Terrible buzz, goes away when i sqeeze the OT ?

[Iplayloud]

I have a Carvin 4xEL84 on the bench, it has a terrible buzz on bass notes above 3. If i compress the OT it stops. Is it possible that the laminations be loose, or that an intermittent internal short touching during vibration may be the issue ?

[soundguruman]

Terrible buzz could be the bias voltage too high, causing crossover distortion. The parts used in these amps are not remarkable for quality, and I would not be surprised if the winding was shorting to the case or core.

[Jazz P Bass]

It could very well be loose laminations.
The bass notes may be in just the right frequency range to make them vibrate.

[J M Fahey]

It's clearly "mechanical", not "electronic".
If at all possible, I would pull that transformer and submerge it for a full night in a can of transformer varnish, if available, or plain old good regular varnish, if not, followed from a couple hours hanging and dripping the excess.
If *too* thick, add a little turpentine or similar "oily" solvent, *not* car paint type thinner which is too active (contains acetone or ethyl acetate) and may eat insulation.
You can tie its wires to a stick so it stays a few inches above the can.
Then let it dry 24 hours, so it's tack free plus you let the internal parts reasonably dry too.
After remounting, it might ooze a little when it warms up, it's normal.
I very much doubt it will ever dare to buzz again.

[jrfrond]

Sounds like loose laminations to me. You could probably fix THAT issue by doping the laminations by using good ol' GC Radio/TV Service Cement, thinned with a bit of lacquer thinner. This stuff is really nothing more than nitrocellulose lacquer, so nitro lacquer and clear nail polish, both thinned to allow interlamination flow, will work also.

The underlying issue is that space between laminations reduces power handling capability. Might not be an issue in a 30W amp, but I couldn't say for sure.

[Iplayloud]

Can i dip it in water based latex wall paint ? The buzz sounds like a short that oscillates at the played frequency. The sound of the amp even changes when i press on the ot, it takes about 20 pounds of pressure.

[soundguruman]

Hose clamps, pipe clamps. Oh come on.

[Chuck H]

The sound of the amp even changes when i press on the ot, it takes about 20 pounds of pressure.

If this is true you should replace it... Oh, and stop touching it while the amp is powered up.

[J M Fahey]

Sorry, no water based *anything* inside a transformer.
Only non conductive stuff.
In the old days they potted in tar (real messy) , and even in wax/paraffin if it worked cold (as in mic or line transformers), not recommended for Power or OT transformers, though.

[soundguruman]

I think I might have gathered that transformers, hooked up to 450 volts, cannot be pre-soaked. Perhaps a person who thought that they could be pre-soaked should not be working on transformers.

But as it has been said so wisely, at this time, install a new transformer. You don't want to glue, clamp, soak, a thing that is hooked to 450 volts. It's not logical.

[Gtr_tech]

Hmmm......I bet they used a plastic bobbin. The bobbin was off spec for internal diameter so it can thrash around while trying to do its job. I'd just replace it with a better xfmr. Carvin ain't known for using top shelf parts....

You may be able to pull the end bells off and stick some wood/plastic shims in there to hold the bobbin in place. But, if the amp does not belong to you, replace it. Keep the old one to play around with...

[Enzo]

Sometimes loose laminations can be helped by torquing up the bolts.

A lot of transformers have that copper band around them, does yours? I have had those buzz, and cured it with shimming material.


It is very difficult to squeeze the transformer without at the same time causing some flex to the chassis. SO make sure all the chassis hardware is snug.

[Chuck H]

On the same point Enzo is making...

You mention that applying pressure to the OT alters the tone of the amp. It may be that there are physical problems with circuit contact that are being corrected when you apply pressure to the OT. Try applying pressure to the chassis near the OT. Do you get the same affect? I've never heard of applying pressure to the OT changing the tone of an amp before. You might simply be changing the aspect of your listening angle because of your physical position? Since your experiencing effects from squeezing ANY transformer on the amp I'm inclined to think there may be some obcessive placebo effect.?.

[Ronsonic]

Tighten everything, of course.

This is controversial, but often works when nothing else does - take a hammer in hand and dent the endbells. Just one good ding. The round end of a ball peen is preferred.

Honest. It works.

[soundguruman]

Put down the hammer, and step away from the test bench---
For your own safety.