Peavey Heritage Voice Coil rubbing sound

[cejay825]

Picked up this amp a while back and got it working (thanks to Enzo). V3 tube had a melt down and cause alot of problems. Got everything back to working and sounds great BUT I have noticed lately, when playing a bass heavy note ( F, F#, G etc) after the note begins to taper off and die down, it makes a sound as if the seaker voice coils are rubbing......kinda like a blown speaker or a very subtle distortion. It ONLY does this on the clean channel.....it does not do this on the distortion channel. While its being played ( on both channels), its fine and sounds good....but on the clean channel when the sound dies down, you hear the speaker rubbing sound. Just trying to find out where I should start looking first.

[Enzo]

You should verify that regardless of what we might THINK, that it is or is not the speaker. Play the amp through different speakers to see.


And try plugging the guitar into the power amp IN jack, that should be strong and clean, is it?


If it truly is a preamp problem, then I start by looking for unwanted DC offsets in the signal path.

[Jazz P Bass]

You will have to try another speaker.
If it is coil rub, you can check that maybe the spider glue broke loose.
Reglue it if it did.
Anything else would require a complete reconning.

[cejay825]

I have tried different speakers with the same result..... I'll try pluging the guitar into the power amp jack and get back with what happens.

[Jazz P Bass]

It;s the Heritage VTX, correct?
Turn off the Reverb.

[cejay825]

It;s the Heritage VTX, correct?
Turn off the Reverb.

Ok, I'll try that too

[cejay825]

Ok, its in the pre amp section. Took another amp and ran it into the peaveys power amp in and its not there....like wise, I pre amped out of the peavey into another amp and the sound is there. It is only in the clean channel though. Turning off the reverb didnt help. One thing of note, dont know if this has anything to do with it but C74 gets kinda hot to the touch. Check the picture....im I crazy or is this labeled wrong ?

Forgot: Plug the guitar straight into the power amp in ( or out, as the amp says) and the sound isn't there.

[Jazz P Bass]

That rear panel is labeled incorrectly.
The Clean channel is separate from the Lead channel, control wise.
So see if any Clean controls will change the noise. (for better or worse)
And the Phaser should be off.

[cejay825]

None of the controls really matter...... the sound is easier to hear with the Post knob high and the Pre knob low...but no matter how you adjust them, its stilll there. I did notice that C75 is also hot, like C74....don't know whats going on there but replacing the zeners in that area (CR50 & 51) is what made the amp start working again originally. I did swap the clean and distortion channels op amps....no change.

[Enzo]

In the clean channel I see about five little 2.2uf 35v electrolytic caps. This amp is 30 years old, I'd replace those caps. I suspect your dirt channel needs that too, but you just can't tell because it is not a clean channel. I see six op amp stages, check all of their output pins for DC offset.

[cejay825]

Can't find any polarized 2.2uf....found plenty of no polarized...will they work? Also, how's the best way to measure dc off set, which op amp pins and the amp on or stand by, speaker load or not ??? Thanks

[cejay825]

ok, I see the outputs on the schematic...but don't know what state the amp needs to be in when getting readings....

[Enzo]

http://www.mouser.com/ProductDetail/...WYnIe76rAz0%3d

There is one example of a suitable cap, there were a number of others.

Non-polars would work, but the right parts are available.

You are trying to take measurements of voltage and stuff, so the circuit must be live and ready to play. This is a tube power amp and so MUST have a load on the output when powered and on.


Op amps have output pins, you look at each output pin and see if there is some DC voltage there instead of zero volts DC.

[cejay825]

Thanks for the link....I'll order and get back