Constrained layer damping tape on toroidal transformer?

Getting rid of DC on the AC line with a DC blocker is the best option. Even a slight amount (less than 1/2 volt) can cause many toroid transformers to become noisy. DC blockers are not expensive.

Most damping materials are also insulators. Transformers need to get rid of heat which can damage their windings. So damping materials can be risky.

Here's a little tip which might help though! The idea of a toroid transformer is less radiated magnetic field which toroids do quite well but they are not perfect. As a result, the bolt that holds the transformer in place should be a non-magnetic material such as non-magnetic stainless. A regular steel mounting bolt is often a magnetic short to the transformer and so its common for the mounting bolt to run considerably hotter than the transformer itself as a result! So replacing the bolt with a stainless bolt can reduce the load on the primary, and can help to silence the transformer.  As a further tip, **do not** use a stainless nut to secure the bolt or you will have to break the bolt to remove the nut. Use a self-locking regular steel nut.


We found this fact out about 30 years ago- but I've yet to run into a toroid transformer vendor that knows it.

Thanks for the tip, Ralph! I think I’ll mount my transformer with a non-magnetic stainless bolt.

I would like to know why you say not to use a stainless nut, though. I build a lot of stainless parts for race cars and for food and beverage and try not to use stainless nuts on stainless bolts due to galling, but that’s only if they have a decent amount of torque applied to them. For lightly tightened things like a transformer, though, there usually isn’t a galling problem. So, why not use a stainless nut? You could always use a little bit of anti-seize if you’re worried about galling.

Ironically, perhaps, mu metal, a high permeability low frequency alloy commonly used to shield/absorb magnetic fields of transformers, including toroidal transformers, contains ferrous metal. Not sure I would pay too much attn to a ferrous nut. Or ferrous bolt for that matter. Besides as I already commented, bolts on transformers is a rather dumb idea, with the exception of shipping the component, quite unnnecesasry and bad for the sound. 

Sorry, but not bolting a high voltage component to the chassis is idiotic. Plus, if you isolate the bolt and transformer correctly, it will be like it’s not bolted in at all until you actually need to count on the bolt, like if you pick the component up and forgot you didn’t bolt it in, someone bumps it, etc.

Why not leave the transformer outside of the chassis and just run the wires into it? I mean, you might as well go all the way if you’re going to be dangerous about it.

If you can’t remember eat more fish. 🐟 🐠 🐟 🐟