> Question: Are you sure of the following things?
>
> - There really is no hum when the noise-cancelling
> feature is deactivated?

In a quiet environment the hum definitely goes away when the NC circuit is switched off and they are attached to the empeg at a paused state (or quiet passage).

> - The headphones do not produce the same hum when
> used with other pieces of consumer stereo gear?

I have connected them to my Rio 500 player, which runs off a AA battery, and I hear no hum with NC active.

...Mark