In article , Iain M Churches
wrote:

"Jim Lesurf" wrote in message
...


The obvious point here is that most of the SET amps I have seen
reviewed in consumer mags have - where a value is given - o/p
impedance of around 1 Ohm even midband at low power.

I seem to recall than Andre told me they sometimes have a DF of 1.

If you mean DF=1 into 8 Ohms, that is a remarkably low (poor) value! With a
Quad ESL57 I'd expect it to produce changes in the frequency response of
over 10 dB if using the 8 Ohm o/p taps. Having such a poor o/p - LS ratio
might well also affect the distortion and peak power levels quite markedly.

Thus using such an amp rather than one with a low o/p impedance might
well change the frequency response by the order of 3dB. Hardly
surprising if this has an audible effect. Then a matter of
circumstances if this is preferred, I guess...

Yes indeed. I am still intrigued to know how an amplifier with such a
poor test bench specification can sound so good. I have no axe to grind
here. I do not own an SET amp.

From what you say, maybe you preferred the resulting frequency response
which would have been *very* different than when used with an amp with a
nominally flat response and a low o/p impedance.

A complication is that the 57 can provoke oscillations in amps that are not
unconditionally stable. The low and reactive speaker impedance can also
aggravate 'd.c. ducking' effects that can generate off LF effects as well
with musical dynamics. No idea if these have any relevance in this case,
though.

The difficulty of estimating amp-speaker interactions is that -
particularly with low-feedback and single rail designs like SET - a lot of
data would be needed to determine what *might* be happening. Alas, your
report, as many magazine ones, does not give the relevant information, so
we can't do more than speculate.

The CD player was a Studer A730.

OK. I don't regard that as likely to be particularly significant in
this context.

I mentioned it because I was sure you would ask if I did not:-))

Fair enough. ;-


Another interesting point here is that ESLs tend to provide lower
distortion than cone-and-box speakers. Yet SETs tend to provide higher
distortion than common SS amps.

At lowish listening levels, the SET distortion was not even faintly
audible. I daresay that at higher levels it might have been so. I was
not invited to touch the level controls, and did not do so.

OK. At low powers I would expect the distortions to fall and hence what you
say seems entirely plausible to me.

Slainte,

Jim

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