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Sanders Sound ESL Amplifier Review

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Sanders ESL AmplifierI 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).

See the Other Review….

There’s no reason to spend a thousand words to describe the music I listened to with the ESL Amp, but if you haven’t read the 10B speaker review, then do so. Whatever I say about the sound of the 10B goes for the ESL Amp. If the ESL Amp weren’t good, the 10B is transparent enough that it would’ve told me it stinks (which it did on cables, amps, tubes, cartridge set-ups….you name it; if you get it wrong, you’ll know with the 10B).

What I do want to point out is that this is a primo quality amp for driving power-thirsty Magnepans. Until Roger’s ESL, the most powerful amps I had tried were 150-watt mono tube amps. They could play “loud”, but sounded forced and flustered when trying to recreate the sound and fury of the Beethoven 9th, Saint-Saens “Organ Symphony”, Der Ring Cycle, or anything by Shostakovich. By extension, this meant that I couldn’t rock-the-house with tube amps. No balls when listening to AC/DC, Metallica, The White Stripes, “The King James Version”, “Still Harry After All These Years”, and a lot of good stuff from Basie and Ellington. Sure, they could play Beethoven’s 1-8, any jazz quartet/quintet, “Kind Of Blue” and most pop music. Growing up around music, and having spent years in concert halls, I can tell you that music is often felt as much as heard. Regardless of what it might do to your hearing, a tam-tam at 50’ while the symphony is playing Stravinsky takes your breath away. It requires monumental amounts of power to try to recreate something like that, and 150 watts won’t cut it with the ESL 10B.

The ESL Amp delivered the goods when it came to reproducing musical peaks without strain. There’s a hot-rodding saying that applies here: there is no substitute for cubic inches. Even the “tricks” like supercharging are just making the engine hold the same amount of air that a larger displacement normally-aspirated engine would use. With speakers I’ve used, even the high efficiency designs, the use of a healthy power amp allows me to listen to all kinds of music, not just audiophile recordings of pretty girls. The intermodulation distortion of under-powered systems is something that you won’t hear until you get an amp of proper power. Once your ear becomes accustomed to hearing the IM distortion and compression, you can’t go back. I’ve heard 98dB single-driver speakers that compressed and got muddy, and not at what I consider realistic levels. That might mean an 833-based amp instead of a 300B for a horn. Maybe 150 watts for moderately efficient speakers. With the Maggies, it must mean that at least 600 watts is the minimum to sound relaxed. I’ve heard what a system can do with 3,000 tube watts driving 93dB efficient speakers, and the power was only sometimes needed. The ability to play peaks with no effort means less listening fatigue. Less IM and compression means more enjoyment.

That’s not to say that just any old, powerful amp is going to be “mission accomplished”. The mantra that power corrupts and absolute power corrupts absolutely is well applied to amplifiers. Few are the powerful amps that sound transparent. Many are the powerful amps that sound downright unmusical. Until the ESL, I’d heard only a couple other designs that had the openness and transparency of the tube designs I like.

I think one of, or maybe the thing, that makes the ESL Amp sound the way it does, is that it doesn’t use coupling (DC blocking) capacitors in the signal path. The only transistor amps I’ve heard that I liked were direct-coupled/DC-coupled (no coupling caps). Further, like the other transistor amps I’ve liked, it is balanced/complimentary/push-pull all the way through. This contributes to a dead-quiet nature of the ESL Amp.

Roger differs with my opinion and had this to offer: “Truth be told, the main reason that the ESL Amp sounds good has nothing to do with capacitors. It is due to the fact that it has no protective circuitry that ruins the sound when in operation. The output stage of the ESL Amp is so massive that it can never be taxed when driving difficult loads, so I can eliminate the awful audio effects of protective circuitry.”

Overall, the ESL Amp is one of the most neutral power amps I’ve had the pleasure of hearing. It’s very transparent. If you have something amiss, you’ll be able to hear it. Recordings have their sound amplified intact. There is no “sterile transistor sound” or pseudo-tube romanticism.

Macro-dynamics are very strong. Bass drum whacks are first rate. The plucked string is also very good, but not quite as jumpy as a SEDHT amp. There is some penalty for the extra devices and complexity, that seemed to be one of the trade-offs here: a penalty on microdynamics. Likewise, this amp isn’t as immediate as simple tube amps. It still has immediacy, but not on the level of the finest tube products. I could say the same thing about really big tube amps: not as much immediacy or micro-dynamics—very simple amps can do some things quite well.

Soundstage width of the ESL Amp is first rate, imaging well outside the speakers and placing a solid center image. It’s not as deep or dimensional as some competing thermionic designs, but it’s as good as any transistor amp I’ve heard.

Many of the stereotypes of tubes-versus-transistors have more to do with execution and design than any inherent weakness of the transistor (or the tube if that’s where you stand). At this level of performance, I am splitting hairs. The Sanders Sound ESL Amp is actually closer sounding to a powerful big-ticket tube amp than a “normal” 60wpc transistor amp. That’s what makes me consider the ESL Amp an enormous success. Outside of the user friendly qualities that Roger has designed into the amp, it does a tremendous job of amplifying a signal without changing its character. Considering the reasonable price, I think it’s an amazing product. If you need power, and most of you need more than you realize, you must hear it if it fits your budget.

As a follow-up to the review, I spoke with Roger about his other amps, and his response is in the following:

“Note that I now have my Magtech amplifier in production. It uses the same outstanding amplifier design as my ESL Amp, but incorporates a linear regulated power supply that is virtually 100% efficient. As a result, it produces much more power than the ESL Amp (500 w/c @ 8 ohms) even though it is in the same chassis.

Because the internal voltages are not modulated over a range of 30% (typical of conventional amps that do not have regulated power supplies), the distortion remains extremely low at all times (0.0012% typical).

There are virtually no amplifiers on the market that have regulated power supplies (only the Krell monoblocks at $100K are regulated). And the Magtech is the only amp that uses a linear supply that is essentially 100% efficient (patent pending). It would drive your Maggies even better than the ESL Amp.”

Sounds like Roger isn’t sitting still (pun intended).

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