Kenwood AG-203 Service manual

Trio

AG-203

CR Oscillator

Instruction Manual

Contents

Features 3
Specifications 4
Circuit Description 6
Panel Controls and Their Functions 8
Operating Instructions 10
Applications 12
Maintenance 15
Adjustment 16
Caution 17
Parts List 18
PC Board 21
Schematic Diagram 22

Features

• All solid-state circuitry ensure extreme high stability, minimum warm-up time
and less power consumption.

• High reliability with adoption of direct coupled circuits throughout the entire
stage.

• Compact styling with vertical type panel for easy operation.

• Frequency dial scale calibrated with single-scale graduations for frequency

range 10Hz to 1MHz selectable in 5 ranges.

• High output design; more than 7V rms at no load and more than 3.5V rms at
600Ω. Output level is fully adjustable with a 10dB step, 6 range attenuator and
a level indicator.

• Low output impedance of 600Ω. The attenuator provides accuracy of ±1dB at
600Ω load.

• Sine and Square waves easily available.

• Synchronizing input terminal.

• Extremely high stability against variation of power source.

Specifications

Frequency Range

Frequency accuracy

(Sine Wave Characteristics)

Output voltages (no-load)

Frequency Characteristics

(reference freq. 1KHz)

Distortion Factor

(Square wave characteristic)

Output Voltage (no load)

Sag:
Rise and Fall times:
Overshoot:
Duty ratio:

(External Synchronization Characteristics)

Synchronization range:
Max, allowable input voltage:
Input impedance:
Output impedance:
Output attenuator:

(Stability against power source voltage variation (with respect to
variation of 100V ±10%))

Frequency drift:
Output Voltage Variation:
Operating Temperature:

Power Requirements:

Power Consumption:
External View:
Dimensions:

x 1 range; 10Hz – 100Hz
x 10 range; 100Hz – 1KHz
x100 range; 1KHz – 10KHz
x 1K range; 10KHz – 100KHz
x 10K range; 100KHz – 1MHz

±(3% ±1Hz)

7V rms or more

10Hz – 1MHz, ±1dB

400Hz – 20KHz, 0.1% or less
100Hz – 100KHz, 0.3% or
less (x 10 range for 100Hz)
50Hz – 200KHz, 0.5% or less
20Hz – 500KHz, 1% or less
10Hz – 1MHz, 1.5% or less

10V p-p or more

5% or less at 50Hz
200ns or less
2% or less (at 1KHz, max output)
50% ±5% (at 1KHz, max output)

±1V
10V rms
Approx 10KΩ
600Ω ±10%
0dB, -10dB, -20dB, -30dB, -40dB,
and –50dB in 6 steps (accuracy:
±1dB at 600Ω load.

Within ±5%
Within ±0.5dB
0-50°(relative humidity less than
90%)
AC 100V (120V, 220V or 240V), 50­60Hz
5 Watts
See Fig. 2 on page 9
Casing 128(W) x 238(D) x
190(H)mm.
Overall (including knobs); 130(w) x

268(D) x 215(H)mm.

Weight:
Accessories:

2.9kg.
Power cord (1)
Output cord; one red and black test
cord with basket clip and antenna
plug.
Banana plug; red (1) and black (1)
Fuse; 0.125A (2) and 0.2A (2)
Instruction Manual (1)

Circuit Description

1. Summary

When reading the following descriptions, refer to the block diagram (Fig. 1) and the
schematic diagram.

The sine-wave signal generated by the Wien bridge oscillator circuit is fed through the
WAVE FORM selector switch set at the " ~ " position to the OUTPUT control, by means
of which it is adjusted to any desired voltage.

If the WAVE FORM switch is in the “ _ _ ” position, the sine-wave signal is shaped into
the square wave and the voltage is also adjusted by the OUTPUT control.

The signal voltage thus adjusted is applied to the output circuit, where its impedance is
appropriately converted, and then delivered through an output attenuator to the output
terminal. The attenuator provides selectable attenuations of 0dB through -50dB in
10dB steps at 600Ω of output impedance.

2. Wien Bridge Oscillator Circuit

The Wien bridge oscillator circuit elements consist of the resistance elements, which
may be switched over for 5 ranges by the FREQ. RANGE switch, and the variable
capacitor controlled by the FREQUENCY dial.

These elements provide means to vary the oscillating frequency continuously over 10
times its frequency on one range, thus determining any desired frequency within the
entire frequency range from 10Hz to 1MHz.

The amplifier circuit for the oscillator circuit is composed of a 2-stage differential
amplifier and an output stage, employing an DC amplifier circuit. The first stage is a
high input impedance circuit with FET while the driver stage is a wide band, high
amplification type circuit with PNP transistors featuring high cut-off frequency. The
output stage is a SEPP circuit using complementary transistors.

The output voltage is fed back with positive polarity through the oscillator elements to
form an oscillating circuit, while it is also fed back with negative polarity through the
non-linear thermistor to stabilize the amplitude.

3. Square Wave Shaping Circuit

The square wave shaping circuit is a Schmidt-trigger circuit in which the sine wave
signal from the oscillator circuit is shaped into a square wave. It is composed of an
emitter coupled Schmidt-trigger circuit and a buffer amplifier, thus providing sufficient
rising and falling characteristics.

4. Output Circuit

The output circuit converts the impedance of signal from the OUTPUT control and
feeds the signal to the output attenuator at a low impedance. It is a SEPP-OCL circuit
employing complementary transistors to provide sufficiently low output impedance
characteristics over the range from DC to 1MHz.

5. Output Attenuator

The 6-position output attenuator selects attenuations of 0dB to -50dB in 10dB steps. At
the 0dB position with the OUTPUT control turned fully clockwise, the output voltage
(sine wave at no-load time) is more than 7V rms.

The output impedance is rated for 600Ω and the attenuation accuracy is as high as
±1.0dB at a 600Ω load.

6. Power Supply
The Power supply circuit is powered by AC (100V, 120V or 220V) and delivers DC
±22V sufficiently stabilized by large capacity smoothing capacitors (220OmF x 2) and a
voltage stabilizer.

Panel Controls and Their Functions

The table below describes the functions of panel controls. Refer to the panel diagram
on page 9. (Fig 2)

FRONT PANEL

This lamp (light emitting diode) lights when POWER switch (2) is ON.

2. POWER
Pushbutton type switch turns on the power when pressed.

3. ATTENUATOR
6-position output attenuator selects attenuations of 0dB to -50dB in 10dB steps.

4. OUTPUT

Output terminal used for both sine wave and square wave.
The marking indicates GND (case grounded).

5. WAVE FORM
Output waveform selector switch. When pressed to “~”, output signal is sine

wave. When pressed to “_ _ ” the signal is square wave.

6. FREQ. RANGE
Oscillating frequency range selector switch which selects the ranges in 5 steps

as follows:

X 1 10Hz -100Hz
x10 100Hz- lkHz
x100 1kHz - 10kHz
x 1K 10KHz – 100KHz
x 10K 100KHz – 1MHz

7. Amplitude

Amplitude adjuster to continuously vary the amplitude of output voltage.

8. FREQUENCY DIAL

This dial adjusts oscillating frequencies. Frequencies can be read by multiplying

the reading on the dial scale by magnification of FREQ.RANGE.

9. DIAL SCALE
This dial is calibrated with graduations of 10-100 to indicate oscillating

frequencies.

10. DIAL POINTER

This pointer indicates frequencies on the dial scale.

REAR PANEL

11. Sync.

External synchronizing signal input terminals fir GND for connection of

synchronizing signal to AG-203.

12. Fuse

Fuse fore Power supply.

13. A.C. Connector

For connection of the supplied A.C. connector.

14. Power Voltage Selector.

This selector is preset to 240V position. A.C. power of 100V, 120V or 220V

may be used by changing the position of the selector.

Operating Instructions

1. Start-up

First check that the fuse (12) and the power voltage selector (14) are in the normal
positions, then connect the supplied AC power cord to your AC outlet. Press the power
switch (2) and the pilot lamp (1) will light indicating that the unit is ready for operation.
Allow 2 or 3 minutes for the unit to warm up so that it is stabilized.