[steve f]

I was talking to a design engineer about Class D amplifiers. He said they didn't work well with some ESL speakers.

I used a Crown XLS 1500 on my Quads with no problems. What is your experience with Class D and speakers capable of ultrasonics? Some people use only AB or H amps in solid state.

[Blackmore]

I tried the little TBI on the stat panels of my Innersound Eros and it made a loud buzzing/whining noise with no signal applied.  Only amp to have trouble with the Eros, so I assumed it just didn't like something.  I've driven the panels with SS, SET and push pull with no problems. 

[mcgsxr]

I am currently running Maggie MMG's off a Crown XLS 1500.

Works a treat.

[steve f]

Blackmore, that's interesting. Was that the only Class D amp you tried?

[Blackmore]

So far the TBI was the only one, but I do have a couple other low power digital amps to try but the Innersounds aren't in the system right now.  Could have been just bad karma that day, but I wasn't encouraged to try other digital amps on that speaker.  Next time it's in the living room, I'll try the other amps I've got. 

[steve f]

mcgsxr,

It's a different ballgame. The Maggie mmg is pretty much a benign four ohm load. Some ESLs get under one ohm, and are capacitive too.

[Freo-1]

mcgsxr,

It's a different ballgame. The Maggie mmg is pretty much a benign four ohm load. Some ESLs get under one ohm, and are capacitive too.

Yep. As a long time owner of Acoustat Spectra 33 speakers, the best amp I found to drive them was Thresholds, with gobs of current and output transistors.  Those puppies would get to 1.1 ohms at certain frequencies. 

[mcgsxr]

Ah, got it.

I know that the Crown amps are 2 ohm stable.  Not sure about 1.1!

[steve f]

I am quite impressed with the ability of some pro amps in home audio use. The Maggies and Crown combination mcgsxr is using should be excellent.

I plan to try a Class H amp with a pair of ESLs in a couple of weeks. This should be a stable drive for my speakers. If it works well, I'll have to deal with things like noisy fans and finding some XLR adaptors for interconnects. Most ready made cords are pretty long; I only need 2 meter lengths maximum.

All I had to add to my  Crowns were stick on rubber feet as their fans are pretty quiet. They have me convinced that the biggest source of distortion in amplifiers is clipping. I'm rethinking what's important in amps these days.

steve

[munosmario]

Best ESL performance I have ever heard is with a pair of Martin Logan Montis  (with their new "24 bit Vojtko DSP Engine" based X-over) driven by a pair of Class D "Cherry Maraschino King" monoblocks, rated at 800 watts/2 ohms.  The Maraschino Kings are totally stable (lab tested) at 1 ohm  and are unflappable driving The Martin Logan’s ES panel load falling to 0.52 ohm at 20 KHz.
 
Incidentally, the Vojtko DSP engine was introduced with the Montis (about 18 months ago) and its responsible for the widely-recognized flawless integration between ES panel and dynamic woofer in the Montis…to such success that it is now used in ML’s new flagship, The Neolith ($80K a pair), which, yes, it is also a hybrid like the Montis (haven’t heard it yet, though, so I have no opinion).

Mario

[steve f]

AAMOF I emailed Tommy about his amps and ESL speakers, and didn't get a reply. I'll ask again on his forum.

[munosmario]

AAMOF I emailed Tommy about his amps and ESL speakers, and didn't get a reply. I'll ask again on his forum.

Steve, for the Montis/Maraschino combination, look in Tommy's Digital Amplifier Company Circle, at reply #18 (from Dec. 8, last year) in the thread about "Maraschino Reviews." Also, look at reply #19 in reference to precisely using Cherry Maraschino amps with Quad ES speakers.

Mario

[JLM]

Just read this from an electrostatic manufacturer's website:

"Some electrostatic speakers have very high capacitance. This raises the potential for three types of undesirable amplifier interaction:

1) All else being equal, the amplifier load from an ESL increases with frequency. High capacitance ESL's will have a very low impedance at high frequencies. When an amplifier that can not drive a low impedance is asked to source a lot of current at high frequencies, the amplifier will limit its output at all frequencies, creating compression, clipping, or some other overload effect.

2) The feedback loops in some amplifiers will not remain stable when driving a large capacitive load. If such an amplifier happens to begin oscillating only when called on to deliver high power, this will cause problems only at high loudness levels. The oscillations may be ultrasonic and thus inaudible, but the indirect, audible effects can include compression, hissing, intermodulation, and chirping, among others. It is also possible to throw an amplifier into an oscillating state called "motorboating", which sounds much like its namesake outboard engine. An amplifier may be harmed while oscillating, or just run warmer than usual.

3) Some switching (e.g., class D) amplifier designs are incompatible with ESL's. If a switching amplifier is designed without enough high frequency feedback, and no special considerations are made in the amplifier for driving ESL's or in the speaker for being driven by switching amplifiers, then the panel capacitance forms a tank with the amplifier's output filter inductance. This will resonate when excited by high frequency signal content, normally at frequencies somewhat but not far above the audio range. It can cause various sorts of distortion, and even arcing of the panels or damage to the amplifier, at sound levels well below the usual limit."

[steve f]

I was told that I should stick with AB or H class amplifiers. Although tubes won't oscillate, most roll off the high end frequencies, so they aren't first choice either.

I did have Crown XLS amps powering a pair of Quad 989 speakers, and didn't notice anything strange. No strange sounds, amp overheating, or protection shutdown happened.

steve

[steve f]

munosmario, Thank you. I read through the thread and the amps are impressive. I'd put them on a short list of amps I'd love to audition. The others being Sanders Magtech, and any Nelson Pass equivalent.

I must admit that I am reluctant to try another D amp just because I've been told it wouldn't work with my new speakers.

[OzarkTom]

Here is a review of the Quad 988 speakers driven by the TBI Millenia amp. This was the early version of the TBI, the latest version is much better, especially using the Astron power supply.

http://www.tnt-audio.com/casse/quad_988_e.html

But driving my Zellaton speakers, I prefer the Crown.