Using tube amp with electrostatic speakers.

A real nice tube amp for ESL’s is the Music Reference RM-200 Mk.2, designed and built by Roger Modjeski, an amp maker who is also an ESL speaker expert. Roger currently makes his own ESL’s, and was involved in the design of the legendary Beveridge ESL’s of the 1980’s.

The RM-200 Mk.2 uses only two KT-88 (or similar) output tubes per channel for 100 watts each, and does so without running the tubes hot or hard. One of the bargains in hi-fi, $4200 new. It imo resides in that perfect price vs, performance sweet spot. Currently in Stereophile’s Class A Tube category.

Erik, Music Reference’s phone number is still the Santa Barbara one (805)687-2236, which will go to Roger’s voice mail. His email address is [email protected]. Wish I could join you! I miss the Bay Area, having grown up in Cupertino/San Jose, coming into San Francisco for gigs, and to go to The Fillmore and Tower Records. Very expensive to live there now! Is Village Records in Mill Valley still around? Used to be a great store for Roots Music.

Roger has opened an Audio Engineering school in Oakland (I believe, though it may be Berkeley), wanting to pass on his electronic expertise to younger designers and audiophiles. The Music Reference model (with prices) page on the website lists the ESL speakers, and a bunch of new, low-power amps. OTL’s, Single Ended, etc. Roger is a really creative and knowledgeable tube amp designer.

From my reading, I am aware of another consideration in these matters. The way an amplifier circuit reacts to very high frequencies presented to it, frequencies too high to be heard on their own, can affect the behavior and sound of the amp. A barely-stable circuit can be driven into oscillation by those frequencies, creating ringing and different forms of distortion.

Frank Van Alstine and Roger Modjeski have discussed this area of amplifier design in their writings, and it is an important consideration with ESL loudspeakers. They benefit greatly from an "unconditionally" stable amplifier. Both Frank and Roger make such amplifiers, though they are not alone in doing so.

Good info Lew. Yup, 14k is inaudible to me too now, thanks to over fifty years of performing and attending live shows, some with excruciatingly loud SPL. I had molded ear plugs made when I was in my 30’s, but the damage had been done. Youngins’, don’t put it off, use protection!

Stewart, ESL's and Magnetic-Planar loudspeakers present quite different loads to an amp, ESL's a very reactive one, M-P's a resistive. In addition, ESL's benefit from a voltage source type amp, M-P's a current source design. That's why Roger Sanders makes an amp for each type loudspeaker. Right Lew?