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Would you change your amp selection knowing...?

OK - so this thread was promted by some comments on another thread - not wanting to hijack that thread I created this one...

ISSUE: some high current designed amps have an issue with speaker cables that have a high capacitance.
- the amp can be driven to self destruction because of internal oscilation caused by the high capacitance of the speaker cable
- this does NOT apply to Tube amps - i.e. to my knowledge

The amps I know of that are affected in this way are Ayre, Gryphon and NAIM
- only NAIM warns of this up front AND instruct their dealers to let customers know about it

So why don’t other brands warn about the possibility?

QUESTION:
- would it put you off?
- would you select a different amp if the manufacturer warned of this "issue" up front?

Cheers



williewonka
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almarg
9,670 posts
 
@unsound
I found a link to the paper from which the excerpt shown at the link you provided was taken:

http://sound.whsites.net/cable-z.htm

My conclusion reading all of this is that I wouldn’t worry about his allegation that the resistor value chosen by Goertz is not ideal. As he even said, based on his simulations: (Comments shown in brackets are mine):
Even 100nF in series with 10 ohms restores the amplifier phase margin to normal.... 4.7 ohms is preferable, but the phase margin is barely affected. The speaker end response has a small ’lump’ with 10 ohms [between about 5 and 10 MHz!], and phase goes ’wobbly’ at above 20MHz. This is probably not a concern, and you will almost certainly get away with it.
I don’t, however, see any reason to doubt his statement that:
It is very evident that this particular cable [Goertz MI 1] should never be used without a Zobel at the speaker end....
Best regards,
-- Al

unsound
7,336 posts
 

Al, As I suspected.

 I thought I could count on you to illuminate this topic. Let me say that I am humbled that you went out of your way to research the hidden links, and offer your considered thoughts on the subject. I sincerely appreciate it; thank you.

cycles2
208 posts
 
Would speaker cables that use separate jackets for the + and - speaker have zero (no) capacitance?

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almarg
9,670 posts
 
Unsound, thank you kindly for the gracious response.  Cycles2, separating the two conductors as you describe will result in capacitance being very low, although not zero.  However, it will cause inductance to be considerably higher than if the conductors were in close proximity.  And in a speaker cable inductance is much more likely to be a significant factor than capacitance, aside from the situation that has been discussed in which cable capacitance is ultra-high and the amplifier is sensitive to that.

High inductance is particularly likely to have significant sonic consequences if speaker impedance at high frequencies is low (such as in the case of most electrostatic speakers) and cable length is long.  That is because the impedance presented by an inductance is directly proportional to frequency, and cable inductance is directly proportional to length.

Regards,
-- Al
 
213runnin
914 posts
 
I saw this thread and recalled a review of the Schiit Vidar amp when it first came out.  I think it was the computer audiophile site, and when the reviewer tried his 9 gauge cables, the amp started having issues.  

The reviewer sent the amp back to Schiit, they did some investigating and decided to make a change to the amp as a result.  Personally I don't see the need to ever employ 9 gauge speaker cables in any of my systems, but there you go.
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