Monitor Circuit - Tascam 122 Service Manual

122
I
3-12. MONITOR CIRCUIT
See Fig. 3-27.
The tape reproduce signal or sou rce signal select·
ed by MONITOR switch S2-5 is distributed to
three lines : the output circuit, phone ampli ­
fier, and meter amplifier. The output of the
meter amplifier is sent to the VU meter circuit
and peak indicator circuit.
RI27
TP. I
QI04
TAPE
SOURCE 0
S2-5
I
OUTPUT
I
R34
~I---f:() ) L
RI28
R ch
-----POWER MUTING SIGNAL
I
MONITOR
I
I
PHONES
I
R73
I
PHONES
I
INPUT
SI- I
LINE 2 0
R340 rUNE I 0
-r23V ---¥.~'t
......
....::.;..:.~
TEST
FROM
@
IN Fig. 3-25
(
L LEVEL ONLY DURING )
RECORD/REPRODUCE AND
RECORD/PAUSE MODE
R
ch
----+--t-l
R701
,
~
?--YAO
•
R ch
R718
() PEAK LEVEL
PEAK
"' , .,
R72
INDICATOR CIRCUIT
r-----+l4+-+5.3V
R714
0704 ,U701
METER
AMPL.
0702,0703
R713
C705 R712
0701
WMETER
MI
0702
R706
-3V
Fig. 3-27 Monitor circuit
3-12-1 Output circuit
The monitor signal selected by the MaN ITOR
switch is output to the OUTPUT terminal via
resistor R 127 and OUTPUT control R34.
The rated output level at the OUTPUT terminal
is -7 dB when the level at TP1 is 580 mV (Dol ­
by level). At this time the VU meter reads
+3 VU.
3-12-2 Phone amp lifier
The deck is provided with PHONES control
R73. This allows the headphone monitor level to
be varied independently of the VU meter
reading and the output leve' l at the OUTPUT
terminal. The maximum output of the phone
amplifier is 100 mW into an 8-ohm load.
3-12-3 Meter circuit
1) M.eter sensitivity switching circu it
The bias and equalization of the deck are ad­
justed for suitability with different types of
tape. I,n addition, the deck is provided with a
BIAS/REC calibration circuit that allo\(\ls bias
to be adjusted to the most suitab fe value for
the individual tape used to optimize tape per­
formance. When adjusting bias and recording
level using this circuit the signal input level
at the LINE 1 term inal is -30 dB, which is 20
dB lower than the rated input level of -10 dB.
This low level would not normally be read by
the VU meter, so a circuit which increases
meter sensitivity during adjustment is pro­
vided.
32