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Which cables cause issues for high bandwidth amps?

As in, blow them up? I recently bought a McCormack amp and blew it up when using Goertz Alpha Core MI-2 cables. I am about to get the amp back from being repaired, and I want to make fricken sure that I don't repeat the episode. Now, I do have a feeling that there was something wrong with that amp in the first place, but I still want to be very careful.

I now know that using the Goertz was a no-no, but I am told there may be other brands of cables with the same concerns. I have been advised to stay away from "flat" cables for the McCormack. Is this true, or an over-generalization?

I am looking for moderate price options, if anybody has experience with cables that sounded great with McCormack amps. Thanks a bunch!
mtrot
almarg's avatar
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almarg
9,670 posts
 
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
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marakanetz
5,473 posts
 
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?
rlwainwright
1,904 posts
 
My H/K Signature 2.1 amp did NOT like my Goertz MI-2 cables until I installed a Zoebel network across the terminals of the speakers. However, my Gallo 3.1/Butler amp combo seems to have no problem with it. Apparently the MI-2s with certain speaker/amp combos will cause the amp to go into oscillation...

-RW-
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almarg
9,670 posts
 
Correction: I misread the Goertz datasheet. The capacitance of the MI-2 is 950 pf/ft, which is still very high of course.

Marakanetz, the high capacitance is a side effect of their approach to achieving their primary design goals, which were ultra-low inductance and ultra-low Characteristic Impedance.

Whether the ultra-low inductance is overkill or not, and whether the ultra-low characteristic impedance is likely to provide any benefit, are debatable and most likely system dependent, IMO.

Regards,
-- Al
bojack
630 posts
 
Man, I would not even THINK of using the same cables when you get your amp back! 12ga stranded will work fine IMO.
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