Peavey Triumph 60 Effects Loop noise

[abracadabra]

Hi, first post!

Here's my problem:

I'm running a Peavey Triumph 60 with three pedals in the effects loop. A Boss NS-2 (with a 9v adapter), and two 18v MXR pedals, each with their own adapter.

When both the MXR pedals are on, there is no hum or buzz, but when one or both is off, or even bypassed and unpowered, there is a really annoying buzzing/humming sound.

When I connect the Send to the Return of the effects loop with just a cable (i.e. no pedals), there is no hum or buzz.

When I use the pedals, in any combination, on or off, in FRONT of the amp, there is no hum or buzz.

On a couple of the cables, when I connect the Send to the Return line, and then touch the two ends of the cable that are plugged into the amp (i.e. the outside grip of the jack) there IS a hum or buzz, but not on other cables.

So do you think I have:

1) Bad cables
2) Incompatible pedals or power sources
3) A problem within the effects loop part of the amp.

Thanks for any help or advice.

[nashvillebill]

The effects loop on this amp merely consists of two jacks. The output from the amp's preamp section--the amp's regular preamp signal--goes to the "efx send" jack. There is a jumper that connects to the second jack, the "efx return" which is a switching jack. If you don't have anything plugged into the "efx return", the switching jack connects the jumper from the first "efx out" jack to the circuit that goes to the amp's power amp section. If you plug anything into the "efx return" jack, the jumper is interupted and the signal from the plug that's plugged into the "efx return" is what's sent over to the amp's power amp. This is a very simple, direct connection so as long as the switching jack is making contact, there's nothing to go wrong with the efx loop. You've also confirmed this by plugging a cable from the "efx send" to the "efx return" (in essence, you've duplicated the internal jumper between the two jacks).

So, to make a short story long:
-There does not seem to be anything wrong with your amp's efx loop
-Cables are always suspect, try each of them one at a time in the efx loop, going from efx send to return.
-It could be ground loop hums between the various pedals. Try running them on battery power alone.

Schematicheaven.com has the schematic for the amp but the site has been down all month. I'd post it here but it's 10 meg.

[abracadabra]

Great thanks. I was hoping you'd reply (I've read a bunch of your other posts about the Triumph 60)

I guess it's gonna be batteries then. I'll also look into some better quality cables.

[nashvillebill]

You might also try one of the Ebtech "hum eliminator" gizmos. I've never tried one so I can't vouch for their usefulness.

[Enzo]

10 MEG???? What is it, a bitmap scan?

Peavey will send any schematic you request. Here is the Triumph. It is a pdf and a lot smaller.


And I agree it sounds like a ground loop.

[nashvillebill]

Yep, the copy on my work computer is either a GIF or a BMP, so it's huge!

Note there are a couple of minor errors on the schematic. The biggest one is the location of the dropping resistor R59 on B+. The connector shown after the resistor should be before the resistor R59, so the full 508 volts is your plate voltage, and R59 drops the voltage slightly for the screens. The standby switch does indeed kill screen voltage. Also, there's a minor error around R87 or R88. And some of the heater pins are mislabelled