A and T Labs K6, Инструкция по сборке

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A and T Labs K6 Audio Power Amplifier Assembly Manual
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2001 A and T Labs Inc. AMK6a
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2.2 INVERTER POWER SUPPLY
Figure 3 shows the power supply schematic. The inverter power supply is a basic off-
line full bridge design, with output current protection and shutdown capability, and three
output voltage setting options.
The power line input is filtered and rectified by L3, DB1, and C1/C2. With JMP1 in
place, DB1, C1 and C2 form a voltage doubler. Q1-Q4 constitute the bridge, with
Q1/Q2 and Q3/Q4 conducting alternately in pairs. They are driven via pulse
transformer T2 from pulse width modulator/driver IC1. T4 is the main power
transformer, driven by Q1-4, with its output rectified by fast recovery rectifiers D1-D4
and filtered by C17-C20. The positive output is divided by R26 and R27. R27 is in
parallel with R32, R33, or nothing. The feedback signal is fed to inverting buffer
amplifier IC3a, whose output is summed with a similar divider fed from the negative
supply rail. IC3b is an inverting summer whose gain of .42 is set by R37/R36. Diodes
D12 and D14 ensure that neither power rail supplies more than approximately half of
the 11.9 volt summed input necessary to generate the +5 volt sum output. The result, at
pin 7 of IC3 is fed back to the pulse width modulator comparator input pin 2 of IC1,
where it is compared with the internal voltage reference applied to pin 1. The feedback
path includes a compensation network consisting of IC2b, R25, C24, C25, and R39.
Current in the bridge inverter is sensed by current transformer T3, whose output is
rectified and filtered by D5-8 and C22. T3 puts out 2 volts for every amp of current. The
result is compared to a fixed 2.5 volt reference by IC2a, and if excessive currents are
detected, a shutdown signal is sent to IC1 pin 10, and LED1 lights. The shutdown
condition is latched via the D11 feedback path, until C26 charges, at which point Q5
will reset the shutdown condition.
To power the inverter control circuits, a small low voltage supply consisting of T1,
rectifier DB2, and regulator REG1 gen 12 volts. Power for the fans, when used,
is generated by a separate winding on T4, rectified by D15 and regulated by REG2.
3. CONSTRUCTION
The amplifier was designed to minimize the need for point-to-point wiring by including
many interconnect features on the printed circuit. Several features, such as bridging
capability, are also optional. Variable board populations associated with these will be
pointed out during construction. The options are summarized in the following table: