Woofer thump when preamp comes out of standby

This does not indicate a problem with either the amp or preamp. It is generally recommended to power up a system from source electronics to power amp (power amp on last.) When you power down you do the reverse, by turning the power amp off first and then the preamp. This avoids any transients from the power up sequence of the preamp being sent to the power amp. You should wait until the preamp comes out of its mute or standby state if it has one before powering up the amp.

Bill_k is correct. There's nothing wrong with your amp. My Rowland does the same thing, as do many other amps.

I just posted this on the other thread:

I'm assuming you are talking about the auto-warm up
feature on the PV7 that stays muted for about 45-60
seconds after turn on?

Your PV7 inverts phase through the line stage, but not
the phono stage.

Did you swap the positive and negative at the amp OR at
the speaker? Do just ONE swap, not both. That
"might" solve the problem.

Did your old amp do the same thing?

You should always turn the preamp on first, then the amp.
You reverse this sequence when you turn off the gear.

You might wait until your preamp has gone through the
auto warm-up sequence, THEN turn your amp on. That
will keep this from happening for now. There should be a
capacitor or resistor in the PV7 that should keep this
from happening. Maybe call or email cj and see what they
say. You could also call David (Belles) and ask him. He's
a pretty cool guy and would most likely know.

It could also be that the interconnect cable isn't shielded,
(at all or not properly). I've had this happen a few times.

I put my cary tube amps back in the system and the problem is there. I have tracked it down to the preamp. I tried changing tubes with some extras I had, no help. With the cover off and a power line glove on, I moved the line stage tubes just a bit and the hum changed with every tiny move. I swapped a SS preamp into the system and the problem isn't there so I am going with a problem with the preamp. I tried switching the speaker wires as indicated and that didn't work. I also tried as suggested to power up the source and allow the preamp to come out of standby before powering up the amp and the problem is still there. The only time the problem goes away is when intake the CJ PV-7 out of the system completely. I guess I'll send it back to CJ to have them troubleshoot it. Could it be just a bad tube socket? The preamp IS 30+ years old.
Thanks for all the help