Richard Clark $10,000 Amplifier Challenge - Why Couldn't Anyone Pass this Test??

Wow, what a great post from Ralph/atmasphere. As always!

+1.

Also, while it doesn’t directly affect anything that was said in Ralph’s excellent post, to be precise I would just add that Ohm’s Law and the stated definition of power apply to resistive loads. And to the extent that a speaker’s impedance is partially capacitive or partially inductive at various frequencies the amount of current corresponding to a given power consumption by the speaker will differ somewhat from what Ohm’s Law would predict for a resistive load having the same impedance magnitude (i.e., the same number of ohms). In particular, impedance phase angles that are highly capacitive at some frequencies can increase current requirements to a significant degree, at those frequencies. But not by nearly as much as some manufacturer literature and some reviews might lead us to believe.

Best regards,
-- Al

Then to just complicate what I said above, the current output of an amp comes into as well, to keep the said control over the speaker.

This is a common myth.

An amplifier can have a very low output impedance without having much ’current’.

Ralph you jumped the gun mate, read again, I never tied output impedance and current output together in the same sentence.

Cheers George

I was going to write some quibbles, but instead I will just point you to this article from Roger Sanders. While the amp he talks about has long been superseded, the problems about ESL's and phase angles and currents remains true.

http://www.enjoythemusic.com/magazine/manufacture/0702/

Best,

E

Also to add, an amplifier "with low output impedance", but with not much "current ability" like otl's, have no chance driving a pair of Wilson Alexia's and like, which drop to an EPDR of  .9ohm around 100hz (the power region) without serious problems.

Cheers George      

It has long been considered common wisdom that OTL amps are great with the original QUAD ESL. When I had just gotten my first pair of the speaker, I asked Roger Modjeski at an instore seminar for his view on amps well-suited for the QUAD. He had worked on many Futterman amps, and in the 1980's designed his own OTL, which he ended up selling to Counterpoint. He also worked on the direct-drive tube amp used in the Beveridge ESL, fixing some problems he found in the amp when he went to work for Bev. Roger said that though the OTL/QUAD combination was indeed considered by many to be a good synergistic match, he considered it to be the opposite---an OTL being the absolute worst amp design for use with that speaker. The reasons included the matter of the impedance swings in the speaker, of course. Roger has designed and currently offers an ESL with a direct-drive (no speaker transformer) tube amp, which I am dying to hear.