Amplifier for Quads

I agree with Charles1dad; Roger Modjesky designed his RM-10 specifically for his own Quad ESL-57s.

I 've owned both the Bedini 25/25 and currently the Atmasphere S30 though I have not heard either with Quad 57. I can say that the Bedini 25/25 is highly regarded by Quad 57 owners as I was deluged with offers when I sold it.
That being said, I would second the recommendation for an Atmasphere OTL. Would recommend the M60 but you could use the S30 if the stacked Quads were wired in series (increasing the overall impedance).

Agree completely with Charles1dad. In fact, I have been told by more than one Quad 57 owner (I never owned them) that the Quads actually seem to be able to play louder with smaller amps like the Bedini, but particularly with quality tube amps, instead of big powerful ss amps. Go figure.

Fair enough. I'm just so impressed with Roy's work, I thought I'd share my experience.

The classic combination with ESLs since the 1950s has been ESLs and OTLs.

The impedance curve of the speaker is benign. The advantage that OTLs offer is that there is one less transformer in the signal chain so its more transparent. The other thing is that OTLs don't have any problem making bass on the speaker. In the bass region, the impedance of the speaker is so high that this is a problem for a lot of amps. This is why transistors don't do so well with them.

A minor correction: The Quad should not be driven by amps that make a lot of current, they prefer amps that make **power** (not just voltage). This means a tube amp, generally speaking. For more information about this see

http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php