Benchmark ABH2 amp and full range electrostatics, e.g. CLX or Soundlab


I have read the glowing reviews of the Benchmark ABH2 and have seen that Martin Logan has used these amps at Audio Shows with some of their hybrid speakers.  I would appreciate comments from audiophiles and/or reviewers who have significant experience with the pairing of the ABH2 amp with Martin Logan CLX's and/or Soundlab full range electrostatics.  Thanks in advance.
Ag insider logo xs@2xsoundhound
I have mono ahb2s and CLX Art. The amps have had no issues with the speaker bridged and also feeding 2 x rel subs. Amps are as transparent and lacking in color as anything I’ve heard. Replaced a luxman M900u which was very warm in comparison.
Thank you for this feedback.  I have Anniversary CLX's and had a concern regarding the ability of  single amp to properly drive these speakers and the higher output impedance of the amps when bridged.  Are you using a Benchmark preamp with these amps? Also do the Benchmarks produce a realistic soundstage in width and depth as well delineation of individual voices and instruments?
I started with a single AHB2 and it had no issues. I only added a second one because a used one kinda fell in my lap and it did bring an additional level of effortlessness that was worthwhile. 

As far as I can tell the Benchmark will simply reproduce whatever it's given and has no definable sound that I can discern. Soundstage width and depth are fully determined by the upstream source and recording not by the amp/pre. Likewise the overall presentation of the sound is determined by the recording and varies drastically. If you're used to components that intentionally inject a signature on the sound this may be hard to appreciate but for me it makes every recording a unique experience and world of fascination. 

I've done a ton of work on upstream components including external clocking in the digital domain and it has revealed every change. I've tried dacs up to $40K and have a similar amount in analog front end (Technics SL1000R / DS Audio Master 1) and so far have not been able to perceive any kind of bottleneck from the Benchmark gear.

I do also use the HPA4 preamp as well and it has a similar level of transparency. The preamp replaced a Luxman C900U.

Thank you kstaken again for your thoughts on the Benchmark/CLX pairing.  I have had a number of amps and preamps from Krell, ARC, Pass Labs and Constellation.  Having had Quad ESL's with careful component matching, ribbon tweeter and woofer which were extremely transparent and musical but frustrating in terms of limited dispersion and to an extent dynamic range, I purchased the CLX's a few years ago.  While I have not gone to the uberexpensive high end amps/preamps, I never felt that I had achieved the same level of transparency that I had with the original Quads.  I have ordered the Benchmark LA4 preamp. When my previously ordered Coda 15.5 arrives, I shall compare the ABH2 to the Coda.  I have had a Coda amp recently  and found it to be excellent and in many ways better than my previous amps in powering the CLX's.  You are obviously a careful listener and I am curious as to the cables you are using with the Benchmark electronics.  My experience has been that the CLX's are very fussy regarding speaker cables.

soundhound - Check out Douglas Schroeders review of the Benchmark ams(s) at Dagogo website . He used them with a full range electrostats .
I heard the Martin Logans with the Benchmark amp at Rocky Mountain Audio fest in 2018 . I coulnt stay in the room for very long though . They had an obnoxious volume level at the time . Sounded horrible to me . 
Maplegrovemusic,

Thanks for bringing the Schroeders review to my attention.  I shall look it up.  


Ahh, cables. Let me tell you a story about that...

Once upon a time ... I decided to jump into high end cables with a mix of Nordost Tyr 2 and Odin 1 believing their marketing of "delivering the depth, precision and nuance previously only found in live performances". While I had the Nordost cabling in my system every time I sat down to listen I fell asleep. It was like a drug, sit down, 5 minutes of music, zzzzz. It drove me absolutely insane and I changed everything numerous times, amps, preamps, dacs, turntables, racks, speakers but I never considered the cables because Nordost has such a reputation for being "transparent", "dynamic" and "revealing" and they were so stupidly expensive. Just in speakers alone I tried Martin Logan Electromotion ESL, Martin Logan Aerius ESL, B&W 804D3, Proac D30R, Magico S1, Devore O96, Devore Gibbon 3XL, Wilson Benesch Vertex, Martin Logan Impression ESL and others I'm forgetting. Tubes, solid state always the same result, zzzz. Finally I was sitting in utter frustration and wondering if I should just give up when it hit me that there was one thing I had never changed.

Went digging through my cable box and pulled out a cheap pair of Monster speaker cables and replaced just the Nordost speaker cables. The difference was unbelievable, the sound lost the "organic" feel that Nordost cabling imparts but it made me realize that "organic" sound was 100% a coloration and the price you pay for that is resolution and most significantly dynamics. To me the music lies in the dynamics, if you scrub away dynamics you scrub away the rhythm and the music dies. I realized in that moment that Nordost cabling makes the "sound" pretty but utterly ruins the music.

After this I went on a rampage and replaced every Nordost cable in my system. First I went anti-highend and used some lower end audiophile cables but as I learned the coloration they were imparting too, I went completely anti-audiophile and replaced all speaker cables and interconnects with Mogami pro audio wire and power cables with dirt cheap hospital grade cables that cost like $9 each. My system never sounded better, it was finally able to whisper and then roar and I stopped falling a sleep, and for a while I was 100% anti-audiophile cabling. This was the cabling I was using when I first received my CLX and I was actually perfectly happy with it.

Then on a fluke my local dealer got in a new line of cables from a company called Swisscables. Since I was still anti highend cables I reluctantly tried them and to my utter surprise they absolutely blew me away. More resolution, huge dynamic range and just a general feeling of being "right". None of the fuzzy fake organic quality of Nordost cabling just a feeling that the cable is simply allowing the signal through unmolested and allowing the source and recording to be revealed in their full glory. Needless to say I now use a full loom of Swisscables, Reference Plus for speaker and interconnects and Diamond for power. The only cable of theirs I've tried that I didn't care for was their digital coax which presented a bit of glare that I found problematic.

Sorry for the long winded response, guess I had some pent up desire to share this experience as I spent years being utterly dissatisfied with my system all because of a bad cable choice. 
Holy cow. Imagine if you tried some Synergistic CTS or Atmosphere. After all you been through you'd think you'd died and gone to heaven.
How I Learned to Stop Worrying and Love the Cables.
Kstaken,

I have had the Nordost Heimdall 2 interconnects and speaker cables which I have subsequently sold.  These cables have a definite sound of their own.  I used the Audioquest Niagara solid silver interconnects which I thought were more neutral.  My old Kimber KCAG's remain surprisingly good compared to current offerings.  I was fortunately to have a pair of Maker Audio Signature interconnects which are not usually sold in the U.S.; these are excellent but pricey interconnects.  I have not heard the Swisscables and do not see a retailer in the U.S. on their website.  

Speaker cables are another matter altogether.  The consensus seems to be that speaker cables for full range ESL's such as the CLX's and Soundlabs should have both low capacitance and very low inductance as these speakers behave electrically like a giant capacitor.  Coaxial speaker cables such as the Analysis Plus Big Silver Ovals have been recommended and there is a dual coaxial Mogami cable as well.  I have make some homemade speaker cables using relavitively costly Belden silver coated copper coaxial RF transmitter cables.  The main problem is that they are stiff but sonically I prefer them to the  Heimdall 2's.   I have not tried Wireworld speaker cables or the more expensive MIT cables which some have recommended.
I believe Swisscables are pretty new to the US. Arizona Hifi in Phoenix is a dealer and there are probably others around that work with the same distributer (wish I could remember their name).

These are not inexpensive cables but also not stupid level, maybe about Nordost Frey 2 price level. 

For another take from another Arizona audiophile they're discussed a little in this review: https://www.stevehuffphoto.com/2019/12/07/hifi-review-vinnie-rossi-l2i-se-integrated-amp-review-with-dac-a-magical-experience-awaits/ Steve is always a little over the top in his reviews but in this instance I agree with him.

The Mogami speaker cables I was using before were a Coaxial design and worked well but the Swisscables are just amazing (assuming your goal in transparency that is). 
Soundhound:
Go to PS Audio website, "Copper Magazine," and read the series of articles by Galen Gareis. (Something like issues 53 or 54-56 or 57. Alternatively, you could just go to the Iconoclast website and read their white papers. Galen Gareis is a former Belden engineer. The level of time and effort he appears to have put into researching and developing cables impressed me. Now sold under brand name Iconoclast, these include a speaker cable with both low capacitance and low inductance. Each model they make has three price options, depending on the grade of metal one chooses. The top of their line wires are not cheap (to me, anyway), but they make Nordost's silly pricing look like lunch money. Best of all, everything they sell has a 30-day, no questions asked return policy and no restocking fees. I just discovered this option quite recently and do not yet have any myself, but how can you go wrong? After all the half-million dollar record players and speakers we've seen in recent times (e.g., Mr. Fremer's recent fave $50,000+ tonearms), isn't it time for just a little bit of common sense in high-end audio? I am as obsessive as any audiophile and more than most, but one of the smartest things I've done is use my own ears more and worry less what high-end fashion dictates. YMMV
soundhound
Benchmark ABH2 amp and full range electrostatics, e.g. CLX or Soundlab
Should be fine, but I would not use a "bridged ABH2’s" (mono’ed) into these sort of ESL 1ohm loads, as the stability won’t be as good and the current ability to drive into low impedance will be halved.
If you have two ABH2’s and the speakers have two sets of speaker terminals then you could vertically bi-amp the stereo ones.
http://www.classicspeakerpages.net/IP.Board/uploads/monthly_2016_03/7_Vertical_Bi-Amp.thumb.jpg.672f...

Cheers George
George,

The CLX is not an easy speaker to optimize.  I had concerns regarding whether a single AHB2 amp could properly drive the CLX and like you whether the doubling of output impedance would pose a problem in regards to the very low impedance the CLX has above 8 kilohertz.  I have ordered an AHB2 amp will compare to my Coda 15.5 amp which is an excellent match.  Martin Logan has used bridged AHB2 amps to drive their hybrid speakers at various shows and apparently has not had a problem with bridged amps.  Nor has kstaken who in an earlier post on this thread communicated that bridged AHB2 amps are an excellent match with his CLX's.

Thanks for your thoughts.
jeffreyfranz,

I appreciate your suggestion.  I have done a little investigation regarding the optimal electrical parameters for full range electrostatics most of which behave like a large capacitor.  Roger West and Roger Sanders who know a bit about full range electrostatics have both advocated speaker cables with both very low inductance and low capacitance.  This is not easy to achieve.  Roger Sanders used to sell a dual coax speaker cable with such characteristics.  The Nordost cables published specs also have both low inductance and capacitance; I was curious about Nordost 2 cables and tried a combination of Heimdall 2 speaker cables and interconnects together in my system.  I selected the Heimdall 2 as a midlevel Nordost cable which would give me an idea of the signature of this brand.  They are excellent cables but have a distinct sonic signature.  I am aware of the Iconoclast cables but have not tried them.  They use Belden wire to fabricate their cables.  I looked at the Belden catalog and noticed that Belden Coax 8268 has 13 gauge central silver coated copper conductors and also very low inductance (0.077 microH/ ft) and low capacitance (30.8 pF/ft).  It is gotten expensive for raw cable, $6.90/ft from RF Parts.  I used xhadow spades for terminations.  It works surprisingly well and I found no advantage to the considerably more expensive Nordost and is perhaps slightly more transparent.  I cannot tell anyone else whether this cable will work in a given system but for full range electrostatics you might give it a try if you can properly terminate the cables and can deal with the stiffness of this cable. 


This is the problem you are up against.

Most ESLs have an impedance that ranges from whatever peak they have in the bass to about 1/9th to 1/10th of that at 20KHz.


Now imagine a well built solid state amp that can double power as impedance is halved.


Now comes the tricky bit- ESLs don't follow the same rules that box speakers do. To start with, there's no box :)  To further complicate things, their impedance curve is based on a capacitance (hence the falling impedance at higher frequencies). What isn't obvious is that in a box speaker, the expectation is that the impedance curve is also a map (to a certain degree) of its efficiency. For example, the woofer has a resonance in the box; this resonance is represented by an impedance peak. Into that peak the amp has to throttle back its power, which a solid state amp does because if it doubles power as impedance is halved, that means that it also halves its power as impedance is doubled. That works out nicely for flat frequency response when dealing with many box speakers.

But ESLs are different as I pointed out. Their impedance curve is not a map of efficiency; to reproduce a 100Hz tone at 90dB takes about the same amount of power as it does to reproduce a 10KHz tone at 90dB. You can see what will happen: an amplifier that can double power as impedance is halved will be too bright because the impedance is much lower at 10KHz as it is at 500Hz.


Martin-Logan has been sort of getting around this problem by making the impedances of their speakers very low; starting at 4 ohms in the bass and going down to a fraction of an ohm from there. Since many solid state amps (their intended market, since there are more solid state amps on the market than there are tube amps) can't continue doubling power into such low impedances, they sort of get away with it.

But with a Sound Lab, which is arguably the state of the art in ESLs, the 20KHz impedance is between 1.5 and 3 ohms depending on the position of the Brilliance control. A lot of solid state amps can drive impedances like that- but on the flip side, the Sound Lab is typically about 30 ohms in the bass, which means that solid state amps can't make power. So on a Sound Lab, a 200 watt tube amp can usually keep up easily with a 600 watt solid state amp on this account!

To further complicate matters, the human ear/brain system detects sound pressure by listening for higher ordered harmonics of any sound. For this reason the ear is keenly sensitive to higher ordered harmonics as it has to have a range of over 120dB. Both solid state and tube amps make distortion, but if you look at measurements you will see that the fundamental test frequency is usually only 60 to 100Hz, so we don't get to see what the amp is doing at 5-7KHz, which is where the ear is most sensitive  (the Fletcher-Munson curve, if you're still reading this far). So the higher ordered harmonics aren't shown. But if you are wondering why tubes are still around its because they sound smoother, and the higher ordered harmonic structure is why (not bandwidth!).


The ear converts all forms of distortion into tonality. The higher orders are treated as brightness and harshness. If you've been paying attention, then you know where I'm going with this- in addition to a brightness caused by a frequency response error on the part of most solid state amps on an ESL, you also get higher ordered harmonic content which the ear will also treat as brightness. Its a double whammy.


This is why ESLs and tubes have had a very friendly relationship going back to the very first ESL.  For more on this topic see
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
and like you whether the doubling of output impedance would pose a problem in regards to the very low impedance the CLX has above 8 kilohertz.
Yes and this is why you should get the "correct amp" that has no problem with this loading. And not gamble that bridged AHB2 are going to remain stable and handle the 1ohm loading.
As for tubes with this loading it is also why all the ones I have heard into my ML's have sounded "distant/muted" in the top end, lacking sparkle and air.

Cheers George    
George,

I agree.  The good point with the AHB2 is that Benchmark has a no questions asked 30 day trial period.  That should allow adequate time for evaluation.