Onkyo TA-630D

“A-630D
CIRCUIT DESCRIPTION
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1. Accurate Bias Circuit
Optimum bias current varies according to the type of tape
being employed. Too little bias current will result in
increased distortion, while too much bias current will result
in deterioration of the frequency response. For this reason,
the TA-630D has been equipped with an Accu Bias Control
(front panel) which permits optimum bias currents to be
set accurately for different tapes.
A major feature of the TA-630D is the Accu-Bias circuit
which permits optimum bias adjustments for every
individual cassette tape used, thereby ensuring recordings
of very flat frequency responses.
1. Insert a blank tape into the cassette compartment, and
set the Tape Selectors accordingly.
2. For Accu-Bias adjustments, the Dolby NR switch must
always be in the Out position.
3. When starting at the beginning of a new tape, press the
> > FF key to advance the tape by 20 ~ 30 in the
Tape Counter. (This will ensure optimum bias adjust-
ment). |
4. Press the m= Pause key, and then the @ Rec and >
Play keys to prepare the deck for recording mode.
. Press the Memory push-button (On position).
. Reset the Tape counter to 000.
. Press the Accu-Bias push-button (On position). The
Accu-indicator lamp will consequently light up.
8. Turn the Accu-Bias Adjust control to the ‘0’ (click-
stop) position.
9. Check that the meter pointers deflect across to around
the 0 VU position. Since the internal oscillator
generates alternate 400 Hz and 10 kHz (-—20 VU)
signals.
10. Release the @# @ Pause key, and record for a count
of 5 to 10.
11. Press the << Rew key. The tape will rewind back to
000 and stop automatically.
12. Press the » Play key to playback the tape.
13. Turn the Accu-Bias Adjust control around in either
direction to find the position where the meter pointers
again swing back and forth with minimum amplitude.
This adjustment will now correspond to the optimum
bias setting for that particular tape.
14. Leaving the Accu-Bias Adjust control in the adjusted
position, press the Accu-Bias push-button a second
time to disengage the Accu-Bias circuit. Now proceed
with the regular recording.
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NASW-543_-
During recording: Q611, C610 ~ C612, R631, R632 and
R634 constitute a 10 kHz CR oscillator circuit, while
Q614, C615 ~ C617, R644, R645, and R647 constitute a
400 Hz oscillator circuit. By using a non-stable multi-
vibrator, Q612 and Q613 switch the 10 kHz and 400 Hz
signals back and forth at approximately 2 second intervals
(Q613 is turned OFF when Q612 is turned ON, and vice
versa). When Q612 is turned ON, the collector voltage
drops, resulting in Q615 being cut OFF. And since Q613
has already been cut OFF, Q616 will be turned ON,
resulting in the 10 kHz signal passing out through the
ACCU OSC output. When Q613 is then turned ON, Q612
is cut OFF immediately, resulting in the 400 Hz signal
appearing at the output. These output signals (alternate
10 kHz and 400 Hz signals of equal levels) are then passed
to the recording amplifier (Q111) prior to being recorded
on tape.
During playback: The recorded signals are passed via a
playback equalizer amplifier, a preamplifier, and a line
amplifier. The 400 Hz signal is passed via the R623/C 629
low-pass filter and Q609, on to the meter drive circuit.
The 10 kHz signal, on the other hand, is passed via the
C632/R628 high-pass filter and Q610, on to the Accu Bias
Level VR (coupled to the front panel Accu Bias Control)
before being mixed in the meter drive circuit. Then
optimum bias is selected for that particular tape by adjust-
ing the Accu Bias Control to make the levels of the 400 Hz
and 10 kHz signals equal.
2. Timer Start
(1) Set the time of the timer unit plugged into the AC
mains.
(2) Press the record key and/or the play key, and also the
pause key. Then turn the power switch on.
(3) The power supply will thus come on at the preset time.
(4) C701 will consequently be changed up via R702, result-
ing in Q701 being turned ON some 4 seconds later.
(5) Q702 will therefore turn OFF.
(6) The signal will pass via S701 and C702, on to the gate
of Q704.
(7) Q704 will thus be turned ON.
(8) The charge on C707 will then be discharged through
solenoid and Q704, which is thereby activated.
(9) The pause key is releassed by this solenoid action,
resulting in the start of the recording, or playback,
mode.