Has anyone else experienced an EXTREME amount of noise when adjusting
the gain pot on a Marquette Audio Labs V72 package? We own two of these
modules and they both suffer from this same problem. I strongly believe
that ALL of these packages probably suffer the same defect.

They achieve adjustable (and additional) gain by placing a 1,000 ohm
pot from the cathode to ground of the first EF 804s tube, and then
returning the negative feedback from the following EF804s tube via the
wiper of the pot. What you hear when adjusting the gain is a very loud,
scratchy sound that could easily blow your woofers out of their baskets!
Some LF thump, but also an unbelievable amount of unwelcome midrange
energy.

FWIW, I have looked to see if there was a large amount of DC present on
the wiper, and this doesn't seem to be the case. I even tried
capacitively coupling the wiper to the FB source to eliminate the small
amount of DC and it really didn't seem to make much, if any difference.
Neither did exchanging the pot for a better one with a conductive
plastic element. I'm stumped at this point...

I tried calling and talking to D. Marquette @ MAL and he couldn't have
been more defensive or uncooperative in resolving the problem. Go
figure. Any suggestions, or anecdotes regarding similar experience with
this issue would be greatly appreciated.

Cheers,

kerry