Aphex 207D User Manual
Solution Delivery Series
two channel tube mic And
Instrument preamplier
Instruction Manual
207d
w i t h 2 4 - B i t 9 6 k H z A D C
P/N 999-4260
Revision 1
Released 02/04/2005
Manufactured by
Aphex Systems Ltd.
11068 Randall St.
Sun Valley, CA 91352
USA
S Y S T E M S
Copyright 2004 Aphex Systems Ltd. All rights reserved.
Produced by: Donn Werrbach. Creation tool: Adobe InDesign 2.0
207d
Dear Aphex Customer,
We are pleased to present the Model 207D Tube Microphone and Instrument Preamplifier with analog and digital
outputs. This continues the commitment made in all the products in our Solution Delivery Series- high performance audio;
extensive, useful and unique features; attractive and clean front panel design; and cost effective pricing.
Rather than being locked into a channel strip that has many functions but does few or none well, the Model 207D gets
you the best possible preamplifier and the freedom to choose the best processing for your application. Loop the output
of the processing back into the insert of the 207D and you have a complete front end without any compromises.
As with all our products, we are very proud of the ingenuity of design and the manufacturing quality of the Model 207D.
We love to hear from you, our customers, about your experiences with any of our products. Our customer support is
unmatched in the industry, so please do not hesitate to contact us.
Sincerely,
Marvin Caesar
instruction Manual
A MESSAGE FROM THE PRESIDENT
Safety Declarations
CAUTION: For protection against electric shock, do not remove the cover. No user serviceable parts inside.
WARNING: This equipment has been tested and found to comply with the limits for a Class A digital device pursuant to
Part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference when
the equipment is operated in a commercial environment. This equipment generates, uses, and can radiate radio frequency
energy and, if not installed and used in accordance with the operating guide, may cause interference to radio communications. Operation of this equipment in a residential area is likely to cause interference in which case the user will be required
to correct the interference at his own expense.
The user is cautioned that changes and modifications made to the equipment without approval of the manufacturer could
void the user’s authority to operate this equipment.
It is suggested that the user use only shielded and grounded cables to ensure compliance with FCC Rules.
|
Aphex Systems Ltd. Model 207DPage 2
Copyright 2001 by Aphex Systems, LTD. All rights reserved. All Aphex products are trademarks or registered trademarks of Aphex Systems,
LTD. Other brand and product names are trademarks or registered trademarks of their respective holders.
2-ch tube mic preamp with adc
207d
Table of Contents
1.0 CONTROLS & INDICATORS PLUS QUICK SETUP........................................................................
2.0 INTRODUCTION
2.1 What Distinguishes the Model 207D.....................................................................................
2.2 What Does the Tube Add? ..................................................................................................
2.3 What Else Is So Special? ......................................................................................................
2.4 What About The Digital Audio? ..........................................................................................
2.5 Block Diagram .....................................................................................................................
3.0 INSTALLATION AND INTERFACING
3.1 Installation ..........................................................................................................................
3.2 Rear Panel View ..................................................................................................................
3.3 AC Line Connection ............................................................................................................
3.4 Mic Input Connections .........................................................................................................
3.5 Instrument Inputs ...............................................................................................................
3.6 Insert jack ...........................................................................................................................
3.7 Output Connectors ..............................................................................................................
3.8 Operating Level Switch .......................................................................................................
3.9 Output Match ....................................................................................................................
3.10 Output Trim .......................................................................................................................
3.11 Digital Outputs (AES3 and S/PDIF) ......................................................................................
4.0 USING THE 207D
4.1 Split Independent Preamp Sections .....................................................................................
4.2 Using the Instrument Input .................................................................................................
4.3 Using the Microphone Input ................................................................................................
4.3.1 Using Phantom Power ........................................................................................
4.3.2 Using the Polarity Switch ...................................................................................
4.3.3 Using the Pad ....................................................................................................
4.3.4 Using Low Cut ...................................................................................................
4.3.5 Using MicLim™ .................................................................................................
4.4 Using Word Clock ................................................................................................................
4.4.1 External WC .......................................................................................................
4.4.2 Internal WC .......................................................................................................
4.5 Using Digital Audio (S/PDIF Output) ....................................................................................
4.6 Replacing Your Console’s Mic Preamps .................................................................................
4.7 Bypassing the Console Altogether ........................................................................................
4.8 Using the 207 for Stereo Recordings ...................................................................................
4.8.1 Spaced Pair Technique .......................................................................................
4.8.2 X-Y Technique ....................................................................................................
4.8.3 M-S Technique ..................................................................................................
. 4.8.4 Binaural Technique ............................................................................................
4.8.5 Further Reading .................................................................................................
5.0 WARRANTY AND SERVICE
5.1 Limited Warranty ................................................................................................................
5.2 Service Information .............................................................................................................
6.0 SPECIFICATIONS
6.1 General Specifications .........................................................................................................
6.2 Architectural Specifications .................................................................................................
7.0 APPENDICES
Appendix A - Introduction to Balanced and Unbalanced Wiring .................................................
Appendix B - Dealing With Ground and Hum ............................................................................
Appendix C - Proper Wiring Techniques ......................................................................................
Appendix D - Standard Cable Wiring ........................................................................................
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Page 3Aphex Systems Ltd. Model 207D
207d
instruction Manual
1.0 Controls and Indicators with Quick Setup
POWER ON
When the unit is turned on, audio is not passed
through to the output for a few moments while the
tube warms up. During the warm-up time, the power
indicator is yellow. When the power indicator turns
green, the audio will pass through to the output. This
protects you from heavy turn-on thumps.
MICROPHONES
You can use any type of balanced, low impedance
microphone from dynamics to ribbons to condensers. The 207D supplies a very clean and stable 48V
phantom voltage source suitable for even the most
expensive microphones. Phantom voltage is separately selectable on or off for each channel at the
front panel.
OUTPUTS
The two outputs can be used at the same time. They
are not fully isolated from each other, however. To
unbalance the XLR output, simply use pin 2 (high)
and pin 1 (ground) leaving pin 3 either grounded or
floating. You may ground the ring of the phone jack,
as will happen when you plug in a mono style phone
plug. The XLR output will still remain balanced. The
output impedance of the XLR jack is low enough to
optimally drive loads of 600 ohms and higher. It is
designed to interface with fully professional balanced
gear. The phone jack output impedance is significantly higher but meets the requirements for driving
typical semi-pro (“prosumer”) balanced and unbal-
anced equipment.
INSERT JACK
This allows you to insert any kind of line level equipment into the signal path between the 207D’s frontend preamps (mic and instrument) and tube output
stage. The operating level at this jack is in the vicinity
of IHF level (-10dBV). You should set up your inserted
outboard gear for -10dBV I/O sensitivity. All Aphex
processors can be readily set to operate at this level.
HEADROOM METER
As the level approaches 0dB, you run out of headroom and the output will go into clipping unless
MicLim is turned on. There is a span of 27dB indicated, so you can watch your signal level for safety
and convenience. When MicLim is on, the peak level
will be held to about 3dB under clip for over-level
inputs rising as much as 20dB beyond the normal
overload point.
INSTRUMENT INPUT
This input is available at the front panel through a
quarter inch phone jack. The input impedance is 1
megohms to match all coil type pickups and all powered pickups. Fully passive piezo pickups will work,
but may not deliver full tone. High impedance unbalanced microphones will usually work extremely well
with this input. When a plug is inserted, the mic
input is inoperative.
POWER INDICATOR
Aphex logo glows yellow when
power is first turned on. After a
minute of tube warm-up time, the
light turns green to indicate the
output is enabled.
PHANTOM
Switches the +48V
phantom power to
the microphone jack
on or off.
POLARITY
Inverts the relative
polarity (phase) of
the mic and instrument inputs.
PAD
Inserts 20dB of loss
at mic and instrument inputs, allowing for excessively
high levels.
Aphex Systems Ltd. Model 207DPage 4
LOW CUT
Switches on the
70Hz Low Cut filter.
Affects mic and
instrument inputs.
2-ch tube mic preamp with adc
MIC INPUT
DO NOT feed
mic inputs
OUTPUTS
INSERT
CHANNEL 1
-10 +4
Pin1 = Sleeve = GND, Pin 2 = Tip = HI, Pin 3 = Ring = LO
OPERATING
LEVEL
S Y S T E M S
AES3 OUT
SPDIF CLOCK IN
MODEL 207D 2 CHANNEL MIC PRE 24/96
207d
Quick Setup
OPERATING LEVEL
This adapts the model 207D’s internal dynamic
range to match either professional balanced equipment or semi-professional unbalanced equipment at
the output. It controls both output jacks. Both jacks
supply the same output level. Set as needed.
DIGITAL AUDIO
In external sync mode, the 207D locks up to frequencies between 32 and 96kHz. The push button located
in the meter window toggles the operating mode
among the internal frequency modes and external
sync. The AES3 and S/PDIF outputs will properly interface with all standard inputs. Follow the procedures
recommended in this manual for proper installation
and use.
OUTPUT HEADROOM METER
Indicates the available headroom in decibels
below clipping. At 0dB the output level reaches
the maximum level available at all outputs
depending upon the Output Trim and Operating Level settings.
Phantom Powered
“Y” CABLE
See Apdx D
OUT
Line Level
Processor,
Compressor, EQ
Standard Hookup to Rear Panel
ONE CHANNEL SHOWN
Mic Source
Passive or
Use high quality balanced mic cables.
Select the correct OPERATING LEVEL to most
closely match your
i.e.,
receiving equipment’s
input sensitivity.
IN
To Inputs of
Line Level Devices.
DO NOT Connect to Mic
Level Inputs!*
Use balanced or unbalanced cables as
needed. Consult Appendix D for wiring
options.
Digital Audio Interface
AES3 and S/PDIF
T
External
Word Clock
Input
*Why You Shouldn’t Connect a 207D’s Output to a Mic Level Input. The bottom line: you will get a lot of noise and possibly a
lot of distortion. The Model 207 is designed to generate a line level output from a mic level input. It optimizes the signal to noise ratio by
giving you a strong signal far above the preamplifier’s basic self noise level. This strong output signal can be up to 65dB higher than the
mic signal. It is perfect in level for a standard line input of a mixer or console. However, it will overload a mic input. If you turn down the
207’s gain to reduce its output low enough to stop overloading the mic input of your mixer, then your large console gain amplifies the
basic noise floor of the 207. That will result in a very poor signal to noise ratio. Always use the most gain possible in the 207 and adjust
your mixer’s fader or line input gain to accept it, and never feed a mic input from a 207D.
INSTRUMENT INPUT JACK
Input impedance is 1 megohm to
properly accept 99% of all music
instrument pickups. It is not designed
to receive extremely high impedance
non powered piezo pickups, however.
MicLim™
Switches on the
MicLim operating
mode. Use is always
recommended.
Switch off mainly for
testing.
LIMITING LED
Shows when MicLim is
working.
GAIN
Adjusts the microphone preamplifier and instrument gain.
OUTPUT TRIM
Screwdriver adjustable, works
with the rear panel OPERATING
LEVEL switch to calibrate the
207’s output level to precisely
match external equipment.
Page 5Aphex Systems Ltd. Model 207D
207d
2.0 Introduction
instruction Manual
2.1 WHAT DISTINGUISHES THE MODEL 207D
There are certainly a lot of mic preamps available
in the world. It seems that every audio equipment
company has at least one model to offer. A study
of currently available products shows that a large
percentage use similar circuits based on one or two
popular commercial i.c. chips. The basic design has
been done by the chip maker and the chips do a
competent job. We could have brought out such a
“me too” design, but it is important to Aphex that we
offer products that are more than just “competent”.
They must also be different and better. That is why
we did not introduce our first mic preamp until we
invented something that would make all the difference.
That invention turned out to be a new and unique
way to use a vacuum tube in a circuit that yields the
clear and detailed tube sound yet has none of the
limitations of conventional tube circuitry like short
life, noise, heat, and low bandwidth. That invention
is called the Reflected Plate Amplifier (RPA), and was
granted U.S. Patent #5,450,038. We introduced our
first microphone preamplifier incorporating the RPA,
the Model 107, in 1996 and it soon became one of
the most popular mic preamps in the world. People
appreciated the difference it made in the quality of
their work. Tens of thousands of 2-channel units were
sold.
More recently, we came up with another invention
pertaining to mic preamps. We had the idea that if
we could build a mic preamp that not only sounded
great, but also had a way to automatically prevent
input overloading over a significant dynamic range
above normal clipping, then we would have another
innovative hit on our hands. Many months of research
went into inventing a method to achieve this goal.
When we succeeded, we called it MicLim™. Later,
we introduced the Aphex Model 1788 Remote Controlled Mic Preamp including the MicLim™ feature.
Months of trials proved it to be extremely useful in live
sound reinforcement applications. Additional testing
showed it is also useful in recording. When we next
introduced our very high-end Aphex Thermionics™
Model 1100 Thermionic Mic Preamp, we included
the MicLim™ feature and it has received high acclaim
among some of the world’s top sound engineers.
Meanwhile, our Model 107 remained a solid product in the marketplace because of its low cost, high
performance and value. However, after enjoying
many years of sales, we thought we owed it to the
world to update the Model 107 with the new things
we have learned and developed since its inception.
Hence, the 207 was born. Production of the Model
107 was discontinued. In the present configuration,
a digital output is added and the model updated to
the 207D.
In addition to improving on the Model 107, the
Model 207D is a whole new product. We transported
the front-end and RPA components that characterize the sound of the 107 but we completely revised
our thinking about every other detail. We added the
MicLim™ feature and a professional quality instrument input. We even added a processing insert jack
so you can insert EQ, gating, or compression after
preamplification but before the tube output stage.
In this way you always get the sonic benefits of the
tube. We created a totally new and attractive style
for the chassis and panel that makes it look as great
as it performs.
With the Model 207D you are getting exclusive
Aphex design advantages and legendary sonic quality
at a very modest price. We hope you enjoy using it for
many years to come.
2.2 WHAT DOES THE TUBE ADD?
The Model 207D uses a discrete solid-state
transformerless front end carefully crafted for
extremely low noise and high common mode rejection. It runs without feedback, making it nearly ideal
as an input stage, never reflecting any feedback current back out to the microphone. Certainly, the input
stage has a measurable distortion level, but it is very
low and does not impart any appreciable tonality. The
tonality for which our tube preamplifiers are famous
is due exclusively to the tube.
Our unique and stable RPA tube circuit retains the
tube’s transconductance and grid characteristics
while at the same time creating a much more efficient amplifier stage that runs on low power supply
voltages. We designed the RPA in the Model 207D
to deliver a specific tube distortion curve that subtly
“voices” the preamp. If you have been using the
Model 207D or its predecessor, the Model 107, then
you know what that means. The preamp is characterized by most users as very transparent and detailed,
but not colored. The beauty of tubes is that their dis-
Aphex Systems Ltd. Model 207DPage 6
2-ch tube mic preamp with adc
207d
Introduction
tortion is so natural. The very slight tube distortion of
the Model 207D comprises typically less than 0.02%
of second order harmonics at average levels. What
is even more interesting is that this curve follows
the tube’s law as regards level, and furthermore, it
responds to certain very subtle dynamic space-charge
effects known only in tube amplifiers. Thus, the
sound with an RPA can have a large and open feeling
that is very natural and transparent.
2.3 WHAT ELSE IS SO SPECIAL?
It may sound trite, but everything else about the
Model 207D is special. When we designed its circuitry
and decided upon its features, we took into consideration a very wide range of factors. We “blocked in”
the things that our marketing experts wanted, but
then made sure that every circuit and feature could
work in harmony. Some things were discarded by
engineering because they would have compromised
the sound. Once we had the Model 207D very well
defined, we went to work at embodying the circuits
cleanly and cleverly, using some great ideas from the
Model 107, but redesigning most of it from scratch
through computer modeling and simulation and
finally through actual physical prototypes and listening sessions. There are no databook or textbook preamplifier circuits in the 207D. It’s all Aphex.
That being said, let us point out just a few of the
things that are special about the Model 207D. Then,
as you read more of this manual, you will gain appreciation for many other special aspects of this product.
First, let’s look at the front end. Other preamps, even
those costing many times more, pass the mic signal
through switch contacts to enact the pad and polarity features. This eventually leads to contact distortion
creeping into the sound because switch contacts will
eventually oxidize and, in the very least, need to be
operated frequently to keep themselves clean. That is
a big problem, especially for fixed installations where
it is impossible to exercise all the switches regularly
(daily?).
We used expensive d.c. operated, sealed, bifurcated
gold contact relays to switch these functions. These
relays never oxidize and can remain stationary for
many years without contact distortion.
not just rumble cutting. We very slightly peaked the
response at 120Hz by about 1dB so there will be a
natural phase compensation effect in the important
low-mid bass region helping regain a greater sense
of bass presence. That benefit is immediately apparent to experienced mic preamp users. We received so
much praise for this type of filter in the Model 107,
that we kept it for the 207D.
Just one more mention. Let’s look at the RPA tube
output stage. Here, we merge a real operating
vacuum tube into the world of semiconductors. The
tube serves as the main gain element and brings
us all of its warmth and clarity while remaining
directly linked to its solid-state support unit. There
are no transformers or high voltage supplies, yet the
strength of the output signal is more than powerful
enough to drive any practical load to full professional
levels with ease. Because of the unique capabilities
of the RPA circuit, we were able to mix the mic and
instrument signals directly to the tube without any
interaction. The result is exceptionally high performance.
2.4 WHAT ABOUT THE DIGITAL AUDIO?
With the superb audio quality of the 207D, it is obvious that only a high grade ADC will be able to capture
that quality and bring it into the digital domain. We
incorporated a 24 bit ADC that has a digital dynamic
range greater than the analog circuitry. In this way,
perfect dithering will be provided by the analog noise
floor. That is the most ideal form of dither since it
avoids the harshness of digitally synthesized dither
noise.
The AES3 and S/PDIF digital audio outputs are of 24Bit resolution. The analog noise floor, even though
exceptionally low in level for a mic preamp, will
typically dither the 24 bits into the 16-bit level which
makes it suitable for all projects, including anything
that will eventually end up on CD. Even if your digital
studio truncates the audio word length to 16-Bits,
the 207D’s natural dither will still make it sound
great.
Next, let’s look at the low cut filter. It is a second
order active filter that is designed for musicality,
Page 7Aphex Systems Ltd. Model 207D
207d
Introduction
XLR-3M
OUTPUT
instruction Manual
AES3
OUTPUT
1/4” PHONE
PAD
LEVEL
OPERATING
+4dBu | -10dBV
OUTPUT
S/PDIF
OUTPUT
WORD CLOCK
INPUT
RPA DISCRETE
INSERT JACK
1/4” TRS PHONE
NPN
DISCRETE
FRONT END
TRIM
OUTPUT
TUBE AMPLIFIER
GAIN
PAD
FILTER
LOW CUT
DRIVER
LDR
MiCLiM™
METER
OUTPUT
HEADROOM
MiCLiM™
CONTROL
ADC
FROM OTHER CHANNEL
ONE CHANNEL SHOWN
POWER
SWITCHED
+48V PHANTOM
2.5 SIMPLIFIED BLOCK DIAGRAM
POLARITY
MIC/INST
AUTOSWITCH
XLR-3F
MIC INPUT
FET
HI-Z INSTRUMENT
1/4” PHONE INPUT
PREAMP
Aphex Systems Ltd. Model 207DPage 8
2-ch tube mic preamp with adc
MIC INPUT
DO NOT feed
mic inputs
PROTECTED UNDER
US PATENT
5,450,038
APHEX AND MICLIM
ARE REGISTERED
TRADEMARKS OF
APHEX SYSTEMS LTD.
OUTPUTS
INSERT
CHANNEL 2
-10 +4
Pin1 = Sleeve = GND, Pin 2 = Tip = HI, Pin 3 = Ring = LO
OPERATING
LEVEL
MIC INPUT
DO NOT feed
mic inputs
OUTPUTS
INSERT
CHANNEL 1
-10 +4
Pin1 = Sleeve = GND, Pin 2 = Tip = HI, Pin 3 = Ring = LO
OPERATING
LEVEL
100-240V 0.12-0.05A 50/60Hz
S Y S T E M S
|
AES3 OUT
SPDIF CLOCK IN
MADE
IN
U.
S.A.
MODEL 207D 2 CHANNEL MIC PRE 24/96
207d
3.0 Installation & Interfacing
3.1 INSTALLATION
The Model 207D occupies a single rack space (45mm or 1-3/4 inches) of a standard EIA equipment rack.
When rack mounting, use appropriate cushioned rack screws. Never restrict air flow through the device’s vents.
When installing the units into a rack, distribute the units evenly. Otherwise, hazardous conditions may be created by an uneven weight distribution. Connect the unit only to a properly rated supply circuit. Reliable earthing (grounding) of rack mounted equipment should be maintained. Try not to position the 204 directly above
devices that generate excessive heat such as power amplifiers (unless adequately ventilated) or near equipment
with heavy transformer hum fields.
3.2 REAR PANEL VIEW
3.3 AC LINE CONNECTION
Use only a power cord that carries approvals for use in your location. The 207D’s internal power supply is
designed to operate from all nominal power sources from 100 to 240 volts a.c. at 50/60Hz without requiring
the user to change any settings. In case of failure, do not attempt to change the internal fuse because it will
never blow unless the power supply fails catastrophically. The power supply will need to be serviced by a competent service technician in such a case.
R
3.4 MIC INPUT CONNECTIONS
The MICROPHONE input connectors are located on
the rear panel. They are the standard XLR-3F type.
Use only properly wired balanced mic cables.
PROPER MICROPHONE CABLE WIRING
Female XLR Male XLR
CAUTION: Beware that 48 volt PHANTOM POWER
may be applied to either or both of the microphone inputs, creating a potential shock hazard.
Standard practice dictates shutting off the phantom power before plugging or unplugging microphones. Wait at least 10 seconds for the voltage
to fall sufficiently. This is not only for safety, but
for protection of sensitive microphones against
power inrush.
3.5 INSTRUMENT INPUTS
The INSTRUMENT inputs are located on the front
panel providing a high input impedance of 1
megohms. The instrument jack accepts standard
1/4” phone plug music instrument cords (i.e., guitar
cords). This input is also suitable for high impedance microphones having cables with 1/4” phone
plugs. The do-it-yourselfer can refer to appendix D
for numerous examples of proper cable and plug
wiring.
3.6 INSERT JACK
The Model 207D allows you to insert additional
signal processing between the mic preamp’s front
end stage and the tube output stage. This is clearly
shown in the 207D’s block diagram at left. The interconnect is unbalanced by way of a stereo (TRS) I/O
jack on the rear panel. You will need a conventional
“Y” cable to interface with external equipment. Such
cables are available commercially. Make sure you
have the correct cable: tip is send, ring is receive, and
sleeve is ground. Check the following chart. Nominal
level is -10dBV.
3.7 OUTPUT CONNECTORS
The output connectors are located on the rear panel.
There are two output connectors per channel, one
1/4” TRS phone type and one XLR-3M type. They
Page 9Aphex Systems Ltd. Model 207D
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