DAX60 Circuit Description
Refer to the attached schematic, KC1546, to trace the circuit descriptions
that follow.
Input and Preamplifier Circuits:
Resistor Rl and Capacitors Cl and C507
reject Radio Frequency Interference (RFI). RVl is the input LEVEL control
(potentiometer), which controls the signal level that is applied to the DAX's
preamplifier circuits. Capacitors C2 and C8 govern the low-frequency response
of the input signal,
to protect horn-type speakers. Transistor Ql is a common-
emitter amplifier that provides the preamplifier gain. It is also a common-
base invertor for the feedback entering its emitter.
Power-Amplifier Circuits: Transistor Q2 is a high-voltage-gain amplifier
that drives Transistors Q3 and Q4.
The latter are phase splitters that form a
unity-gain configuration. Diode D503 is a negative-temperature-coefficient
device mounted on the heat sink. This diode controls the DC bias for the drive
and the output transistors. Transistors Q505 and Q506 are current amplifiers
(drivers) that supply high base current to the output transistors, 4507 and
Q508.
The latter are push-pull power amplifiers that drive the output trans-
former. Capacitor C506 blocks DC from the output transformer and limits the
low-frequency output to protect horn-type speakers.
Protective Circuits: There are several protections against excessive cur-
rent. Resistors R16 and R19 are current limiters; if a short occurs across the
audio output, each resistor will drop 10 VDC. An excessive current surge will
cause the fuse to open. In the 28-VDC supply, a short circuit on the DC output
or a DC load that draws significantly more current than 1.2 Amperes will cause
Thermal Breaker CB2 to open within 70 seconds. It will try to reset within 15
seconds, then continue opening and closing until the short or the excessive
load is removed, at which time it will remain closed for normal operation. A
more serious problem will cause CBl to open;
it must be reset manually.
DAX120 Circuit Description
Refer to KC1547 (attached) to trace the circuit descriptions that follow.
Input and preamplifier circuits:
Resistor Rl and Capacitors Cl and C5O7
filter Radio Frequency Interference (RFI). RVl is the input LEVEL control (po-
tentiometer), which controls the signal that is applied to the preamplifier
circuits. Capacitors C2 and C9 govern the low-frequency response of the input
signal, to protect horn-type speakers. Transistor Ql is a common-emitter am-
plifier that provides the preamplifier gain. It is also a common-base invertor
for the feedback entering its emitter. Q2 is an emitter follower.
Power-amplifier circuits:
Transistor Q3 is a high-voltage-gain amplifier
that drives Transistors Q5 and Q6. The latter, operating as phase splitters in
a unity-gain configuration,
provide the drive for Transistors Q505 and Q506.
Q505 and Q506 are the drivers for the output transistors (Q501-Q504). Diode
D503 is a negative-temperature-coefficient device mounted on the heat sink.
This diode controls the DC bias for the driver and output transistors.
Trans-
istors Q5Ol through 4504 are push-pull power amplifiers that drive the output
transformer. Capacitor C505 blocks DC from the output transformer and limits
the low-frequency output to protect horn-type speakers.
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