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5. Excessive Second harmonic distortion in output
Refer to Figure B above and note the character of second harmonic distortion. This is
caused by an imbalance in amplifying capability in either the current amplifier or the voltage
amplifier. Note that the "Distortion Waveform" could also be inverted in relation to above
depending on the polarity of the imbalance. Place a probe on the output of the amp and
adjust for around 40V P/P if the condition of the board allows this much voltage. Visually
note the characteristics of the waveform and then probe on both sides of C12. C12 is
across the input to the current amp. If the waveform visibly appears almost identical (Same
P/P voltage, same waveform shape) then the problem lies in the voltage amp. Proceed to
"Voltage Amp Test". If there is much difference between the output waveform and the
waveforms measured at C12 there is probably a problem in the current amp.
6. Bias Reference Test
The purpose of the bias reference circuit is to provide bias to the driver and output transis-
tors to just barely turn them on. Q6 is a positive current source and Q8 a negative current
source. The voltage between the collectors of Q6 and Q8 is regulated by the bias reference.
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