.

T able 4: Nominal Characteristics — Signal Acquisition System

Name Description

Input Configuration Differential, ‘+’ and ‘–’
Input Coupling DC, AC, or GND

Ground coupling connects a ground reference to the input of the attenuator or
differential amplifier and allows the AC coupling capacitor to charge up to the

input voltage through a large resistance.
Gain Settings 0.1, 1, 10, 100
Analog Bandwidth Selections 100 Hz, 3 kHz, 100 kHz, and FULL (1 MHz)
Offset Ranges Gain Setting Offset Range

0.1 ± 40 V

1 ± 40 V

10 ± 1 V

100 ± 1 V

ADA400A Differential Preamplifier

21

Specifications

Warranted Characteristics

Warranted characteristics are described in terms of quantifiable performance
limits which are warranted.

NOTE. In these tables, those warranted characteristics that are checked in the
procedure Performance Verification appear in boldface type under the column

Name.

The performance limits in this specification are valid with these conditions:

H This instrument must have been calibrated/adjusted at an ambient tempera-

H The instrument must be in an environment with temperature, altitude,

H The instrument must have had a warm-up period of at least 20 minutes.

ture of 22 ± 5_ C.

humidity, and vibration within the operating limits described in these
specifications.

H The instrument must be used with an oscilloscope that is compatible with the

scale factor coding of the ADA400A Differential Preamplifier. See page 2.

T able 5: Warranted Characteristics — Signal Acquisition System

Name Description
Input Resistance, DC Coupled 1 MW ±2%
DC Gain Accuracy ±2%

Maximum Input Voltage 30 VAC

input; derate at 20 dB/decade above 1 MHz.

Differential Signal Range (DC OFFSET not used) Gain Setting Differential Input Signal Range

0.1 ±80 V
1 ±10 V
10 ±1 V
100 ±100 mV

Common Mode Signal Range Gain Setting Common Mode Input Signal Range

0.1 ±40 V
1 ±40 V
10 ±10 V
100 ±10 V

, 42 V (DC + peak AC), between signal and common of the same

RMS

22

ADA400A Differential Preamplifier

T able 5: Warranted Characteristics — Signal Acquisition System (Cont.)

Name Description

Specifications

Common Mode Rejection Ratio

(See Figures 14 to 15 on page 27.)

1

The limits given are for the ambient temperature of 22 ±5_ C

Frequency Gain Setting

100 Hz 10 85 dB

10 kHz 85 dB

100 kHz 60 dB

100 Hz 100 90 dB

10 kHz 90 dB

100 kHz 60 dB

T able 6: Warranted Characteristics — Environmental

Name Description

Atmospherics Temperature

Operating: 0_ C to +50_ C
Non-operating: –55_ C to +75_ C

Relative Humidity (tested to the following limits)

Operating: 90–95% RH, +30_ C to +50_ C

CMRR1
(DC coupled)

Non-operating: 90–95% RH, +30_ C to +60_ C

Dynamics Random Vibration

Operating: 2.66 g rms overall, 3 axis, 20 min/axis (60 min total)
Non-operating: 3.48 g rms overall, 3 axis, 20 min/axis (60 min total)

Mechanical Shock

Half Sine, 500 g’s
3 axis, 3 drops each axis, 1 ms duration, 18 drops total

ADA400A Differential Preamplifier

23

Specifications

T able 6: Warranted Characteristics — Environmental (Cont.)

Name Description

Electromagnetic Compatibility (EMC) Emissions:

Meets or exceeds the requirements of the following standards:

EN 55022 Class B limits for radiated emissions when operated as a
system with a TDS460 series oscilloscope (FCC 47 CFR, Part 15,
Subpart B for Class A equipment.)

ADA400A Settings: Gain=100; Offset=off; DC coupled; Filter=1 MHz
TDS 460 Settings: 500 ns/div; 5 mV/div; DC coupled

Immunity:
Radio Frequency Electromagnetic Field

less than ±2 divisions of leakage signal when the instrument is subjected
to a 3 V/M electromagnetic field over the frequency range of 27 MHz to
500 MHz.

Electrostatic Discharge (ESD)

Up to 8 kV with no change to control settings of impairment of normal
operation, and up to 15 kV with no loss of stored data or damage that
prevents recovery of normal operation by the user.

Typical Characteristics

Typical characteristics are described in terms of typical or average performance.
Typical characteristics are not warranted.

T able 7: Typical Characteristics — Signal Acquisition System

Name Description

Input Capacitance 55 pF ± 20%
Analog Bandwidth Selection Accuracy ± 12% for 100 Hz, 3 kHz, 100 kHz selections

≥ 1 MHz for the FULL (1 MHz) selection
Linearity ± 0.01% of linear dynamic range
Lower Frequency Limit, AC Coupled ≤ 2 Hz (lower –3 dB frequency)
Harmonic Distortion ≤ 0.002% measured using 3 V
Recovery Time ≤ 1.5 ms to recover to within 0.5% of zero level after over driving the amplifier

by ± 150%

output at 100 Hz and 1 kHz

RMS

24

ADA400A Differential Preamplifier

T able 7: Typical Characteristics — Signal Acquisition System (Cont.)

Name Description

Specifications

Zero Offset
(Offset control off)

DC Offset Drift with Temperature Gain Setting Offset On Offset Off

Input Current Less than 25 pA at an ambient temperature of 22 ± 5_ C
Random Noise RMS Noise

Bandwidth Selection Gain of 0.1 Gain of 1 Gain of 10 Gain of 100

1 MHz ≤5 mV ≤3 mV ≤50 mV ≤30 mV
100 kHz ≤4 mV ≤1 mV ≤40 mV ≤10 mV
3 kHz ≤4 mV ≤1 mV ≤40 mV ≤10 mV
100 Hz ≤4 mV ≤1 mV ≤40 mV ≤10 mV

Common Mode Rejection Ratio
(See Figures 12 to 15 on pages 26 to 28)

Gain Setting

0.1 ±50 mV
1 ±5 mV
10 ±500 mV
100 ±50 mV

0.1 0.750 mV/_ C 0.250 mV/_ C
1 0.300 mV/_ C 0.200 mV/_ C
10 10 mV/_ C 5 mV/_ C
100 5 mV/_ C 3 mV/_ C

Frequency Gain Setting

100 Hz 0.1 60 dB 45 dB
10 kHz 52 dB 50 dB
100 kHz 50 dB 50 dB
100 Hz 1 75 dB 50 dB
10 kHz 60 dB 55 dB
100 kHz 52 dB 52 dB
100 Hz 10 100 dB 75 dB
10 kHz 100 dB 95 dB
100 kHz 90 dB 90 dB
100 Hz 100 100 dB 80 dB
10 kHz 100 dB 100 dB
100 kHz 90 dB 90 dB

Zero Offset Referred to the Input of
the Amplifier

CMRR
(DC coupled)

CMRR
(AC coupled)

ADA400A Differential Preamplifier

25

Specifications

T able 8: Typical Characteristics — Mechanical Characteristics

Name Description

Weight Shipping: 1.78 kg (3.92 lbs) including accessories

Net Weight: 1.14 kg (2.51 lbs)
Overall Dimensions Height: 36 mm (1.42 in)

Width: 1 12 mm (4.41 in)

Depth: 203 mm (8.00 in)
Cable Length 2 m (78.7 in)

Gain – 0.1

110
100

90
80
70

dB

DC Typical

60
50

AC Typical

40
30
20
10

0

10 100 1 k 10 k

Frequency (Hz)

Figure 12: Typical DC and AC Coupled CMRR in X0.1 Gain

100 k 1 M

26

ADA400A Differential Preamplifier

Gain – 1.0

110
100

90
80

DC Typical

70

dB

60

AC Typical

50
40
30
20
10

0

10 100 1 k 10 k

Frequency (Hz)

Specifications

100 k 1 M

Figure 13: Typical AC and DC Coupled CMRR in X1 Gain

Gain – 10.0

110

DC Typical

100

90

DC Warranted

80

AC Typical

70

dB

60
50
40
30
20
10

0

10 100 1 k 10 k

Frequency (Hz)

100 k 1 M

Figure 14: Typical and Warranted CMRR in X10 Gain

ADA400A Differential Preamplifier

27

Specifications

Gain – 100.0

110

DC Typical

100

DC Warranted

90
80

AC Typical

70

dB

60
50
40
30
20
10

0

10 100 1 k 10 k

100 k 1 M

Frequency (Hz)

Figure 15: Typical and Warranted CMRR in X100 Gain

28

ADA400A Differential Preamplifier

Performance Verification

This section contains procedures for checking that the ADA400A Differential
Preamplifier meets warranted specifications.

Requirements for Performance

The performance limits of this procedure are valid with the following conditions:
H The ADA400A Differential Preamplifier is in an environment that is within

the operating limits of temperature, altitude, humidity, and vibration
described in Specifications.

H The data line jumper located inside the ADA400A Differential Preamplifier.

is properly configured depending on the type of oscilloscope you connect to
the output. See the Installation section on page 2.

H The ADA400A Differential Preamplifier has a period of at least a 20 minutes

to warm up prior to verification.

Equipment Required

Table 9 lists the equipment required to verify and adjust the ADA400A
Differential Preamplifier. The Adjustment Procedures section begins on page 37.

T able 9: Test Equipment

Item Number and
Description

1. Digitizing Oscilloscope Bandwidth: > 5 MHz

2. Sine Wave Generator Frequency Range: 1 Hz to

3. Digital Multimeter Resolution: ≥ 3.5 digits

Minimum Requirements Example Purpose

Sensitivity: 1 mV/div
Auto Measurement: Frequency,
Amplitude
Input Impedance: 1 MW
Must have TekProbe Level 2
Meet functional check with
scale factor coding (see page

2).

5 MHz

Accuracy: ≤ 0.5%
Resistance Range: 200 W to
10 MW

–– Supply power to and display

output of ADA400A

SG5030 CMRR checks and adjustments

DM2510 Input resistance check

ADA400A Differential Preamplifier

29

Performance Verification

T able 9: Test Equipment (Cont.)

Item Number and
Description

PurposeExampleMinimum Requirements

4. Calibration Generator Calibrated Amplitude:

Period: 1 ms
Amplitude: 50 mVp-p to
20 V p-p into 1 MW
Aberrations: ≤ 2% p-p
Accuracy: ≤ 0.5%

Fastrise: ≤ 500 ns
1 Vp-p into 50 W

5. BNC Adapters BNC Female to Dual Banana Tektronix part number

6. Dual Input Connector Dual Input Cable BNC Tektronix part number

7. 50 W Terminators (2) 50 W, 2W, BNC Tektronix part number

8. 10X Attenuators (2) 10:1 Attenuator, 50 W, BNC Tektronix part number

9. Coaxial Cables (2) 50 W, 36 in. L, BNC male both

ends

10. Adjustment Tool, Probe Plastic Insulated Tektronix part number

CG5011 Gain check and adjustment.

103–0090–00

067–0525–02

011–0049–01

011–0059–02
Tektronix part number

012–1341–00

003–0675–01

LF Compensation adjustments

Signal connection

Signal connection

Signal connection

Signal attenuation

Signal connection

Adjustments (Adjustment
Procedure only)

Procedures

30

Before beginning the procedures in this section, connect the output of the
ADA400A Differential Preamplifier to the oscilloscope, turn the oscilloscope on,
and let the ADA400A warm up for 20 minutes.

NOTE. Before performing these procedures, make sure your oscilloscope can
display the proper scale factor. If you are using an oscilloscope that is not
compatible with the scale factor coding of the ADA400A Differential Preamplifi­er to perform these procedures, see page 2 to properly configure the scale factor
coding.

To convert the volts/division settings for oscilloscopes that cannot read the scale
factor from the ADA400A, multiply the volts/div setting in the procedure by the
gain setting of the ADA400A.

ADA400A Differential Preamplifier

Performance Verification

Input Resistance

Equipment
Required

One digitizing oscilloscope (item 1) to supply power to the ADA400A
One digital multimeter (item 3)
One BNC female to dual banana connector (item 5)
One coaxial cable (item 9)

1. Set digital multimeter to measure resistance.

2. Connect banana-to-BNC adapter to digital multimeter.

NOTE. To avoid an erroneous resistance measurement, make sure the 1 MW input
resistance jumpers are installed.

3. Set ADA400A ‘+’ input to DC.

4. Connect coaxial cable from ‘+’ input of ADA400A to the BNC-to-banana

adapter on the multimeter.

5. Check input resistance = 1 MW ± 2% (980 kW to 1.02 MW).

6. Remove coaxial cable from ADA400A ‘+’ input and connect it to the

‘–’ input.

Gain

7. Set the ADA400A ‘–’ input to DC.

8. Check input resistance = 1 MW ± 2% (980 kW to 1.02 MW).

Equipment
Required

One digitizing oscilloscope (item 1)
One dual input coupler (item 6)
One calibration generator (item 4)
One coaxial cable (item 9)

1. Connect the ADA400A to Ch1 of the oscilloscope and make the equipment

settings according to Table 10.

T able 10: Equipment Settings for Gain Checks

ADA400A Control Setting

+ Input DC
– Input Gnd
Gain 100
Upper Bandwidth 100 kHz

ADA400A Differential Preamplifier

31

Performance Verification

T able 10: Equipment Settings for Gain Checks (Cont.)

ADA400A Control Setting

Offset Off

Oscilloscope Control Setting

Channel Selection Ch1
Vertical input impedance 1 MW
Vertical gain 10 mV/div
Time base 200 ms/div
Vertical Coupling DC
Vertical Position 0 V (mid-scale)
Trigger Edge
Trigger position 50%
Trigger source Ch4
Acquisition mode Hi Res
Auto Measurement Amplitude
Bandwidth Full

Calibration Generator Control Setting

Output 50 mV, 1 kHz

2. Connect a dual input connector to inputs of ADA400A.

3. Connect a coaxial cable from calibration generator output to dual input

connector.

4. Adjust vertical position knob on the oscilloscope to center square wave on

screen.

5. Check DC gain accuracy is ± 2% (49 to 51 mV). (Use amplitude measure-

ment function.)

6. Set ADA400A gain setting to 10.

7. Set calibration generator to 0.5 V amplitude.

8. Adjust vertical position knob on oscilloscope to center square wave on

screen.

9. Check DC gain accuracy is ± 2% (490 mV to 510 mV).

10. Set ADA400A gain setting to 1.

32

11. Set calibration generator to 5 V amplitude.

ADA400A Differential Preamplifier

Performance Verification

12. Adjust vertical position knob on oscilloscope to center square wave on

screen.

13. Check DC gain accuracy is ± 2% (4.9 V to 5.1 V).

14. Set ADA400A gain setting to 0.1.

15. Set calibration generator to 20 V amplitude.

16. Adjust vertical position knob on oscilloscope to center square wave on

screen.

17. Check DC gain accuracy is ± 2% (19.6 V to 20.4 V).

18. Disconnect setup from the inputs of the ADA400A.

CMRR

Equipment
Required

One digitizing oscilloscope (item 1)
One sine wave generator (item 2)
One dual input coupler (item 6)
One 50 W terminator (item 7)
Two 10X attenuators (item 8)
Two coaxial cables (item 9)

1. Connect the ADA400A to Ch1 of the oscilloscope and make the equipment

settings according to Table 11.

T able 11: Equipment Settings for X100, 100 kHz CMRR Checks

ADA400A Setting

+ Input DC
– Input Gnd
Gain 100
Upper Bandwidth FULL (1 MHz)
Offset Off

Oscilloscope Setting

Vertical gain 2 mV/div
Time base 5 ms/div
Acquisition mode Average
Number of waveforms to average 20
Trigger source Ch4

ADA400A Differential Preamplifier

33

Performance Verification

T able 11: Equipment Settings for X100, 100 kHz CMRR Checks (Cont.)

Sine Wave Generator Setting

Output 100 kHz, 1 Vp-p into 50 W

2. Connect a coaxial cable from sine wave generator trigger output to Ch4 of

the oscilloscope.

3. Connect dual input connector to inputs of ADA400A.

4. Connect 50 W terminator to dual input connector.

5. Connect two 10X attenuators to 50 W terminator.

6. Connect a coaxial cable from sine wave generator output to 10X attenuators.

7. Adjust trigger level for a steady display.

8. Adjust the amplitude of the sine wave generator for 5 divisions on screen.

9. Remove the two 10X attenuators and connect the cable directly to the 50 W

terminator.

10. Set ADA400A ‘–’ input to DC.

11. Set oscilloscope to 1 mV/div.

12. Measure signal is ≤ 1 division (1 mV, 60 dB).

13. Modify the equipment settings according to Table 12.

T able 12: Equipment Settings for X100, 10 kHz CMRR Checks

ADA400A Setting

Upper Bandwidth 100 kHz

Oscilloscope Setting

Vertical gain 2 mV/div
Time base 50 ms/div

Sine Wave Generator Setting

Output 10 kHz

34

14. Set ‘–’ input to GND.

15. Do steps 5 to 10.

16. Set oscilloscope to 10 mV/div. Measure trace is t 3.2 divisions wide (32 mV,

90 dB).

ADA400A Differential Preamplifier

Performance Verification

17. Modify the equipment settings according to Table 13.

T able 13: Equipment Settings for X100, 100 Hz CMRR Checks

ADA400A Setting

Upper Bandwidth 3 kHz

Oscilloscope Setting

Vertical gain 2 mV/div
Time base 5 ms/div

Sine Wave Generator Setting

Output 100 Hz

18. Set ‘–’ input to GND.

19. Do steps 5 to 10.

20. Set oscilloscope to 10 mV/div. Measure trace is t 3.2 divisions wide (32 mV,

90 dB).

21. Modify the equipment settings according to Table 14.

T able 14: Equipment Settings for X10, 100 kHz CMRR Checks

ADA400A Setting

Gain 10
Upper Bandwidth 1 MHz

Oscilloscope Setting

Vertical gain 20 mV/div
Time base 5 ms/div

Sine Wave Generator Setting

Output 100 kHz

22. Set ‘–’ input to GND.

23. Do steps 5 to 10 but with only one 10X attenuator.

24. Set oscilloscope to 1 mV/div. Measure trace is t 1 division wide (1 mV,

25. Modify the equipment settings according to Table 15.

ADA400A Differential Preamplifier

60 dB).

35

Performance Verification

T able 15: Equipment Settings for X10, 10 kHz CMRR Checks

ADA400A Setting

Upper Bandwidth 100 kHz

Oscilloscope Setting

Vertical gain 20 mV/div
Time base 50 ms/div

Sine Wave Generator Setting

Output 10 kHz

26. Set ‘–’ input to GND.

27. Do steps 5 to 10 but with only one 10X attenuator.

28. Set oscilloscope to 100 mV/div. Measure trace is t 0.56 division wide

(56 mV, 85 dB).

29. Modify the equipment settings according to Table 16.

T able 16: Equipment Settings for X10, 100 Hz CMRR Checks

ADA400A Setting

Upper Bandwidth 3 kHz

Oscilloscope Setting

Vertical gain 20 mV/div
Time base 5 ms/div

Sine Wave Generator Setting

Output 100 Hz

30. Set ‘–’ input to GND.

31. Do steps 5 to 10 but with only one 10X attenuator.

32. Set oscilloscope to 100 mV/div. Measure trace is t 0.56 division wide

(56 mV, 85 dB).

33. Disconnect setup.

36

This completes the performance verification procedure.

ADA400A Differential Preamplifier

WARNING

The following servicing instructions are for use only by qualified personnel. To
avoid injury, do not perform any servicing other than that stated in the operating
instructions unless you are qualified to do so. Refer to all safety summaries before
performing any service.

Adjustment Procedures

Use the procedures in this section to return the ADA400A Differential Preampli­fier to conformance with the Warranted Characteristics listed in the Specifica-
tions section on page 21.

Before performing any procedures in this section, please read the sections
entitled Requirements for Performance and Equipment Required.

Requirements for Performance

Before performing these procedures, please address the following requirements:

H You must be a trained service technician to perform this procedure.
H You must adjust the ADA400A Differential Preamplifier in an environment

in which temperature, altitude, humidity, and vibration are within the
operating limits described in Specifications.

H You must calibrate the ADA400A Differential Preamplifier at the center

temperature range of 22 ± 5_ C.

Equipment Required

H You must warm up the ADA400A Differential Preamplifier for at least 20

minutes prior to adjustment.

For a complete list of equipment required to perform the procedures in this
section, see the Equipment Required section under Performance Verification on
page 29.

ADA400A Differential Preamplifier

37

Adjustment Procedures

Procedure

Before you begin these procedures, remove the top housing using the procedure
on page 50. Leave the inner shield in place. See Figure 16 for a diagram of the
adjustment locations.

NOTE. To avoid contaminating the sensitive areas of the circuit board, do not
remove inner shield or touch the circuit board. Access all adjustments through
holes of inner shield

Connect the output of theADA400A Differential Preamplifier to the oscillo­scope, turn the oscilloscope on, and let the ADA400A warm up for 20 minutes.

NOTE. Before performing these procedures, make sure your oscilloscope can
display the proper scale factor. If you are using an oscilloscope that is not
compatible with the scale factor coding of the ADA400A Differential Preamplifi­er to perform these procedures, see page 2 to properly configure the scale factor
coding.

To convert the volts/division settings for oscilloscopes that cannot read the scale
factor from the ADA400A, multiply the volts/div setting in the procedure by the
gain setting of the ADA400A.

38

ADA400A Differential Preamplifier

Adjustment Procedures

CV14

(LF Compensation)

*CV13

R18

(HF CMRR)

*CV17

RV106

(10X Gain)

RV32

(Offset Zero)

CV6
(LF Compensation)

*CV12

*CV18

RV17
(LF CMRR)

CV4 (HF)

RV62
(100X Gain)

RV33
(Offset Balance)

Figure 16: Location of Adjustments Underneath Inner Shield

ADA400A Differential Preamplifier

*Factory adjust only

39

Adjustment Procedures

Gain Adjustments

Equipment
Required

One digitizing oscilloscope (item 1)
One dual input coupler (item 6)
One calibration generator (item 4)
One coaxial cable (item 9)
One adjustment tool (item 10)

1. Connect the ADA400A to Channel 1 and make the equipment settings

according to Table 17.

T able 17: Equipment Settings for Gain Adjustments

ADA400A Setting

+ Input DC
– Input Gnd
Gain 100
Upper Bandwidth 100 kHz
Offset Off

Oscilloscope Setting

Channel Selection Ch1
Vertical input impedance 1 MW
Vertical gain 10 mV/div
Time base 200 ms/div
Coupling DC
Vertical Position 0 V (mid-scale)
Trigger Edge
Trigger position 50%
Trigger source Ch4
Acquisition mode Hi Res
Auto Measurement Amplitude
Bandwidth Full

Calibration Generator Setting

Output 50 mV calibrated, 1 kHz

2. Connect a dual input connector to inputs of ADA400A.

3. Connect a coaxial cable from the output of the calibration generator to the

dual input connector.

40

ADA400A Differential Preamplifier

Adjustment Procedures

4. Adjust vertical position knob on the oscilloscope to center square wave on

screen.

5. Adjust RV62 for 5.0 divisions on screen (50 mV).

6. Set ADA400A gain setting to 10.

7. Set calibration generator to 0.5 V amplitude.

8. Adjust the vertical position knob on the oscilloscope to center square wave

on screen.

9. Adjust RV106 to 5.0 divisions.

Zero Offset Adjustments

Equipment
Required

One digitizing oscilloscope (item 1)

1. Connect the ADA400A to Channel 1 and make the equipment settings

according to Table 18.

T able 18: Equipment Settings for Offset Adjustments

ADA400A Setting

+ Input Gnd
– Input Gnd
Gain 10
Upper Bandwidth 100 Hz
Offset Off (remains off through out the test)

Oscilloscope Control Setting

Channel Selection Ch1
Vertical input impedance 1 MW
Vertical gain 500 mV/div
Time base 5 ms/div
Vertical Coupling DC
Vertical Position 0 V (mid-scale)
Trigger mode Auto
Acquisition mode Hi Res
Bandwidth Full

2. Check to make sure oscilloscope is at position 0 and vertical offset 0.

ADA400A Differential Preamplifier

41

Adjustment Procedures

3. Switch the gain setting between 10 and 100 while adjusting RV33 for

minimum shift in the oscilloscope trace.

a. Make note of trace position at gain setting of 10.
b. Switch gain setting to 100.
c. Adjust trace to where it was at the gain setting of 10.
d. Repeat steps a to c until there is a minimum amount of shift.

4. Adjust RV32 to center trace on screen.

5. Switch the gain setting from 0.1, 1, 10 and 100 and verify that trace does not

shift more than one division from center.

6. Disconnect setup.

LF CMRR Adjustments

Equipment
Required

One digitizing oscilloscope (item 1)
One sine wave generator (item 2)
One dual input coupler (item 6)
One 50 W terminator (item 7)
Two coaxial cables (item 9)
One adjustment tool (item 10)

1. Connect the ADA400A to Channel 1 and make the equipment settings

according to Table 19.

T able 19: Equipment Settings for Attenuator Balance Adjustments

ADA400A Setting

+ Input DC
– Input Gnd
Gain 1
Upper Bandwidth 100 Hz

Oscilloscope Setting

42

Vertical gain 1 V/div
Time base 20 ms/div
Trigger Source Ch4

Sine Wave Generator Setting

Output 10 Hz

ADA400A Differential Preamplifier

Adjustment Procedures

2. Connect dual input connector to inputs of ADA400A.

3. Connect 50 W terminator to dual input connector.

4. Connect a coaxial cable from sine wave generator output to 50 W terminator.

5. Connect another coaxial cable from trigger output of sine wave generator to

Ch4 of oscilloscope.

6. Adjust sine wave generator attenuator variable knob for 5 divisions (5 V) on

screen.

7. Set ADA400A ‘–’ input to DC.

8. Set oscilloscope volts/div to 1 mV.

9. Adjust RV17 for minimum signal amplitude.

10. Disconnect setup.

CMRR Adjustments

Equipment
Required

One digitizing oscilloscope (item 1)
One sine wave generator (item 2)
One dual input coupler (item 6)
One 50 W terminator (item 7)
Two 10X attenuators (item 8)
Two coaxial cables (item 9)
One adjustment tool (item 10)

1. Connect the ADA400A to Channel 1 and make the equipment settings

according to Table 20.

T able 20: Equipment Settings for CMRR Adjustments

ADA400A Setting

+ Input DC
– Input Gnd
Gain 100
Upper Bandwidth FULL (1 MHz)

Oscilloscope Setting

Vertical gain, Ch 1 2 mV/div
Time base 5.0 ms/div
Acquisition mode Average

ADA400A Differential Preamplifier

43

Adjustment Procedures

T able 20: Equipment Settings for CMRR Adjustments (Cont.)

Oscilloscope Setting

Number of waveforms to average 20
Trigger source Ch4

Sine Wave Generator Setting

Output 100 kHz, 1 Vp-p into 50 W

2. Connect a coaxial cable from trigger output of sine wave generator to Ch4 of

oscilloscope.

3. Connect dual input connector to inputs of ADA400A.

4. Connect 50 W terminator to dual input connector.

5. Connect two 10X attenuators to 50 W terminator.

6. Connect a coaxial cable from sine wave generator output to 10X attenuators.

LF Compensation

Adjustments

7. Adjust trigger level for a steady display.

8. Adjust amplitude for 5 divisions (10 mV) on screen.

9. Remove the two 10X attenuators and connect the cable directly to the 50 W

terminator.

10. Set ADA400A ‘–’ input to DC.

11. Set oscilloscope to 2 mV/div.

12. Adjust CV4 and R18 for minimum signal amplitude (≤ 1 mV).

13. Disconnect setup.

Equipment
Required

One digitizing oscilloscope (item 1)
One calibration generator (item 4)
One dual input coupler (item 6)
One 50 W terminator (item 7)
Two coaxial cables (item 9)
One adjustment tool (item 10)

44

1. Connect the ADA400A to Channel 1 and make the equipment settings

according to Table 21.

ADA400A Differential Preamplifier

T able 21: Equipment Settings for LF Adjustments

ADA400A Setting

+ Input DC
– Input Gnd
Gain 1
Upper Bandwidth Full (1 MHz)

Oscilloscope Setting

Vertical gain, Ch1 200 mV/div
Time base 20 ms/div

Calibration Generator Setting

Output Mode Fast Rise, 10 kHz

2. Connect dual input connector to ADA400A input.

Adjustment Procedures

3. Connect 50 W terminator to dual input connector.

4. Connect a coaxial cable to calibration generator fast rise output to 50 W

terminator.

5. Connect a coaxial cable from trigger out of calibration generator to Ch4 of

oscilloscope.

6. Adjust amplitude for 5 divisions on screen.

7. Adjust CV6 for flat response.

8. Make the second equipment settings according to Table 22.

T able 22: Second Equipment Settings for LF Adjustments

ADA400A Setting

+ Input DC
– Input DC

Oscilloscope Setting

Vertical gain 5 mV/div
Time base 20 ms/div

9. Adjust CV14 for minimum trace.

10. Disconnect setup.

This completes the ADA400A adjustment procedures.

ADA400A Differential Preamplifier

45

Adjustment Procedures

46

ADA400A Differential Preamplifier

Maintenance

Warranty Service

This section details the maintenance and replacement procedures for the
ADA400A Differential Preamplifier.

Tektronix warrants this product for three years from date of purchase. (A
complete warranty statement appears at the front of this manual.) Tektronix
provides warranty service at most Tektronix service locations worldwide. The
Tektronix product catalog lists all service locations worldwide.

Should the ADA400A Differential Preamplifier require replacement under terms
of the warranty, return the preamplifier to a Tektronix service center. Include the
following information: name of purchaser, return address, name and phone
number of a person that Tektronix may contact, date of purchase, and a
description of the defect.

In the U.S., call 1-800-TEK WIDE (1-800-835-9433) for further assistance.

Preparation

Before Servicing

Preventing ESD

This manual provides information for limited servicing of the ADA400A
Differential Preamplifier

NOTE. Only qualified service personnel should attempt any internal repair or
maintenance of the ADA400A Differential Preamplifier.

Before servicing the ADA400A Differential Preamplifier, please read the
General Safety Summary starting on page iii.

The ADA400A Differential Preamplifier contains internal components that are
susceptible to damage from electrostatic discharge (ESD).

ADA400A Differential Preamplifier

47

Maintenance

Cleaning

CAUTION. To prevent damaging internal components by means of electrostatic
discharge (ESD), perform all service at a static-free work station and wear a
grounded anti-static wrist strap.

Do not slide the internal module over any surface. Place internal module in
static-free bag for transportation away from work station.

To prevent damage to the ADA400A Differential Preamplifier, avoid using
chemicals that contain benzine, benzene, toluene, xylene, acetone, or similar
solvents.

Do not immerse the ADA400A Differential Preamplifier or use abrasive
cleaners.

Dirt on external surfaces may be removed with a soft cloth dampened with a
mild detergent and water solution, or isopropyl alcohol.

NOTE. Certain areas of the circuit board are sensitive to surface contamination.
Avoid touching the surfaces of the circuit board. Handle the circuit board by the
edges. If the circuit board is contaminated, wash the board with Isopropyl
Alcohol and rinse with warm deionized water.

Replacement Procedures

Refer to the procedures in this section before replacing any part on the
ADA400A Differential Preamplifier. For a list of all customer replaceable parts,
see the Replaceable Parts section that begins on page 55 and the exploded view
on page 59.

Replacing TEKPROBE

Interface Pins

Periodically check to see that each of the interface pins move freely and fully
extends out of the interface. If any pin fails to move freely and fully extend, it
should be replaced.

To remove a TEKPROBE interface pin, firmly grasp the pointed tip with pliers
and pull the pin out of the connector. See Figure 17.

No tools are required to install a replacement pin. Insert a new pin into the
connector socket as far as possible using finger pressure. If necessary, seat the
pin into the connector by pressing the tip gently but firmly against a hard
surface, such as a wood block or table top.

48

ADA400A Differential Preamplifier

Figure 17: Replacing TEKPROBE Interface Pins

Maintenance

Replacing the TEKPROBE

Interface Collar

To remove the TEKPROBE interface collar, firmly grasp the body of the output
head with one hand, and the TEKPROBE interface collar with the other hand.
Firmly pull the interface collar off.

To replace the collar, first note the pin configuration in the interface collar. The
group of three pins fit through the smaller of the two holes in the interface collar.
Align the tab to the slot and gently press the two pieces together. See Figure 18.

Once installed, the TEKPROBE collar should rotate freely to lock and unlock.

Tab

Slot

Figure 18: Replacing the TEKPROBE collar

ADA400A Differential Preamplifier

49

Maintenance

Replacing the Input Fuses

To remove and replace an input fuse, insert a flat-blade screwdriver into the slot
on the fuse cap, press in and turn counter clockwise to remove the fuse.

CAUTION. To properly protect the inputs of the ADA400A Differential Preamplifi­er, replace fuses with the type specified in the Replaceable Parts section.

Insert the replacement fuse into the cap on the fuse holder, insert, and use the
flat-blade screwdriver to press in and lock the fuse cap counterclockwise.

+ Input Fuse – Input Fuse

Figure 19: Input Connectors and Fuses

Accessing Internal

Components

Replacing the

Potentiometers

To access internal components of the ADA400A Differential Preamplifier, refer
to the exploded view, Figure 22, on page 59 and perform the following proce­dure:

1. Using a 1/16-inch Allen wrench, loosen the set screws on the COARSE and

FINE controls and remove the knobs.

2. Remove the four screws that hold the top housing, separate the top housing

from the bottom housing and set the top housing to one side.

STOP. If you intend to electrically adjust the ADA400A or move a jumper, do not
proceed further. The adjustments and jumpers are accessible through holes in the
circuit board shield. Proceed further only if you intend to replace parts under the
shield.

3. Following the static precautions presented at the beginning of this section,

remove the screws on the top of the shield and carefully lay the shield over
to the side without straining the wires of the potentiometers.

After performing the procedure to access the internal components of the
ADA400A Differential Preamplifier, replace one of the potentiometers as
follows:

50

ADA400A Differential Preamplifier

Maintenance

1. Unsolder the wires from the potentiometer.

2. Remove the nut on the shaft of the potentiometer and replace the potentiom-

eter with the new part. Replace and tighten the nut and washer on the shaft.

3. Resolder the wires as Figure 20 illustrates.

Replacing the Cable

Assembly

(Fine)

311–2533–00

Brown

Orange

Red

Orange

(Coarse)

311–2158–02

Brown

Red

Figure 20: Potentiometer Connections

After performing the procedure to access the internal components of the
ADA400A Differential Preamplifier, replace the cable assembly as follows:

1. Remove the remaining two screws that hold the circuit board to the bottom

NOTE. To prevent contaminating sensitive areas of the circuit board, handle the
circuit board by the edges only.

2. Unsolder the four colored wires from the top of the circuit board and the

3. Note the color-code information on the circuit board. Replace the cable

4. Place the circuit board and cable strain relief in the bottom housing and

ADA400A Differential Preamplifier

housing.

three ground prongs from the bottom of the circuit board.

assembly and solder the new wires.

reinstall hardware.

51

Maintenance

Replacement Parts

Theory of Operation

Refer to the Replaceable Parts section beginning on page 55 for a list of
customer replacement parts.

Figure 21 illustrates the functional blocks of circuitry from left to right in the
order of input to output. The darker boxes in the illustration designate front panel
controls and lines with arrows indicate the functional blocks that the controls
affect.

Input

ADA400A Differential Preamplifier

AC-GND-DC

+

–

Input Coupling/

Input Protection

1 M / 1 W

Select

High-Z

Attenuator

(1/1, 1/100)

Input Coupling/

Input Protection

AC-GND-DC

High-Impedance

Amplifier

+

–

Gain = X10

Gain .1, 1, 10, 100

DC

Offset

+

On/Off,

Coarse, Fine

Low-Z
Attenuator
(1/1, 1/10)

100 Hz, 3 kHz, 100 kHz 1 MHz

Scale Factor

Coding

Overrange

Detect

Output
Amplifier

Low-Pass

Filter

Gain = X10

Upper Bandwidth Select

TEKPROBE

Interface

50 W

Output
Cable

Oscilloscope

Signal Out

+15V
–15V

+5V

Data

Ground

Figure 21: Diagram of the ADA400A Differential Preamplifier

52

ADA400A Differential Preamplifier

Maintenance

Input Protection and

Coupling

Input Impedance

Attenuation and

Amplification

Any signals on the inputs of the ADA400A Differential Preamplifier must pass
through the input protection and coupling circuits.

Input Protection. The input protection circuit shunts excessively high-voltage
signals to ground and blows the protective fuse if the current exceeds 1/16 am­pere for any length of time.

Input Coupling. The coupling switch for a particular input selects one of the
following connections to the input of the preamplifier: AC, GND (ground), or
DC. For more information on these switch positions, see page 15.

Internal jumpers connect an input impedance of 1 MW in parallel with 55 pF.
With the jumpers disconnected the input impedance is virtually infinite (10
For more information about these jumpers, see page 12.

The gain switch sets the gain of the preamplifier by selecting the amount of
attenuation at two different points in the circuitry: 1/1 or 1/100 attenuation in the
high-impedance attenuator and 1/1 or 1/10 attenuation in the low-impedance
attenuator. The lowest gain setting, for example, selects the highest total amount
of attenuation.

12

W).

DC Offset

Low-Pass Filter

Overrange Detect

Scale-Factor Coding

TEKPROBE Interface

The offset controls adjust the DC component of the input signal. To keep the
signal from distorting, the signal must be within the dynamic range of the
amplifier. For more information on the dynamic range characteristic, refer to the
notes on page 16.

The Upper Bandwidth Control selects different RC networks in the low-pass
filter. The bandwidth settings are 100 Hz, 3 kHz, 100 kHz, and 1 MHz.

Should the input signal exceed the dynamic range of the output amplifier, the
overrange detection circuit activates the indicator on the front panel.

The gain switch also selects a resistance that appears on the data pin. If the host
oscilloscope is properly equipped (see Installation on page 2), this resistance
determines the vertical scale factor on the oscilloscope display.

The TEKPROBE interface provides power, signal, and data connections between
the ADA400A Differential Preamplifier and the oscilloscope.

ADA400A Differential Preamplifier

53

Maintenance

Troubleshooting

Table 23 lists symptoms of electrical faults, possible causes, and corrective
actions.

T able 23: Electrical Faults

Symptom Possible Cause Corrective Action(s)

No power Damage to TEKPROBE interface connec-

tions. Check interface pins and cable
assembly wires for damage.

No output signal on connector end of cable
assembly or output too high or low

Intermittent or difficult positioning Defective position controls Replace position control(s)
No signal output to cable assembly —

interface power is present and fuses are
not blown

Blown input fuse
Damage to output cable

Faulty module Send unit to service center for exchange or

Replace interface pin(s)
Replace or repair cable assembly

Check and replace fuse(s)
Repair or replace cable assembly

replacement.

Repackaging Instructions

If the original packaging is unfit for use or not available, use the following
packaging guidelines:

1. Use a corrugated cardboard shipping carton having inside dimensions at least

one inch greater than the probe dimensions. The box should have a carton
test strength of at least 200 pounds.

2. Put the probe into a plastic bag or wrap to protect it from dampness.

3. Place the probe into the box and stabilize it with light packing material.

54

4. Seal the carton with shipping tape.

ADA400A Differential Preamplifier

Replaceable Parts

This section contains a list of the replaceable modules for the ADA400A
Differential Preamplifier. Use this list to identify and order replacement parts.

Parts Ordering Information

Replacement parts are available through your local Tektronix field office or
representative.

Changes to Tektronix instruments are sometimes made to accommodate
improved components as they become available and to give you the benefit of
the latest circuit improvements. Therefore, when ordering parts, it is important to
include the following information in your order.

H Part number
H Instrument type or model number
H Instrument serial number
H Instrument modification number, if applicable

Module Servicing

If you order a part that has been replaced with a different or improved part, your
local Tektronix field office or representative will contact you concerning any
change in part number.

Change information, if any, is located at the rear of this manual.

Modules can be serviced by selecting one of the following options. Contact your
local Tektronix service center or representative for repair assistance.

Module Exchange. In some cases you may exchange your module for a reman­ufactured module. These modules cost significantly less than new modules and
meet the same factory specifications. For more information about the module
exchange program, call 1-800-TEK-WIDE, extension 6630.

New Modules. You may purchase replacement modules in the same way as other
replacement parts.

ADA400A Differential Preamplifier

55

Replaceable Parts

Using the Replaceable Parts List

This section contains a list of the mechanical and/or electrical components that
are replaceable for the ADA400A Differential Preamplifier. Use this list to
identify and order replacement parts. The following table describes each column
in the parts list.

Parts List Column Descriptions

Column Column Name Description

1 Figure & Index Number Items in this section are referenced by figure and index numbers to the exploded view

illustrations that follow.
2 Tektronix Part Number Use this part number when ordering replacement parts from Tektronix.
3 and 4 Serial Number Column three indicates the serial number at which the part was first effective. Column four

indicates the serial number at which the part was discontinued. No entries indicates the part is

good for all serial numbers.
5 Qty This indicates the quantity of parts used.
6 Name & Description An item name is separated from the description by a colon (:). Because of space limitations, an

item name may sometimes appear as incomplete. Use the U.S. Federal Catalog handbook

H6-1 for further item name identification.
7 Mfr. Code This indicates the code of the actual manufacturer of the part.
8 Mfr. Part Number This indicates the actual manufacturer’s or vendor’s part number.

Abbreviations

Mfr. Code to Manufacturer

Cross Index

Abbreviations conform to American National Standard ANSI Y1.1–1972.

The table titled Manufacturers Cross Index shows codes, names, and addresses
of manufacturers or vendors of components listed in the parts list.

56

ADA400A Differential Preamplifier

Replaceable Parts

Manufacturers Cross Index

Mfr.
Code

0JR05 TRIQUEST CORP 3000 LEWIS AND CLARK HWY VANCOUVER WA 98661–2999
0KB01 STAUFFER SUPPLY 810 SE SHERMAN PORTLAND OR 97214
18359 PYLON CO INC 51 NEWCOMB ST ATTLEBORO MA 02703–1403
22526 BERG ELECTRONICS INC (DUPONT) 857 OLD TRAIL RD ETTERS PA 17319
32997 BOURNS INC

61935 SCHURTER INC 1016 CLEGG COURT PETALUMA CA 94952–1152
71400 BUSSMANN

73743 FISCHER SPECIAL MFG CO 111 INDUSTRIAL RD COLD SPRING KY 41076–9749
78189 ILLINOIS TOOL WORKS INC

80009 TEKTRONIX INC 14150 SW KARL BRAUN DR

93907 TEXTRON INC

Manufacturer Address City, State, Zip Code

TRIMPOT DIV

DIV OF COOPER INDUSTRIES INC

SHAKEPROOF DIV

CAMCAR DIV

1200 COLUMBIA AVE RIVERSIDE CA 92507–2114

114 OLD STATE RD
PO BOX 14460

ST CHARLES ROAD ELGIN IL 60120

PO BOX 500
600 18TH AVE ROCKFORD IL 61108–5181

ST LOUIS MO 63178

BEAVERT ON OR 97077–0001

ADA400A Differential Preamplifier

57

Replaceable Parts

Replaceable Parts List

Fig. &
Index
Number

22–1 380–1098–00 1 HOUSING:TOP & BOTTOM,STEEL–ZINC PLATE 80009 380109800

–2 334–8900–00 1 MARKER,IDENT:INSTRUMENT LABEL 80009 334890000
–3 366–1861–03 2 KNOB:GREY,0.252 ID X 0.706 OD X0.612 H,

–4211–0541–00 4 SCREW,MACHINE:6–32 X 0.25,FLH,100 DEG,STL,CD PL,

–5 220–0495–00 2 NUT,PLAIN,HEX:0.375–32 X 0.438 HEX,BRS,CD PL 73743 ORDER BY DESC
–6 210–0012–00 2 WASHER,LOCK:0.384 ID,INTL,0.022 THK,STL 78189 1220–02–00–0541
–7 337–4037–00 1 SHIELD:0.040 STEEL,ZINC PLATE,7.5X 5.0 80009 337403700
–8311–2158–02 1 RES,VAR,WW:PNL,5K OHM,5%,1W 32997 84A1C–B24–J13
–9 –––––––––– 1 CIRCUIT BD ASSY:MAIN

–10 159–0024–00 2 FUSE,CARTRIDGE:3AG,0.062A,250V,0.3 SEC 71400 AGC 1/16
–11 200–2264–00 2 CAP,FUSEHOLDER:3AG FUSES 61935 FEK 031 1666
–12 131–0993–00 3 CONN,BOX:SHUNT ,;FEMALE,STR,1 X 2,0.1 CTR,

–13 220–0497–00 2 NUT,PLAIN,HEX:0.5–28 X 0.562 HEX,BRS CD PL 73743 ORDER BY DESC
–14 210–0986–00 2 WASHER,FLAT:0.5 ID X 0.672 OD X 0.035,STL CD PL 80009 210098600
–15 211–0711–00 4 SCR,ASSEM WSHR:6–32 X 0.250,PNH,STL,CDPL,

–16 210–1039–00 2 WASHER,LOCK:0.521 ID,INT ,0.025 THK,SST 0KB01 1224–02–00–541
–17 348–0187–00 4 FOOT,CABINET:BLACK POLYURETHANE 80009 348018700
–18 211–0408–00 1 SCR,ASSEM WSHR:4–40 X 0.250,PNH,STL,CDPL,

–19 131–3627–01 7 CONTACT,ELEC:GOLD PLATED TIP

–20 205–0191–00 1 SHELL,ELEC CONN:BNC,ABS,DOVE GRAY

–21 174–3462–01 1 CABLE ASSY:CABLE W/COMP BOX 80009 174346201
–22 311–2533–00 1 RES,VAR,P ANEL:CERMET;50K OHM,10%,1.0W,LINEAR

–23 210–0004–00 5 WASHER,LOCK:#4 INTL,0.015 THK,STL 78189 1204–00–00–0541
–24 211–0394–00

Tektronix Part
Number

Serial No.
Effective

Serial No.

Discont’d

Qty Name & Description

W/SET SCREWS

POZ

(EXCHANGE ONLY)

0.385 H,30 GOLD,BLACK,JUMPER
(SUBPAR T OF 22–9)

T–15 TORX DR,MACHINE

T–10 TORX DR

(SUBPAR T OF 22–21)

(SUBPAR T OF 22–21)

TAPER,12.5 MM SQ,0.375DIA X 0.375 L BUSHING,
SOLDER LUGS

5

SCREW,MACHINE:4–40 X 0.875,PNH,STL CD PL TORX,
T10

Mfr.
Code

80009 366186103

80009 211054100

22526 65474–006

0KB01 ORDER BY DESC

0KB01 211–0408–00

18359 P–6158–1

80009 205019100

32997 53AAA–B24–A18R7

93907

Mfr. Part Number

B20–69595–003

58

159–0024–00
070–9164–xx

P6101B

STANDARD ACCESSORIES

2

FUSE,CARTRIDGE:3AG,0.062A,250V,0.3SEC

1

MANUAL,TECH:INSTRUCTION,ADA400A,DP

OPTIONAL ACCESSORIES

1

PROBE,PASSIVE:15MHZ 1X 2.0M

71400
80009

80009

AGC 1/16
0709164xx

P6101B

ADA400A Differential Preamplifier

Replaceable Parts

3

2

1

4

5
6

5
6

24
23

7

8
9

11

10

19

21

20

18

22

17

15

12

13

14

16

1

Figure 22: ADA400A Differential Preamplifier — Exploded View

ADA400A Differential Preamplifier

59

Replaceable Parts

60

ADA400A Differential Preamplifier

Glossary

Alternating Current (AC)

An electric current whose instantaneous value and direction change
periodically.

Amplitude

The difference between a high and a low point on a waveform. Signal
amplitude can be measured in terms of “peak-to-peak” or “peak” for
example.

Attenuation

The degree the amplitude of a signal is reduced when it passes through an
attenuating device such as a probe or attenuator. That is, the ratio of the input
measure to the output measure. For example, a 10X attenuator will attenuate,
or reduce, the input voltage of a signal by a factor of 10.

Bandwidth

Bandwidth is the specified frequency range of the vertical system wherein
the vertical response is greater than or equal to 0.707 (–3dB) of the specified
frequency down to DC or 0 Hz.

Common mode

Signals on both preamplifier inputs that are identical in voltage and phase.

Common-Mode Rejection Ratio (CMRR)

The extent to which a differential amplifier rejects a common-mode voltage
presented on the inputs. CMRR is the ratio of the differential gain to the
common-mode gain and is usually expressed in decibels (dB).

Coupling

The method of connecting the input circuit to the signal source. A coupling
circuit, for example, may pass only AC signals above a certain frequency.

Differential

Signals that are not identical in amplitude or phase and thereby present a
difference on the inputs of the preamplifier.

Direct Current

An electric current that flows in only one direction with essentially constant
value.

Frequency

A timing measurement that is the reciprocal of the period. Frequency is
measured in Hertz (Hz) where 1 Hz = 1 cycle per second.

Floating

A signal or voltage that does not have a reference to ground.

ADA400A Differential Preamplifier

61

Glossary

Gain

Increase in signal strength.

Ground

A connection or reference to the zero voltage potential of earth ground.

Ground loop

Two or more paths between grounded points in a circuit in which a current
circulates. This current may induce a voltage potential which corrupts
sensitive measurements.

Hertz

The unit of frequency, one cycle per second.

Megahertz (MHz)

6

A frequency of one million Hz (cycles per second), or 10

Hz.

Noise

An unwanted voltage or current in an electrical signal.

Normal mode

The signal of interest without the common-mode element.

Peak

The difference in amplitude between the maximum value and the average or
mean value of a waveform.

Peak-to-Peak

Amplitude measurement of the absolute difference between the maximum
and minimum amplitude.

Period

A timing measurement of the time covered by one complete signal cycle. It
is the reciprocal of frequency and is measured in seconds.

Phase

A timing measurement between two waveforms of the amount one leads or
lags the other. Phase is expressed in degrees where 360_ comprises one
complete cycle of one of the waveforms.

62

RMS

Amplitude (voltage) measurement of the true Root-Mean-Square voltage.

Single ended

A connection to one input of the preamplifier only. The coupling of the other
side must be set to ground (GND).

Waveform

The shape or form (visible representation) of a signal expressed as amplitude
versus time (Y-T).

ADA400A Differential Preamplifier

Index

A

accessories

recommended, 2
standard, 1

adjustment procedures, 37

CMRR, 43
equipment required, 29
gain, 40
LF CMRR, 42
LF compensation, 44
zero offset, 41

B

bandwidth limit, 18, 53
block diagram, 52

C

cable housing, procedure for replacing, 51
checks, functional, 4
cleaning, 48
clipping, 16
common-mode rejection, 14
connections

differential, 14
input, 11–15

single-ended, 13
connectors, illustrated, 8
controls

offset, 18, 53

overview , 7–10
cover, procedure for removing, 50

D

F

fuses, 50

location of, 8

G

gain, 16, 53
ground loops, 15

H

housing, procedure for removing, 50

I

input

common-mode range, 16
differential range, 16

input coupling, 15, 53

oscilloscope, 4, 15
precharging, 16

input impedance

oscilloscope, 4, 15

preamplifier, 12, 53
input protection, 53
input range, 16
installation, 2
interference, 19

J

jumper

input impedance, 12

scale-factor coding, 2

diagnostic procedures, 54

E

effective volts/division, 10
electrostatic discharge, preventing, 47

ADA400A Differential Preamplifier

M

maintenance, 47–54

O

offset range, 16
overrange detection circuit, 53
overrange indicator, 9, 16

63

Index

P

parts

list of replaceable, 55–60
replacement of. See Maintenance

performance verification, 29

CMRR, 33
equipment required, 29
gain, 31

input resistance, 31
potentiometers, procedure for replacing, 50
procedures, performance verification, 29

R

repackaging, 54
replacement procedures, 48

S

safety , general summary, iii
scale-factor coding, 53
shield, procedure for removing, 50
signal distortion, 16

T

TEKPROBE interface, 53

installation, 2
replacing interface collar, 49
replacing pins, 48

troubleshooting, 54

W

warranty service, 47

64

ADA400A Differential Preamplifier