dal Colorado con amore per la musica
di Francesco Bollorino
Oct 2007

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Roger Sanders has been a big name in American hi-end audio since 1974.
Several years ago he founded InnerSound, a famous maker of electrostatic
loudspeakers that received great press reviews in the US and throughout the world.

He ended his participation in InnerSound in July 2004 and has now started his own company based Colorado, were he designs and sells a new line of amps (derived from his Innersound products) under the SANDERS SOUND SYSTEMS label. These amps are specifically designed to drive difficult loads like electrostatic loudspeakers, which he obviously knows very well. He therefore calls the amp the "Electrostatic Amplifier" (commonly called the "ESL amp"), although it will drive any type of speaker with ease.
I had read some literature on-line about his products and I was quite curious as I own a pair of Quad 988s. I am convinced that sometimes we can find better solutions to the setup we already have, which in my case is a pair of OTL tube amps especially built for QUAD.

With a little luck and intuition I decided to contact Roger Sanders and I had one of his ESL amps sent to me for a trial. I choose the smallest one of his line, a "little" stereo amp rated at 360 watt per channel. He offers power amps that go to more than a kilowatt at 8 ohms in the mono version.

Roger also produces line-stage and phono preamplifiers and electrostatic speakers. Also available are quite inexpensive interconnect cables and speaker cables that are specifically designed for electrostatic speakers.

Roger is an engineer and has scientific approach to hifi, (Okay, he doesn't believe in cable influence from a physical point of view and in all my theories on fuses, but he is very nice and down-to-earth and I was very sorry I couldn't visit him during my trip to the U.S. last summer). I had several long e-mail exchanges on the philosophy behind his products and I will try to summarize them here for my readers.

His first theory is that no matter how good a tube amp is, it is not the best feed for an ESL (ElectroStatic Loudspeaker). This is because if it is played loudly, it will go into clipping, which produces high distortion levels, loss of detail, and compression of the music's dynamic range.

Tube amplifiers also have relatively high output impedance. Since you cannot drive a low impedance load with a high impedance source, most tube amps will cause a loss of high frequencies when used with ESLs.

This is because an ESL's impedance is inversely proportional to frequency, which means that an ESL's impedance will be very low (typically 2 ohms) at high frequencies. So the relatively high output impedance (4 ohms for example) of a tube amplifier will cause non-linear frequency response in an ESL.

Second point is that in order to obtain good sound from an electrostatic, we need undistorted power and flat frequency response across the entire audio band. This can only be obtained with high-power, transistor amplification.

To my question, "Isn't your amp too powerful for my Quads?" Roger answered that in my case, in order to play well, I need much more power than I think I need. He has sold several of his powerful ESL amps to Quad owners and none had ever returned the product or had problems with their Quads because of the amplifier. They all thought the ESL amp worked beautifully.

According to Roger, the most important parameter in an amplifier is sufficient power. The amp simply must not clip under any circumstances as doing so will cause loss of dynamic range, distortion, and loss of detail. It is for these reasons that it is better for an amp to bring the loudspeakers to their limit rather than going into clipping before reaching that limit.
First, some comments on specifics and build quality. The pictures are quite explicit of all but an artisan built object made in USA. The amp has a very high quality external finish. The internal and connection components are superb (WBT connectors for the loudspeakers, 1% tolerance components, RCA connectors in rhodium, 18 transistor power for each channel, machined aluminum chassis, shielded toroidal transformer, etc.).

The amplifier has excellent performance specifications with 360 watts/channel at 8 ohm, 600 w/c at 4 ohms, and over 1000 w/c at 2 ohms. The amp can produce 2000 VA per channel when driving an ESL. It has 26 dB of gain, 500 volts/microsecond Slew Rate, and an input impedance of 50 kohm. Distortion is vanishingly low at around 0.002%. It weighs 23.5 kilograms (52 pounds).
The designer recommends keeping it always on as it runs cool and consumes very little electrical energy at idle. Leaving it on contributes to high reliability, long life, and the unit will always be warmed up so will operate at its best the moment you wish to use it. For this reason, I started my listening after a warm-up period of 48 hours with the power line filtered by DOCET of which I spoke in the most recent issue of this magazine.

I used SONIC EUPHORIA and ZOE by Lector as preamps. My source was a CDP OPUS 21 by Resolution audio. The usual cables: Dual Connect for the loudspeakers, YBA Crystal between the preamp and power amp, the great SILTECH COMPASS LAKE G6 SATT VERSION between CDP and preamp, AC cables by Siltech for the Quad and by Crystal Cable for the other components.

When I first started listening, I was quite traumatized. The Quad protection circuitry kept triggering. But once I figured how it worked, I found just the right volume to avoid the triggering the protection circuitry. Thereafter everything went smoothly so I could start critical listening of my made-in-Colorado amp.

I immediately was struck that Quads have a greater extension across the entire audio band when being driven by the ESL amp than when driven by my reference OTL tube amp. The low frequencies are definitely deeper and much more controlled, and the high frequencies seem endless to the point that I had to remove the supertweeters by Mark & Daniel, which were no longer needed.

When driven by the ESL amp, the Quads produce high frequency response that I have never heard before. The highs are not at all tiring. Rather the information is much more complete and produced with more coherence than before.

Mid-range and voice have the usual Quad magic, but are now softer with richer harmonics up and down that give the sound great realism. Compared to the OTL tube amp, response speed on transients is definitely greater. The imaging maintains good proportions but now appears deeper and richer with more micro-ambient information.

Instrument positioning is realistic and differences in registration is much more defined than previously. Resolution is greater, which makes differences in speaker positioning and electronics easier to analyze and evaluate.

I might say that the ESL amp is a little less "warm" compared to the OTL amp, but it gets along well with Quads, which produce better coherence and a clearer and more realistic sound than that produced by the OTL amp.

The interface of the ESL amp with my two preamps was excellent. The Sonic had a chance to show its legendary adaptation to the new amp showing all its best assets, especially in sound stage reconstruction and voice rendering. ZOE made reproduction a bit more aggressive when necessary thanks to greater speed and gain, ending up to be my favorite between the two in an interface of tubes and transistors of rare efficiency and magic.

I had tried other amps in the past with the Quads, but not even the Threshold amp gave me the performance of Roger Sanders' ESL amp in terms of comprehensive performance. Until the arrival of the ESL amp, no previous amp behaved better than the OTL amp with the Quads.

But there is a first time for everything. The obvious conclusion is that I decided to buy the ESL amp as it made a great improvement in the overall quality of my system. Maybe I could find something better for the Quads but I doubt it would cost less than the 2900 euro I spent to buy this amazing music machine in the USA.

I realize I was privileged to be able to try in my home the ESL before deciding to buy it, and I can understand that the lack of an Italian distributor is an obstacle to its distribution in the Italian market. But still, I must recommend it as a great price/quality bargain and as a well-engineered and quality-built product. I usually don't recommend or approve blind purchases but . . . exceptions can be made.


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