Solid State Amps for Quad ESL 57?

It's a bit tricky alright. Of course, you could put an air core inductor between the amp and the speaker to compensate, but that's tricky because it risks electronic resonances. Actually, it's quite unwise to attempt this unless you've made your own equipment to be bullet-proof.

The alternative is to compensate upstream, at the preamp or the cartridge step-up transformer. The obvious thing is to increase the capacitance of the 75uS RIAA compensation, starting by say doubling capacitance. Let your taste be your guide.

I should add, the Quad 2905's come properly compensated for solid state right out of the box. The 2805's less so. Re-working compensation for the 2905's is only necessary if you mess with the electronics.

Electrocompaniet 250R.

All the best,
Ari.

...I have used this combination before... the 250R will put yours quads to sing beautifully.

^^^^^
Electrocompaniet 250R.

Rated output power

8 ohms 2 x 250 W
4 ohms 2 x 380 W
2 ohms 2 x 625 W
1 ohms 2 x 1100 W

Power consumption (no load or signal) 230 W

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in comparison
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Music Reference RM10

2 x 35 watts
Power consumption (no load or signal) 70 W

The real story - imo - is how much the wattage difference grows between two when actually listening to music.

And

For those that do not have a dedicated space and can’t position speakers for the best High Frequency dispersion; Roger provides the "Quad Mod" feature on the RM10.

This is a Switch which is designed to lift (boost the response) from 2khz - 20khz. It’s a 3 position switch ( +1, 0, +2 )

The +2 position adds a boost at 2khz of 2db - This, and I quote from the RM10 owners manual.

"Brings the speakers to the brightness level of modern speakers."

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So you see; you really can have your cake and eat it too. Especially if your wife will not allow you to place the speakers in the room as designed for the most detail. Gets the job done, but I have to admit....

Not as funky looking as some of those external tweeters I have seen hanging off the speakers. Hey......I used to hang the things off the speakers myself .....in the earlier days. My external tweeter versions had no dial or toggle switch, but used actual resistors that I could add and remove for the desired brightness.

One benefit of those resistors hanging there; it made the speaker look more dangerous, so the wife would steer clear. Now if I can just train my kitty to stay away from them :^(