In article 4a833da4.554360703@localhost, Don Pearce
wrote:

So here's the thing. For the consumer, knowing the impedance of a cable
is not important,

I'd say "*should* not be important", but with a concern that a cable should
not have an unusually high series impedance or shunt capacitance. Most will
be fine, though.


although it is clear from Jim's work that you are less likely to run
into trouble with some than others. But the article should be a wake-up
call to anyone in the design business that a blinkered, audio-limited
view can be a recipe for a very poor amplifier, whatever the
measurements may say.

That is one of the concerns I have. I'd be happier if reviews checked
stability, or at least got makers to state if their product was
unconditionally stable. I think it likely most (and probably almost all)
are. But what about the off-the-wall designs with high output impedance,
etc? Are they all fine? Who knows? I certainly don't.

The other is that in some cases people may be paying for cables that, say,
have a high enough series impedance to audibly alter the sound, and then
presuming this was because it was a very expensive cable made of
unobtainium - but where a cheap resistor and/or inductor would have had the
same result. Ditto for a cable with high shunt capacitance used with a
valve amp that has an output impedance above an Ohm. Yes, some do have
such high output impedances. Is it a reflection of high impedance inside
their feedback loop (inc transformer)? I don't know. Who does?

I'm happy enough just to get people thinking about this rather than leaving
it in the dark corner its been left in out of sight of the public for
years. If that leads to people finding that all the current/recent
commercial amps are fine, that is an excellent outcome from my POV. If it
gives some designers a 'heads up' that also suits me fine.

Back, say, in the late 70s or early 80s it was routine to check stability.
Since then it seems to have slipped though being taken for granted into
neglect. Has it been forgotten by some? From the reactions I've had here I
have the uneasy feeling that, yes it has by at least some people.

Slainte,

Jim

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