Two identical amps-one has more "hum"

Keith Murrow · Post by **Keith Murrow** » 6 Jun 2002 7:44 am

..[This message was edited by Keith Murrow on 26 October 2004 at 04:32 PM.]

Donny Hinson · Post by **Donny Hinson** » 6 Jun 2002 8:14 am

Mike Brown can elaborate more on this, but there's a chance that the two "identical" amps may have minor circuitry differences, due to subtle design changes. (There are sometimes different circuits/components in same style amps.) Also, the issue of filter caps in the power supply causing this is not to be overlooked, either. Normally, the first thing I would do is a scope check for A-C ripple in the B+ line, and compare the two amps that way. Caps are relatively cheap, and can be easily replaced.

Chuck McGill · Post by **Chuck McGill** » 6 Jun 2002 10:22 am

Keith
You probably know this but make sure there
are no effect processors on top of the amp
that might pick up your transformer in the
amp and does it still hum with the reverb
off.
Chuck

Mark Herrick · Post by **Mark Herrick** » 6 Jun 2002 4:55 pm

Are you using the amps together? In that case, it might be a ground loop hummmmmmm...

Keith Murrow · Post by **Keith Murrow** » 6 Jun 2002 8:37 pm

..[This message was edited by Keith Murrow on 26 October 2004 at 04:32 PM.]

Tom Ward · Post by **Tom Ward** » 7 Jun 2002 1:52 am

Keith, Mark has the right idea! If you haven't already, try a "ground-lift" line plug adapter on one or BOTH amps. Sounds like an AC polarity problem. Sometimes when we play a gig in an older building we have to put an adapter on just about all our equipment. Tom

Keith Murrow · Post by **Keith Murrow** » 7 Jun 2002 6:20 am

..[This message was edited by Keith Murrow on 26 October 2004 at 04:32 PM.]

Dennis Detweiler · Post by **Dennis Detweiler** » 7 Jun 2002 6:36 am

My first guess is the two filter caps need to be replaced. I've had this same problem arise a few times over the years.
If all else fails, send the chassis to PV and have them go through it. I did this to my 1976 session 400. It came back like new and repair cost was very reasonable.
Dennis

Mike Brown · Post by **Mike Brown** » 7 Jun 2002 11:21 am

Keith, everyone has some good suggestions here. But, if you don't have any success is locating where this hum is coming from, please feel free to contact me toll free at 1-877-732-8391. If possible, please have your steel rig setup in front of you and I'll help in locating where the problem is.

Mike Brown
Peavey Customer Services

Bill Terry · Post by **Bill Terry** » 7 Jun 2002 2:00 pm

For safety reasons, my personal preference is not to lift the ground on equipment. Lifting the ground on all but one piece of equipment often means you are relying on a flimsy little audio cable shield to ground the ungrounded gear.

Indeed... you are very wise. Sounds like you've carefully eliminated the likely causes. As Dennis mentioned, I vote for something not quite right in the power supply filtering.

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