I ran across this post accidentally, just now (I'm the moderator from the 'Ask a Guitar Tech' forum)...

Mikey54, if I understand your initial posting correctly, it doesn't sound like there's anything wrong with your amp, at all. Having any amp make a lot of 'buzz' when set on a high-gain channel with a cable plugged in, [u]but no guitar connected to the other end of that cable[/u], is [u]completely normal.[/u] Plugging a cable into an amp, without a guitar connected to the other end of the cable, doesn't tell you anything useful - the 'open' cable itself will generate quite a lot of 'buzz' itself. All modern amps have a 'shorting' input-jack, that connects 'hot' to 'ground' within the input-jack itself, when no cable is plugged into the input-jack. This is done specifically to prevent the problem you're experiencing.

The testing you performed (which you described very accurately, btw) does not indicate a faulty cable (at least, not to me) - instead, it indicates that your amp is working normally. If your guitar is built with single-coil pickups (e.g. a Stratocaster or Telecaster, or a guitar with Gibson 'P-90' pickups), the single-coil pickups will induct a lot of 60Hz hum ('buzz') from the outside world, and this hum is being amplified greatly by the high-gain setting in your amp.

I guess that your amp (which is fairly basic) doen't have any elaborate shielding for its circuitry, so it may be more sensitive to outside 60Hz noise than some more-expensive amps, and/or that the amp's high-gain setting (which is a digital emulation of an analog 'tube' cicuit) may, for whatever reason, just be more sensitive to this noise than an 'analog' circuit usually is...

In any case, I have no reason to think that the culprit is your cable. However (fyi), there are 'directional' cables taht are specifically engineered to reduce 60Hz noise from single-coil pickups. These cables are quite specialized (read: expensive), but they do exist. Just be sure to plug them in, in the right orientation (if you get one)!

Good Luck with your problem;

Stephen White