I consider this more of an addendum than a proper review. I had the ESL power amp for use with the 10B speaker system. The 10B comes with electronic crossover and built-in bass amp, but you had to supply your own amp for the electrostatic panels. I had some tube amps on hand, but the load presented in the highs would cause high frequency roll-off. The impedance drops to 1.6 ohms at 20 kHz. I had an amp from Plinius, but the combination sounded bright. I wasn’t expecting it to be bright and couldn’t figure out why. Roger suggested it was possibly an oscillation caused by the wrong kind of speaker cable and an unhappy capacitive load for the big Plinius. I tried some video coax for speaker cabling since it was shielded and of very low capacitance. I still had the same tonal balance. I wanted to hear the same combination I had heard at CES 2009, so I contacted Roger about sending the ESL Amp to complete the system.
Outside of a powerful tube amp (at least 120 watts), I can’t imagine a better amp to drive an electrostatic loudspeaker than the ESL Amp. Roger thoroughly addressed every pitfall of driving ESLs, and did so with a transistor design. It would’ve been easier for Roger to design a powerful mono tube amp of generic design, say parallel push-pull sweep tubes for 200 watts. Tube amps don’t oscillate when driving the very high capacitance loads presented by ESLs. They just lose steam in the highs. In the end, Roger’s ESL Amp has flat frequency response, is several orders of magnitude more efficient, generates almost no heat, is housed in one chassis that can be situated almost anywhere and can be left on all the time.
What’s more important for this article is how it sounds with other speakers. To wit, how does it sound driving the incredibly inefficient and low impedance Magnepan 2.6R? I’ve had these speakers for years, and after modifications (updates), still enjoy the sound. On the other hand, I always felt as if I needed WAY more power.
The ESL is rated at 2000 volt-amps, which is similar to a “normal” 1000-watt amplifier, see here for an explanation. The volt-amp rating applies to capacitive loads. With magnetic speakers, the ratings are more typical, though still quite powerful:
·300 watts/channel into 8 ohms
·600 watts/channel into 4 ohms
·1000 watts/channel into 2 ohms (momentary/dynamic output)
If this isn’t enough, there is the mono version that delivers 800 watts into 8 ohms and 1200 into 4 ohms.
I found out from Roger that the ESL has been slightly upgraded and uprated:
“The latest version is 360 w/c @ 8 ohms, 700 w/c @ 4 ohms, and mono it is 1000 watts at 8 ohms and 1600 watts at 4 ohms. I need to update my website! The amp you tested was the original version.”
For the sake of saving time, and touching on the technical issues, please refer to the “ESL Amp White Paper” on the Sanders Sound website.
I can say that none of the statements are snake-oil ramblings, or marketing hyperbole. I left it on for months, it was always quiet, it drove the crap out of anything I connected to it, and it seemed to have no distortion (that I could hear).
