Thanks for your comments.

The speakers are DIY and work on another amp. I think I would hear the
output click even with no speakers attached and I don't.

I wonder if it could be the 12V/signal trigger (set to bypass since I
don't have the preamp)

How do I find a circuit diagram for a rotel RB-1050?

Thanks,
Dave



p.s. The last setup with the amp was computer soundcard speaker out to
a 25Kohm stepped attenuator (another DIY) that I just finished, and a
set of crappy speakers that I could blow and not care about. Resistance
values on the attenuator checked out.
RB-1050 input overload is 1V/33kOhm, I think soundcard output is up to
~1V