Weirdness with Moon Evolution 870A amp overheating on one channel with G2s
 

Here's a strange one:

Auditioning a Moon Evolution 870A amp with my Giya G2s. It sounded absolutely wonderful, but…

As soon as the amp was powered up, if the right speaker's mid/high cable was attached the amp would start to heat up like crazy. After only about two minutes the amp channel was over 15ºF warmer than ambient, and it eventually ended in the amp going into thermal shutdown for that channel after about twenty minutes. I actually burned myself on the amp when it happened the first time, a laser thermometer showing the other channel running at a nice 95ºF or so, but the right channel (that shut down) was at 205ºF!!

Why I don't understand this is if the cables are connected to any other amp I have handy (Levinson No. 334, Denon POA-8300 or Rotel RB-1552 Mark II) they have absolutely no issues driving the same channel.

Anyone have any ideas as to what's going on or why it doesn't happen with the left channel, or the right channel woofer, just the right mid/high, and why it doesn't occur with other amps?

I even tried connecting the right speaker's cable to the left channel of the amp, and then that channel went into thermal runaway, so it's definitely something about the right channel mid/high that it is having severe issues with.

Bill.......Are you running the woofer connected to speaker 1 output and the mid/tweeter to speaker 2 output, or are both the woofer and the mid/tweeter cables connected to speaker 1 output?

Also, are you using unbalanced or balanced interconnects between the preamp and the power amp?

Woofer connected to Speaker 1, High/Mid connected to Speaker 2. Once again weird that it would only have an issue with one channel though. Balanced cables between pre and amp.

Bill.......Have you tried swapping the left and right speaker cables to see if the problem follows the cables?

No, I didn't try swapping cables as my current amps have no issues and, biggest reason, swapping cables is a huge PITA on Vivids. :-)

Bill.......I know the G2's have their speaker terminals underneath and it is a two man job to get to them. I doubt seriously there is anything wrong with the speaker wires themselves but perhaps there is something unusual going on at the speaker terminals. I am just going through a process of elimination. It certainly is a peculiar problem.

That's the thing; were it the speaker or the terminals, I would expect one of the other amps to have an issue with it as well, especially one of the more mass-market amps.

The only thing I can come up with is either the amp is unhappy with capacitance in that particular run of cable, or there's something up with the speaker terminals or speaker that that amp is sensitive to and that cheaper amps work around (e.g. If this amp is direct coupled and the others have bypass caps.)

Bill.......What's unusual is the problem follows the speaker when you shift the wires to the opposite channel of the amplifier so it seems as though the amplifier is fine. It's a head scratcher.

Does the problem occur without playing music?

If the answer is yes then the amplifier is most likely breaking into HF oscillation.

And if that's the case it's possible that the combination of speaker cable and speaker's impedance is the cause. Is the problem speaker connected by a longer cable?

Nope, music needs to be playing.

Both cables (all four actually) are the same length.