Getting rid of that transformer humming...

[JimJ]

Mike (and others), hopefully you've run into this minor, but annoying problem...

Ever had a humming transformer? Not humming through the speakers like a ground loop, but a mechanical hum resulting from DC on the power line. It's inaudible from a few feet away, but it's still there nonetheless.

I'm trying to come up with a circuit to get rid of the DC on the AC mains, but haven't found a consesus yet of a good circuit to build. Every time I find something that seems like it would work, I get people that disagree with it - not sure if they just don't know what they're talking about, but I'm certainly not going to pay the several hundred dollars for a commercial unit that maybe has $20 in parts.

Any suggestions/schematics?

Thanks in advance.

[MikeS]

Mike (and others), hopefully you've run into this minor, but annoying problem...

Ever had a humming transformer? Not humming through the speakers like a ground loop, but a mechanical hum resulting from DC on the power line. It's inaudible from a few feet away, but it's still there nonetheless.

I'm trying to come up with a circuit to get rid of the DC on the AC mains, but haven't found a consesus yet of a good circuit to build. Every time I find something that seems like it would work, I get people that disagree with it - not sure if they just don't know what they're talking about, but I'm certainly not going to pay the several hundred dollars for a commercial unit that maybe has $20 in parts.

Any suggestions/schematics?

Thanks in advance.


Is it a tube PS transformer?
Sources of mechanical hum can be loose laminations, or the transformer needing to be tightened to the chassis from getting loose and vibrating.

If that doesn't help, then there could be a chance that the varnish on the windings is starting to break down, causing mechanical vibrations between windings.
This is usually the symptom of a PS xfomer that may had been ran hard and overheated.
One sign is if you see a bunch of wax dribbled underneath the PS xformer from the paper between windings, or dribbled on other components, such as capacitors.

If it vibrates pretty good, and has lost wax, then there is a reasonable chance that when you pull the end bells off the transformer that the windings and paper will be all black and cooked looking.

If you have a variac, you can cruise up on the primary AC voltage and determine at what point the transformer starts to go into mechanical vibration.
It may rattle at 120 VAC, but maybe not at 115 VAC.
A guy could use the variac in the primary to remedy the issue, or come up with something like a isolation transformer that can step down the secondary to the voltage required for the PS transformer.

The thing I notice with all this vintage tube audio crap with regards to the stock PS transformers used, is that the transformers are always rated at 117 volts AC.
I may have a couple rated at 115 volts AC as well.

Now 3 volts not seem like a big deal on the primary side, but it is if the PS xformer is a 5, 6.1 step up on the secondary.
That 3 volts turns into 9 or 12 volts.
It seems I always have to beat down the voltage on a vintage tube amp PS. I did on that Admiral console amp.

I'm guessing that when some 117 VAC rated PS transformers are pushed to 120 VAC, that it might be just enough to push them into mechanical vibration/stress. Where it may not even bother another PS transformer of the same rating. Ratings vary from manufacturer to manufacturer, and some xformers may be a heavier build however rated the same.

My 2A3 SET amp uses a big old Gramer brand television power supply transformer, it has the copper shorting straps. (Which I really think helps with noise.) But it is rated at 117 VAC on the primary, and it does have mechanical vibration which can be heard from 2 feet or so from the amp.
I just deal with it. A retightening is in order, however.....

You can possibly loosen the bolts and end bells of the transformer and carefully re-position the laminations provided they aren't stuck together with shellac too much.
(Usually if the are stuck together real well, they should never move.)
Sometimes the re-alignment of the laminations may help.
I've never tried it, and it kinda seems like a crap shoot, but it's a option.
I was given this advice concerning the Gramer PS xformer.....

About direct current on a alternating current mains, I dunno if cleaner AC is going to matter with a PS transformer that is either getting worn out or ran higher than it's rating. If I understand correct?

Cleaner AC is always better of course, but whether it solves a mechanical vibration in a power supply x-former, I'm not sure.

I've got a older JVC solid-state integrated amp that the PS supply transformer has mechanical vibration, it's pretty much on par with the SET amp's PS xformer.
Getting tired I suppose.......some tightening and chassis isolation would probably kill most of the mechanical noise.

I know I don't know what I'm talking about.........:shock: