It's R17 on the schematic, used for bias setting.
The procedure is the following:
1) Before the first power on - set R17 to zero (shorted) position.
2) Connect the voltmeter (some 200mV scale) - one lead to the top of R37, the other lead to the bottom of R38.
3) Power on. You should see something from zero to few mV. If you see more than 200mV - better power off, something is wrong.
4) Turn R17 carefully, until you set 65mV there - this will give you around 70mA of quiescent current through the output pair.
5) As soon as the output pair on a heatsink will warm-up, the voltage you see will slip away slowly - just correct it back to 65mV - carefully, no fast moves. It will settle completely in 20-30 minutes. Then you're done.
Cheers,
Valery
Wow Thanks for Quick response, 65mV is common value or you calculate according to my amplifier layout?
I don't know the exact designer's recommendation for the quiescent current for this particular circuit, but something around 70mA (which is 65mV across the resistors in your case) is good enough for most of the output stages of this kind.
Cheers,
Valery
i order from china via agent. That picture is dummy. Mine is here below still on progress.
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