Solid State Amps for Quad ESL 57?

Yes, the Quad 57’s impedance curve clearly plays havoc with a lot of amplifiers, but I don’t understand the reasoning behind some of explanations for this. And at least one very basic factor about the amplifier/speaker interface is missing from this discussion-and quite ironically at that, as I will later show.

First, just today, a friend of a friend-both owning 57s-bought a used Atmasphere S30, being impressed with the overall design. But he found that it was a “terrible match” and gave nonexistent bass with the 57s.

Second, Atmasphere says that Bass is hard to get with transistors and Quads because many transistor amps will double power as you cut the load impedance in half. That’s quite true with amps like the Pass Labs XA series. And he says that the Quad has high impedances in the bass region and low impedances in the treble/HF region. "Most transistor amps would thus likely play the Quad 57s with weak bass and too much highs." Okay, that’s certainly believable criticism.

But then he says that the 57’s impedance in the bass is “…well in excess of 45 ohms. So transistor amplifiers cannot make power in the bass, while at the same time they make too much in the highs, where the impedance of the speaker is down to 4 ohms.”

Well in excess of 45 ohms in the bass? According to this obviously credible source, the 57’s impedance doesn’t rise any higher than about 33 ohms, and that’s at about 80Hz. http://www.quadesl.com/quad_main.html

Last but not least: Damping factor and bass response. In my discussions with Ralph Karsten he imparted some very valuable info on this subject. He said that high efficiency speakers (like my 97db 7 to 8 ohm two-way Radian 745 Neo/Be horn drivers/ GPA Altec 416-8B midwoofers) want a low damping factor amp-no more than about 20-like the S30 amp, otherwise midbass and certainly low bass will sound lean.

I don’t know what the S30’s DF is but low feedback amps tend to have low DF. Exceptions are amps like the Pass Labs XA30.5 and the new XA30.8.The Audio Research VSi75 has 4db feedback and ~ 4 DF. http://www.arcdb.ws/VSI75/VSI75.html But the S30 has only 2db feedback, so either amp would likely be a good match for my efficiency and all but flat impedance speakers.

Conversely, ESLs in general are at least 10db less sensitive than my hybrid horns.Soundlab recommends a 100 wpc amp for their smallest full range ESL model. More powerful amps tend to have lower output impedance and thus higher damping factors, again like the Pass Labs XA series, with typical DFs of 150. https://en.wikipedia.org/wiki/Damping_factor

Damping factors of probably at least 20, which is probably 10 times higher than the Atmasphere S30. No wonder my friend’s friend got no bass from the S30 driving his 57s. But again, the amp must have BOTH ample damping factor and a high impedance output; not so easy to find in most solid-state amps.

But guess what? The First Watt J2, though a solid-state, dc coupled, all JFET, Class A amp, with relatively low feedback indeed has a damping factor of 20. http://www.firstwatt.com/pdf/prod_j2_man.pdf And John Atkinson’s measurements

http://www.stereophile.com/content/first-watt-j2-power-amplifier-measurements#Uh4sMghuhX5g34Rh.97 Accordingly, the J2 not only prefers high impedance loads, but when the 57’s impedance drops to about 3 ohms at ~ 18kHz, the J2’s output power drops to about half what it is at 8 ohms. Thus, wouldn’t that keep the 57s from sounding bright?

All told, the J2 looks to be one of the very few solid-state amps that could actually play nice with the Quad 57s. If not, please explain.

They thing they don't tell you is what happens when driving higher impedances, like you see in the Quad ESL 57.   

Thanks Dover for pointing this out. I will have the 57s up on stands and adjusted accordingly-and at least close to this height, if my 14 ft x 19 room is big enough. I hope that Atmasphere and everyone will respond to my post about amplifier choices. I've certainly nothing against using tube amps, but I am curious about how well the J2 would work with the 57s. All the facts seem to support good synergy between them.

 I've run ESL57's both single, stacked and with sequerra ribbons

Dover, what are the Sequerra ribbons? Did you get these tweeters from here? http://www.sequerra.com/common/data/ribbon.html

http://www.sequerra.com/  Are they still available?

How did you integrate them with your Quad 57s? Did you disconnect the Quads’ own tweeters?

Is entire system still passively crossed-or are stock Quad 57s actually crossoverless? Or did you now have to bi or tri-amp it all?

Sequerra ribbons $$$? If beyond my budget, are there one or more tweeters that you might recommend?

Sadly, not yet. We were on for a Friday early last month until Jim got pneumonia. He said he was still very sick almost two weeks later. I’ll email him this week, see how he’s feeling and maybe we can set up for something this month, I hope.

Btw, I emailed Nelson Pass attaching the Quad’s impedance curve http://www.quadesl.com/quad_main.html and asked about using the First Watt J2 amp.

His reply seemed a bit vague, though he did say “the Quad wouldn’t hurt it” the J2. Later when I, more wisely, asked that of all his designs which First Watt or Pass Labs amp would make the Quads perform at their best in every way, he said probably the F6, F7 and J2. But he said what he really wanted to know for himself was how the SIT-1and SIT-2 would work with the Quads. Of course, that would be an intriguing session, but those two amps are somewhat more than I’d want to spend and run a lot hotter than the J2-which is hot enough for me.