Sony TA-2000F - Page 9

Stage/Control
OUTPUT LEVEL
switch S13
Function
The output voltage can be
changed by Sil, which has
two calibrated positions (0.3V
and 1.0V), and should be set
according to the requirements
of the equipment to be con-
nected. Note that the signal
supplied to the OUTPUT-2 ter-
minal is routed through the leaf
switch in the HEADPHONE
jack. As the result, no signal
will appear at the OUTPUT-2
terminal during headphone mon-
itoring.
Meter
Amplifier/Headphone
Amplifier
Section
METER LEVEL
switch S12
Meter amplifier
Q701, Q702
Q703
Level meter
adj. R701
Headphone
amplifier
Q704, Q705
Q706, Q707
HEADPHONE
LEVEL VR9
Level meter sensitivity can be
varied by switching S12. In
OdB position, the reading on
the meter shows the actual out-
put value. In the -10 (-20)dB
position, the sensitivity of the
meter increases 10 (20)dB up
from the 0dB position. Output
signal is routed to meter ampli-
fier through METER LEVEL
switch $12 to permit VU meter
monitoring. In the MIC posi-
tion, only the MIC amplifier’s
output is fed directly to the
meter amplifier.
This three-stage direct-coupled
amplifier increases the extracted
output signals to the level re-
quired to drive the level meter.
The meter amplifier output is
rectified and supplied to the VU
meter through bridge rectifier
diodes D701 ~ D704.
Semifixed resistor R701 in the
meter amplifier calibrates the
VU meter.
Supplies enough power to drive
the headphone used for mon-
itoring. The output signal is
controlied by means of HEAD-
PHONE LEVEL control VR9.
Q704 is a preamplifier which
increases the input signal to the
level required at the following
driver stage.
Stage/Control
Driver Q705
Power amplifiers
(complementary
stage)
Q706, Q707
CENTER
CHANNEL
OUTPUT jack
Muting circuit
Q907, Q908
Q909, Q910
19 ey Lelele) :
Function
Though this stage is a conven-
tional flat amplifier, it deter-
mines the output voltage swings
because the following stage is
basically in the emitter-follower
configuration. The ac load resis-
tor for this stage is R718 in the
coHector circuit.
These transistors operate as
emitter-followers to provide the
current swings required and also
perform the necessary phase in-
version to drive the load in
push-pull.
Phase inversion is performed by
using PNP and NPN type transis-
tors. Q706 supplies power dur-
ing the positive-going half cycle,
while Q707 supplies power dur-
ing the negative-going half cycle.
The output is fed to the HEAD-
PHONE jack through coupling
capacitor C711.
It also supplied to the CENTER
CHANNEL output jack through
R729 for use in center-woofer
systems. Note that the left- and
right-channel signals are mixed
at this jack.
This muting circuit prevents the
loud ‘‘pop” (due to initial cur-
rent flow) or click noises from
occurring just after turning the
power switch to ON. These
transients might damage a deli-
cate high-fidelity speaker system.
The base of Q909 (Q910) is
connected to the collector cir-
cuit of Q908 through R914
(R913), while the base of Q908
is connected to an RC network
(R910, C902) having a long
time constant. Negative bias
voltage is produced by D907
and C903, and then fed to the
base circuit of Q909 (Q910)
through R912. This effectively
mutes the input signals up to
20V_ peak-to-peak. When you
first turn ON the power switch,
Q908 remains off due to the
long time constant of the as-