Akai GX-636

a=| WAVEFORM SHAPING
1-2. CIRCUIT FOR PREVENTING CLICK NOISE
DURING TIMER RECORDING
1) When the power is turned on for timer recording,
recording must take place after the amplifier
circuit is in full operation or else click noise will be
recorded. Also when the power is turned off, Rec
Final Mute must operate before the amplifier
circuit ceases to operate or else click noise will be
recorded. This circuit prevents such click noise
from being recorded.
2) In ordinary recording, base electric current flows
to-TR28 base through R89 and R90, and TR28 is
ON. Therefore, Rec Final Mute relay RL1 (Pre
Amp P.C Board) connected to TR28 collector is
operating to supply the signals to the recording
head and the recording mode is effected.
3) When the power is turned ON at timer recording
stand-by, base electric current is supplied to TR27
base only while C42 is being charged and TR27 is
turned ON. When TR27 is turned ON, electric
potential is not supplied to TR28 base and TR28
is turned off. Consequently relay RL1 does not
operate and Rec head is not supplied with a signal.
Since TR27 turns off once C42 is charged, base
electric current flows to TR28 base through R89
and R90.
Because relay RL1 function only after the ampli-
fier circuit is in complete operation, the click noise
is avoided.
4) TR20 and TR21 is OFF during recording mode
and for this reason C32 and C33 are charged.
When the power is turned off in this condition, by
the charging voltage on C33 TR20 base will
become lower than the emitter in electric potential
and turns ON. TR21 is also supplied with electric
current thereby and is turned on. When TR21 is
turned on, C32 is discharged, and IC1 terminal 2
(Stop) becomes ground potential through D24.
This releases the deck from the recording mode
and the stop mode is effected.
This operation takes place before the amplifier
circuit stops and therefore the click noise is cut
out.
5 VELOCITY —™ PULSE WIDTH CONVERSION
STANDARD VOLTAGE
DC POWER AMP
SAMPLE & HOLD
STANDARD PULSE
Fig.5 Block Diagram
2. THE SAMPLE AND HOLD SYSTEM
SERVO MOTOR (SCM-200) OPERATION
1) Servo signals generally created proportionately to
the number of revolutions of the motor are shown
either as frequency deviations or voltage deflec-
tions. The motor employed in GX-635D uses
frequency deviation unaffected by time constants,
etc., of the load circuit as input signal to the
motor drive circuit through pulse width conver-
sion.
This pulse width varies proportionately to the
deviations in the number of motor rotations. The
deviation is detected, converted to a voltage value,
is held at that voltage until the next servo signal
pulse, and then impressed into the motor drive
circuit.
Meanwhile, since it requires a holding circuit and
because 112 pulse are generated for each motor
rotation, time constants of circuits coming before
the Sample and Hold circuit can be greatly
reduced compared to the conventional voltage
deflection detection system.
For the reasons above, it features quick response
to motor revolutions, minimum influence by tem-
perature, and fewer chances of faulty mechanism.
In addition, due to the inclusion of the servo .
voltage holding circuit, ripple content of the servo
voltage holding circuit, ripple content of the servo
voltage has been sharply reduced to result ina
smooth and stable tape transport with a minimum
of wow & flutter.
en
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