Re: Marshall Valvestate AVT-150H hum

RichL wrote:
Elvis Kabong <ampscience@xxxxxxxxxxxx> wrote:
"Tone" <tonyc329@xxxxxxxxx> wrote in message
news:NqednfCoEcWzzUnanZ2dnUVZ_tijnZ2d@xxxxxxxxxxxxxxxx
I have a Marshall AVT-150H head that has a very noisy hum in the
Overdrive 1 and 2 channels. I only use this amp for practice, so it
isn't something I've really concerned myself with, and therefore I
can't recall if it is always been like this or it is something that
developed over time. Anyway, when I'm in the OD1 or OD2 channels,
it's noisy as hell and a tad bit annoying.

Has anyone heard of this problem and is it something correctable?
If not I can live with it, but if anyone has heard of this problem
and knows of a fix, please share.

Thanks.
One thing you could check (and this is a long shot) but it's
easy enough for you to try. If the amp has an effects loop
and you don't normally use it, there's a possibility that the
sleeve terminal in the return jack may not be making good
contact with ground when not in use. Get some contact cleaner
and spray it into the return jack and plug a 1/4' in there and
give it the ol' in-out in-out a few times or just do that without
the spray. Otherwise it's either a bad ground connection somewhere
in the amp or a leaky small signal transistor in the preamp.

Good luck,

KBG

You could jumper the loop first to see what that does. Connect a patch
cord between loop send and return. If the hum goes away when you do
that, you've isolated the problem, in which case Ed's fix might work.
If the hum goes away but using the contact cleaner doesn't fix the
problem, you're replacing a jack worst case.


Sorry, but what does the fx jacks have to do with the hum on the OD channels.
The clean channel is OK according to the OP!
As said before; check IC 8 and 10 with and without the volume pot set to min and max.
Feedback the results OP.
Zilog
.

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