tubed preamp off and ss amp left on?

If the preamp has a mute feature, switch the preamp to mute before you shut it down. See if that helps.

Otherwise you best turn off the power amp first then shut down the preamp.

12-17-06: Warrenh
Funny, I had posted a similar question a few weeks ago, having come back to seperates after over 20 years. If the volume is down on the preamp, should it matter which you shut off first? Nowhere in my amp or preamp manual does it say to be certain to shut off first or last. I think volume down on the pre is the answer?

When the power switch is turned off a voltage transient spike may pass thru the preamp outputs thru the ics to the Amp. Result, a loud pop. This will happen even if the volume pot is all the way down.

My Sonic Frontiers line One preamp, when placed in standby before shutting down the preamp, apparently shunts the outputs of the preamp thus preventing the voltage transients. That is the reason in my earlier post I suggested trying the mute function if the preamp has one. The mute circuit in the preamp may shunt the outputs, thus, no transient spike leaving the preamp thru the ics to the amp.....

I disconnected the preamp at the amps inputs and the strangest thing happened. The left channel was silent

You have the Amp isolated from all other outside input sources. Only the 120Vac power could corrupt the amp. But as you stated the left channel was silent . Jmho that would rule out the AC as the problem.

yet the right channel had the same hum and at the same level.

Sounds like a problem in the right channel. Time to take it to the shop for repair. Did you check if the manufacture has a ask a question website?

I then plugged the interconnects back in and the hum returned to both channels.

Almost sounds like the input jacks do not share the same signal ground.

I can't see how a speaker could cause your hum unless they have powered LF drivers.

If you want to rule out 100% a speaker causing the problem, switch the right and left speaker cables at the Amp. If the hum moves to the other speaker,(still the right channel) it has to be the amp's right channel.

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