On Mon, 18 Aug 2008 00:45:38 -0700 (PDT), put
finger to keyboard and composed:

I guess the offset is fixed instead of adjustable. And, I'm guessing
that I'm most likely wrong but, does the idling current adjustment
have any relation to and significant effect with the DC offset?

AIUI, the two are unrelated. The offset is close to zero due to the
negative feedback of R514 which ensures that the voltages on the bases
of the differential pair (Q501) are equal.

I don't know why but, after setting the idling current to factory
specs, the amp appears to be stable; the heatsink and transistors
don't run hot and the protection never trips while playing music
through it for 4 hours straight with a pair of Yamaha S55 monitors.
It never worked that well until after the adjustment was done.

And, when setting R607 to where the test lead shows 7.5mV on R ch. and
doing the same for R507 for L ch., the resistance reading were, more
or less, ended up being the same on both pots.

But, when I set R607 to a setting that ends up reading 100mV at the
test point, the heatsink gets kind of toasty and the protection kicks
in within a few minutes.

By my reckoning, 100mV would result in an idle current of 0.4 amp
which would in turn result in a dissipation of 32W.

Anyway, congratulations on getting your amp working.

- Franc Zabkar
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