Star Tech Journal

S*TJ DECEMBER 1981 5
regulator stays quite constant over
wide temperature variations. The
short circuit current is less than
lOOma.
The -5V, + 12V and-12V
regulators utilize three-terminal
I.C.'s. These are 320T-5, 340T-12
and 320T-12 respectively.
Capacitors C31, Cl 9, C24, Cl8, C26,
and C23 bypass high frequencies so
that these regulators won't oscillate.
gain of Q2 is determined by its
emitter current, R7, and the
impedance looking into QI, the
second stage of voltage gain. Resistor
R8 provides local negative feedback
in the emitter of QI for increased
open loop linearity while C9 and QI 's
voltage gain provide a dominant pole
open loop roll-off to ensure stability
of the amplifier. Diodes 04 and 05
provide a small amount of turn on
bias for the TIPI20 and TIPI25
darlington current amplifiers.
Resistor R22 is bootstrapped by
CIO to make R22 look like a
current source. This technique allows
maximum negative voltage swing for
a symmetrical output waveform at
full power. Local feedback in the
output stage is provided by R 14 and
R15. The overall voltage gain of the
amplifier is set by the ratio of R9 and
RIO. The actual value is
AUDIO AMPLIFIER
CIRCUIT DESCRIPTION
The G-80 power supply has
provisions for two audio power
amplifiers. The input signal from
the volume control is coupled to
differential pair Q2 and Q3 via C5 .
Resistor R5 sets the input impedance
at 22K ohms. Resistor R6 sets a
current of approximately 2 ma for Q2
and Q3 to divide equally. The voltage
R9 + I = --
22K
+ 1 =
-
RIO
IK
--
23 or 27db
Capacitor C7 .idd \ additional high
frequency compensation and the
C8 - RIO combination determines
the low frequency roll off point of
-3dbat 16Hz. The CI I -RI7
combination provides feedback loop
stability in the event that a speaker
is not connected. The maximum
output is approximately 25 watts
into 4 ohms and 15 watts into 8 ohms.
ADJUSTMENTS
I. Adjust R3 I for 5 .0V at the
load. This compensates for
wiring losses.
2. There are no other adjustments.
The tolerances are as follows:
-5V + 0.2V
+ 12V +0.5V
-12V + 0.5V
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NOTE : AL L RES!':-TANCE.
VALUES ARE IN OH MS, 112 W .! S"/., .
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COURTESY OF SEGA/GREMLI N"S TEC HN ICAL N EWSLETTER ·DATA BUS ..
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