Tascam 122 - 3-12. Monitor Circuit; 3-12-1 Output Circuit; 3-12-2 Phone Amplifier; 3-12-3 Meter Circuit

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
IMONITOR I
IPHONES I
R73
IPHONES 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
•
Rch
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
B IAS/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