I have a Rotel HiFi amplifier which I very much like the sound of. It still sounds fine through the speakers, but the transformer inside has started buzzing quite noticeably, which when standing near it is irritating.

Can anyone advise what causes it (I'm guessing magnetic vibration?) ... and how it could be made to shut up? As far as I can tell it's still perfectly fine electrically, since the amp works perfectly and all the voltages measure as I would expect them.

 

You need to go inside the amp and carefully with the power on do some "mechanical" adjustment to the transformer, such as try tightening or loosening the mounting bolts, adding shims or pads such as rubber or felt. It's all experimental, you need to try different things and see what works.

 

Agreed. An irritable transformer can be the most frustrating thing in the world.

Often enough, you decide you'll have to replace it...until you see the price.

Then you decide that if you can only hear it hum when the volume is turned all the way down, you can just not play it with the volume turned all the way down.

 

Or take the transformer out, suspend it in a can of varnish overnight, remove from varnish, allow to dry a week or so and reinstall.

 

Or take the transformer out, suspend it in a can of varnish overnight, remove from varnish, allow to dry a week or so and reinstall.

Does that actually work? I do actually have a tin of Ronseal Clear Exterior Varnish...

 

You need to go inside the amp and carefully with the power on do some "mechanical" adjustment to the transformer, such as try tightening or loosening the mounting bolts, adding shims or pads such as rubber or felt. It's all experimental, you need to try different things and see what works.

Are we talking the actual transformer itself, or just the way it's mounted to the PCB and chassis? I can't actually see anything to adjust... do I need to start removing the protective tape from around the coils, or is it more likely there's nothing to adjust on this one?

 

Do not try to take the transformer apart! Do not damage the tape. Do not unwind the wires.

Find a way to tighten or loosen the way it's mounted, but do not try to enter the transformer.

 

Are we talking the actual transformer itself, or just the way it's mounted to the PCB and chassis? I can't actually see anything to adjust... do I need to start removing the protective tape from around the coils, or is it more likely there's nothing to adjust on this one?

The plates of a transformer are coated with very thin layers of varnish, magnesium oxide or various other insulators to prevent eddy currents. If there is any rust or other stress on the plates, the plates will squeak/rub as they expand/contract from magnetostriction.

You can try to mechanically tighten any bolts on the transformer frame, or dip in a thinned varnish. You want it as thin as possible so it flows into any/every gap. Let it really dry. Set it in the sun on a hot day. Hopefully it will dampen the squeaks and buzz.

 

The, "right" way is to make a vacuum in the chamber with the transformers and then add the varnish. No air means no bubbles. Unfortunately, that is beyond the practical ability of most people. Just soak it, drain it, and let it dry. That's the best you can do without destroying the entire thing.

 

use the force Luke, use the force....

sorries, meant to type tighten the transformer bolts, there should be something squeezing the iron plates together