Echo Rcv Circuit; Meter Calibration And Led Circuit; 5.18 Test Tone Oscillator - Teac Tascam Series Instruction Manual

5.16 ECHO RCV CIRCUIT
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1. The ECHO RCV jack is provided on the rear panel of Lo.
each BUSS MASTER Module. As the ECHO RCV
input impedance is 20kohms, the signal from an
Echo Machine can be fed to ECHO RCV jacks of
more than two channels, depending on the Echo
Machine load impedance, by connecting the ECHO
FLB with the ECHO RCV jack of another channel.
2. Apply a -10dB (0.3V) signal to the ECHO RCV jack
of BUSS MASTER Module 1.
3. Set the ECHO RCV pot fully CW.
4, Set the controls of the BUSS MASTER Module as
fotlows:
TRIM : CW to the CAL. position
FADER To "O" on scale
a . The circuit is in good condition if the output level of
LINE OUT 1 is -10dB (0.3V).
Note: Be sure the Level Selector Switch ($1}, on the
PCB of the AUX A Module, is set to LO
(-10 dB) side.
6, Check the ECHO RCV circuits of the other BUSS
MASTER Modules by the sarne procedure.
a .17 METER CALIBRATION AND
THE LED CIRCUIT
. The adjusting points in the PCB of the M-15 are, the
Overload LED Igniting Level Adjusting Pot in the
Model 301 Input Module; four Meter Calibrating Pots
and four Meter LED Igniting Level. Adjusting Pots in
the Model 303A' AUX A Module; four Meter Cali-
brating Pots and four Meter LED 'gniting Level
Adjusting Pots in the Model 3038 AUX 8 Module.
2. The circuits are identical between Model 303A and
303B.
3: The controls are set so that the LINE OUT 1 output
level will be -10 dB (0.3V).
Note: During this procedure, be sure the Level
Selector in the Model 303A AUX A Module
and Model 3038 AUX B Module PCB's are at
23
4. Under this condition, adjust R202 in the Model 303A
AUX A Module PCB so that the extreme left VU
meter reads 0 VU.
5. From the condition of !tem 3, above, raise the out-
put level 10dB for OdB (1 volt) output. Then, adjust
R201 so that the LED inside the extreme left VU
meter lights-up.
6. As U5-1 has a gain of 11.8dB, when a OdB (1V)
input signal which is 10dB above the LED igniting
level, is applied to pin #3 of U5-1 there will be a
+11.8dB output from pin #1. This output is then
divided by R32 and R33, the cathode voltage of D1
will be -2dB (0.8V), the signal rectified and a 1V
OC applied to pin #2 of U7-1, Adjust R201 so that
the voltage of U7-1 pin #3 will be 1 volt DC, When
the voltage of pin #2 goes higher than pin #3, the
output voltage of U7-1 will be-16 V and as the anode
of D2 will be OV, the base current of Q1 will flow to
R38 via D3 to switch ON Q1. and the LED will
Jight-up.
7. The remaining R203 through R208 are adjusted in
the same way. Adjusting procedures for R201 through
R208 in the Model 303B are also the same.
5.18 TEST TONE OSCILLATOR
i. The Test Tone Oscillator has a 3-position (TEST/
OFF/SLATE) selector switch, At TEST,.a -10 dB
signal is obtained at the OSC OUT jack on the Model
304 Talkback Module rear panei; at OFF there will
be no signal, and at SLATE, in addition to an output
signal at OSC OUT, a test tone will also be applied to
the Summing Amplifier U1-2 of the BUSS MASTER
Module via the SLATE switch on the Talkback
Module.
2. The oscillator has 6 frequencies of test tones'and the
frequency of each is determined by f = 1/2aCR.
The conditions in this circuit are, C = C7 =C8= C9,