In article , John
wrote:
On Thu, 13 Aug 2009 18:08:53 +0100, Dave Plowman (News) wrote:

In article , Eeyore
wrote:
You have my 100% agreement again. Is Jim Lesurf one of those
out-of-touch academics that never have to build a product that has to
work in the real world ?

I'll answer for Jim in case he's modest. He designed a variety of amps
for Armstrong which were very well regarded. I had experience of a
tuner amp which sounded very good indeed.

That may be so but all the guff about skin effect at audio frequencies
is only of relevance to the sport of measurement - you'll never hear the
difference.

I presume you missed the comments I made about this at the time.

However the page had two overall main purposes.

1) To investigate cable+load combination behaviour at ultrasonic/RF
frequencies that can, indeed, affect amplifier behaviour in ways that can
be both audible and measurable at *audio* frequencies. e.g. problems with
lack of stability into some presented loads.

2) To use the values obtained by the ultrasonic/RF measurements as one of
the methods to work out the cable capacitance, inductance, etc. Which again
can affect the results at audio frequencies in ways that can be both
audible and measurable. Did this because attempts to measure short run C
and L values are tricky at LF and also prone to the problem that the values
do alter with frequency. So did measurements by various methods to obtain
cross reference and reliability.

Skin effect was included, because internal impedance does indeed influence
behaviour and so is part of the above. In most cases 'skin effect' isn't
likely to be audible. But the difference it makes from one cable
design/length/load case to another might upset one amp audibly, but not
another. So it can matter.

If you have not already done so, I'd recommend you read the previous
articles in the series (hint: this one was 'cables3' :-) ) as that may help
make these points clearer. The 'cables3' article *is* part of a series, so
just reading the one page is a bit like reading one page of a book and then
complaining it doesn't make sense (because you don't know the context).

Slainte,

Jim

--
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