Belles 350a or Mccormack DNA -1 Deluxe?

+1 Mofimadness and JohnnyR, I have owned the Belles 150a and
McCormack amps, their advice nailed it.

Truly liked this thread. Much great advice given by those who know via experience. Have heard both amps, however never owned either due to budget constraints at the time.

I ended up with the Belles 350a. Sounds great, but it has introduced a thumping woofer problem when my preamp goes from standby to active mode. Not sure what the problem is.

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.

Nice amp
I would re seat the tubes in their sockets.
with the pre amp off of course
Is thumping in both channels or just one?
if just one swap rt channel line tubes with left ch tubes and if it moves replace the tube in that channel.
JohnnyR