ESL AMPLIFIER MARK II Martin Appel, reviewer

Print, November 2002, Martin Appel, reviewer

Roger Sanders, the head man at Innersound informed me that he'd come out with a Mark II version of his much heralded amplifier and asked if I'd be interested in reviewing it. I responded, "How fast can you get it here"? 
Let me back track a little bit. I did the first review of his original ESL amplifier in 1999, for my former magazine, and I was so taken by it that I bought it and it became my reference. Many of my colleagues had similar reactions and even "the great one", Harry Pearson, of The Absolute Sound, gave it his "Editor's Choice" four star rating, in Issue 125. High praise indeed.

Now Roger Sanders, whose been designing speakers and amplifiers for over 30 years was not about to sit on his laurels. Ever the tinkerer, he sought ways to improve an already excellent product. 

First, let me summarize Roger's concept of amplifier design. Roger's approach is that what gives most solid state amplifiers that "transistor sound" is the way they clip. Given enough clean power and eliminating the use of protection circuitry, which can also contribute mightily to that "transistor sound", one avoids clipping and all the musical information comes through in its entirety. To do this he gives us an amplifier that produces 300 watts/channel at 8 ohms, 600 watts/channel at 4 ohms into conventional loads and 2000 volt-amps/channel into electrostatic loads. This is surely enough power to drive any type of speaker. 

He does this by using 18 output transistors per/channel, each one capable of 250 watts, totaling an astounding 4,500 watts/channel and a bandwidth of 10 Mhz. (To actually achieve 4,500 watts, according to Roger, it would be necessary to have a power supply four times the size of the amp.) As you can see the amplifier operates well within its operating range. What makes this all even more amazing is that the amplifier only weighs 42 lbs, runs cool, and I do mean cool, with midget sized heat sinks and costs $2,995.00 US. (For further technical description go to InnerSound's web site at 

The following was Roger's response to my query as to what the differences were between the original ESL amplifier and the Mark II:

There are three differences between the original ESL amp and the Mk II version. 

1) We replace the original Mitchell speaker binding posts with German, WBT binding posts. The WBT posts have the advantage of being keyed to the chassis so that they will not rotate. Unlike most posts that have round shafts, the WBTs have a square shaft so 1/4" spades don't rotate on them. If a spade rotates when being tightened, its gold plating can be torn loose, leaving a contact that can oxidize over time. The WBTs also have an anti-rotation section above the spade so that rotating the knob to tighten it will not cause the knob to rotate against the spade. Again, this prevents damage to the spade's gold plating. Finally, the WBTs are simply better-looking and have higher quality gold plating than the Mitchell posts -- in other words, they are the finest German quality. 

2) The Mk II amp uses global feedback. The original ESL amp had a small amount of local feedback and no global feedback. This was done to satisfy the demands of some audiophiles who believe that global feedback is bad and must be avoided (this is not true, but their perceptions are our reality). 

However, the lack of global feedback meant that there was no feedback used in the output stage of the amplifier. So to keep distortion low, we had to use more bias than would otherwise be necessary and the amp's damping factor was higher than what it would have been with global feedback. The result was that the amp ran warm and didn't control the bass quite as tightly as one would expect from such a powerful, solid-state amplifier. 

Despite some audiophile opinions regarding feedback, the fact is that a MODEST amount of global feedback, that is PROPERLY COMPENSATED at high frequencies, improves amplifier performance in every way. It does this without any adverse affects of any type. So we decided to add a small amount of global feedback to improve performance and take our chances with audiophiles opinions. As expected, this significantly improved bass control and "tightness." It also dropped distortion to immeasurable levels. This allowed us to turn down the bias even further with the result that the Mk II amp now idles completely cold. 

3) Because waste heat is now virtually non-existent, there is simply no need to turn amp on and off. Therefore, the front panel power switch was moved to the rear panel. This "cleans up" the front panel and improves the appearance of the unit."

Now that's straight from the horse's mouth. Take it or leave it. Well this reviewer has to report that Roger's design changes have taken an amplifier from excellent performance levels to startling. If I could briefly sum it up in one word it would be clarity. This amp is as neutral and accurate to the source as one could hope for. Garbage in, garbage out, they say. In this amp's case is this ever true. If you want euphony, or what some audiophiles call "musical", this is not the amp for you. I don't mean to imply that it sounds hard, dry or etched either. But if you really want to hear what's going on, on the recording, and hear all the music that's there, than this is the amplifier is one to be taken very seriously. 

How did the Mark II sound vs. the original?  Starting out at the frequency extremes is always interesting and telling. High frequencies as produced by symbol strikes of Louis Nashe's drum kit, or Ali Ryerson's flute, or Dizzie Gillespie's trumpet, were very informative. The Mk. II didn't appear to extend further than the original, but there was more information to listen to. Notes had more texture and inner detail. There seemed to be just a little more air in the shimmer of the symbols, as well as more resolving power to hear the components of the sound being created by the instruments. By having this additional clarity and information, the instruments came to life with more real musicality and ease than previously heard before. 

Let's look at the other extreme, the world of bass. It was clear from the first notes I heard that Roger's efforts had born fruit. All the comments I made about the high frequencies were mirrored by the bass frequencies. There was improvement in impact and palpability in Ray Brown's bass and as well as more air around the instrument than before. The detail of fingering was more apparent. The same held true for electronic base and drums as well. Kettle drums, at the orchestral rear had visceral impact and definition. Mallet strikes were clearly defined with accompanying reverberation and natural decay. You clearly heard that kettle 'cookin'.  It was just more believable. Ah, there goes that clarity thing again. When those double basses play in the opening few minutes of Liszt's Hungarian Rhapsody No.2 on RCA's Living Stereo conducted by Stokowski, their 'woody', resinous quality, resonates through the floor, up through your feet and into your gut. 

There's nothing that tells the story better, as far as the middle frequencies go, then listening to the human voice. Whether listening to Frank Sinatra, Diana Krall, or Shirley Horn, the textures of notes and individual characteristics and nuances of each note was so clearly expressed that it became apparent what each singer was trying to express. The emotions were right out there for you to feel and these artists were communicating it to you. 

All the typical audiophile parameters were handled with aplomb by the original and slightly bettered by the Mark II. Sound staging was wide and deep with plenty of air. Dynamics were there in abundance. Orchestral works really were more convincing than ever taking you one step closer to the concert hall. Again, if the recording had it, you heard it: chairs squeaking, musicians moving, breath intakes, sheet music being turned, etc. What this detail retrieval also meant was that you heard all the instruments in the orchestra, making music, not just a blending of musical noise. This was not done at the expense of musical enjoyment but gave one a heightened appreciation of the music and musicianship. "Musicality" anyone?

Now amplifiers do not exist in a vacuum but are part or a system in the audio chain. I've recently added new pieces into my system which will generate upcoming reviews. You've already heard from me about some of the outstanding cable products by Acoustic Zen. I've been using their latest digital cable, Silver Byte into a new DAC by Birdland Audio, the Odeon-Ag, from their Silver Series. The signal is then travelling into a new preamplifier by KORA Electronic Concept, a French company, the Eclipse, a remote controlled triode tube full function unit that will also get the full review treatment. All of these new pieces were in place when the Mark II came along. 

This proved to an ideal situation since I could listen and evaluate the sound with only changing one variable, the amplifier. It is often difficult, if not erroneous, as a reviewer, or serious hobbyist, to make judgements about pieces of equipment while simultaneously introducing two, three or more variables into a system. Either not giving those pieces enough time to really burn in, or not isolating the characteristics of each piece, individually, to properly determine what each is contributing to the overall system sound. Either could lead to premature and/or inaccurate judgements.    

Anthony Kershaw, our esteemed leader, just gave a rave review to the Burmester 911 Mark III power amplifier in the previous issue anointing it with a well deserved star rating. Part of the problem for reviewers is that one is unlikely to be able to compare all the fine equipment out there head to head and we can only go by our own experiences in making recommendations. The InnerSound ESL Mark II, at a little less than one sixth the price of the Burmester, would receive my star rating for extraordinary performance and value. I would love to be able to insert the Burmester in my system and invite my audiophile buds over for a good shoot out.