Do all toroidal transformers hum?

How did you get from "can't hear any hum more than four inches away"... to.... "All toroids are inferior?".

If you aren't wearing the amps as headphones the hum issue should pose no significant issues.

Certainly, if you have toroids in your amps and don't like your amps... perhaps only those toroids in your own amps are inferior.

Relax. Don't sweat the petty stuff, but do remember to pet the sweaty stuff now and then.

Stan outlined it pretty well already.

The reason for the hum is what is called magnetostriction. You can read about it here.

It may also be sensitive to the tightness of the transformer mounting screws, and to the design of the mounting arrangement, which might influence the degree to which the vibrations are amplified or damped by the surrounding structure.

Regards,
-- Al

Almarg, don't forget dc in the line and poor construction.

You may also help by using either coupling or isolating devices under your amp. Although they work on opposing principals I have found both to improve the sound to a surprising degree. I have been using Audio Points from Star Sound but am now using FIM isolation devices [modified] under all components. But there are many others.