In article , John Phillips
wrote:


I learned a lot from designing and building my first power amplifier. I
saw undesirable behaviour into the many MHz region whenever I failed to
pay enough attention.

Indeed. In fact there are two stages to this.

1) The designer has to be able to establish if his bench design is
unconditionally stable or not. And if not, modify or change, to obtain
unconditional stability, without fouling the performance in some other way.

2) To then ensure that this will be true for commercial versions made with
components with a tolerance spread of values, slight alterations in
wirings, etc.

The worry here is the 'WW' effect. That of designs where a prototype
(published in Wireless World for example) worked fine for the designer. But
when many readers make 'clones' some of them oscillate or misbehave in use
due to changes in precise component values, wiring, etc. Hence the old term
'a WW design = a Worked Wunce design' to refer to this possibility. :-)

So, I'm surprised at your reaction elsewhere. Even in the audio band,
loudspeakers can present impedances from near zero to high enough to be
considered infinite. Out of the audio band this gets no better, from
what I have seen.

So it seems to me that investigating loudspeaker cables with loads from
zero to infinity, and at frequencies well above the audio band, is
perfectly reasonable.

There are two aspects of this that have concerned me. One is that I am far
from certain if all current/recent commercial designs are unconditionally
stable - particularly as I don't see signs that any reviews routinely check
this.

The other is the lack of any info on what speakers do above the audio band.
When you then throw in a variety of types and lengths of cables, almost
anything could happen in some cases.

I chose to measure an LS3/5A as I had a pair to hand. No idea what other
speakers do above the audio range. There seems to be zero data. I doubt the
makers usually know or care.

BTW Given Eeyore's reaction I'd suggest people read the previous two
'cables' articles in the series as that did cover some points. e.g. the use
of output networks. Although more about this and other factors will be in
later articles.

Slainte,

Jim

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