Brian Powell Audio

Toroidal Transformer Mechanical Noise

Toroidal power transformers are a good way to provide power supplies for power amplifiers. They make it possible to achieve below 100uV residual noise with a good PCB and correct wiring. However, this performance is spoiled if the transformer buzzes mechanically. A resilient mounting arrangement will help. But often the culprit is the mains supply itself.

The magnetising current for a toroidal transformer can be as low as 50mA with clean supply. But if there is DC on the mains, this can shoot up rapidly as the core saturates and large current spikes begin to flow. DC on the AC mains does happen and just a hundred mV out of 230V can be a problem.

There are solutions see Mains DC and Transformers (sound-au.com) This is an excellent website.

I do not advise working with mains voltage projects unless suitably qualified.