[monaro0162]

It does seem to have a problem with mains hum. I listened to it again through different amps, but I am hearing more or less the same mains hum in the background with each amp, and more hum on one channel. Its not that loud, but is loud enough to be noticeable in the background whilst playing music.

So I connected the output directly to a PC audio card running audacity and made a recording - definitely seeing more hum on one channel. If I swap the L&R line out leads from the GXC, into the audio card on the PC, the fault reverses on the audacity display, so the problem looks to be coming from the GXC. Attached is a screen shot of the Audacity analysis. The gain has been turned up to capture the hum, and more hum can be seen on one channel compared to the other.

I'm wondering if this is just a ground earth loop problem, rather than a failing power supply? I haven't actually scoped the power supply yet, I'll will try later on in the week.