Which cables cause issues for high bandwidth amps?

Cables having ultra-high capacitance are the ones that can cause the problem you experienced, if they are used without a properly configured Zobel Network. I believe Goertz can supply those networks, for use with their cables.

What "ultra-high" means, in terms of capacitance per foot, depends on the length of the cable, since the total capacitance of the cable is proportional to length. Following are what IMO are some rough ballpark guidelines for typical cable lengths, which are NOT based on any kind of precise analysis.

For typical lengths, I would start to become concerned if capacitance gets into the area of perhaps 600 to 1000 picofarads (pf) per foot or more, which equals 0.6 to 1 nanofarad (nf) per foot. Your MI-2's are 6000 pf/foot!!

For typical lengths I would not expect capacitances below perhaps 300 or 400 pf/foot to be a problem with nearly all amplifiers.

I would be increasingly cautious if the amplifier is one of those few having bandwidths in the megahertz region.

Regarding flat cables, yes, some of them have very high capacitance, but some do not. The Nordost's, for example, have extremely low capacitance, on the order of 10 pf/foot.

The great majority of speaker cables do not have ultra-high capacitance.

Regards,
-- Al

Thanks for the replies!

First, I am confident the cables were hooked up correctly. Also, I am now using the exact same set of cables with a Yamaha receiver and Monitor audio speakers and everything has been working fine for months, and the sound is pretty good.

Second, I want to see if I understand correctly that the spec that is the culprit in inducing these oscillation problems in amps is capacitance? And that as long as I keep that spec under 300-400 pf/foot, I am OK? Or, are there any other cable specifications that would ruin an amp?

Oh, also, the guys who are repairing my McCormack amp are discouraging the use of the Goertz cables, EVEN WITH the use of the Zobels across the terminals.

I want to see if I understand correctly that the spec that is the culprit in inducing these oscillation problems in amps is capacitance?

Yes.

And that as long as I keep that spec under 300-400 pf/foot, I am OK?

For typical lengths, say up to 12 feet or so, I would be confident of that. As I indicated, I am not basing that on any precise analysis, and a precise analysis would be dependent on the design of the particular amplifier. But I believe I am erring in the direction of being cautious, and so chances are that values that are somewhat higher than that would be ok too, at least in most cases.

Are there any other cable specifications that would ruin an amp?

No, I can't envision any other way in which a speaker cable could harm an amp, assuming of course that it does not have a short between the two conductors as the result of a defect.

Regards,
-- Al

I just don't get how one can get such huge per-unit capacitance in the cable and for what purpose?? There's also no specific disclaimer not to use with high-bandwidth amps... Who's supposed to be accountable for this kind of situation?