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Using tube amp with electrostatic speakers.

Moons ago I started similar discussions and thought I had been given enough good advice not to approach the subject again. Here goes anyway. I've used Martin Logan electrostats for well over 30 years with quite a few different amps but have recently switched to a tube amp and dynamic speakers with which I am very satisfied.  It consists of the Cary Rocket 88R amp and Serie Reference 3 speakers. 

My brother was visiting last week and was so impressed with the sound that he decided that he might want to try a tube amp also (probably the same one as mine).  However, he is using a pair of SL3's that I gave him years ago and I'm concerned primarily about the current requirements of the Martin Logans as well as other concerns that I'm not thinking of.  I don't want him spending money on something that may not bring him improved sound so would appreciate more advice to pass on to him.  He currently uses a Rogue Audio SS amp with his SL3 speakers and, to me, it sounds very good. 
jimbreit
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almarg
9,670 posts
 
Great post, Lew.  Thanks!

The only thing I would add is in connection with this statement near the end:
... it is my opinion that so long as the impedance remains reasonable at least up to 10kHz, the low Z above that frequency is nothing to worry about; there is very little energy demand on the amplifier for frequencies above 10kHz...
The low energy demands in the top octave will of course work to the amp's advantage, as you indicated.  I would add, though, that there can still be effects in that region on tonal balance and in how accurately high speed transients are reproduced that will vary as a function of the relation between amplifier output impedance and the speaker's impedance characteristics in that octave.  Those effects will become increasingly pronounced as speaker impedance in that octave decreases relative to amplifier output impedance, everything else being equal.  Although as you indicated the specific relation between those characteristics that will be sonically optimal very much depends on the particular speaker and the particular amplifier.

Best regards,
-- Al
 
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bdp24
9,820 posts
 

From my reading, I am aware of another consideration in these matters. The way an amplifier circuit reacts to very high frequencies presented to it, frequencies too high to be heard on their own, can affect the behavior and sound of the amp. A barely-stable circuit can be driven into oscillation by those frequencies, creating ringing and different forms of distortion.

Frank Van Alstine and Roger Modjeski have discussed this area of amplifier design in their writings, and it is an important consideration with ESL loudspeakers. They benefit greatly from an "unconditionally" stable amplifier. Both Frank and Roger make such amplifiers, though they are not alone in doing so.

lewm
13,110 posts
 
I think Al and I did allude to such issues.  It is not the high frequency information per se, unless you are talking about RF, which is never good for any system, but how the load (the speaker) reacts to those frequencies in a way that then feeds back on the amplifier.  Traditional SS amplifiers that use a lot of Negative FeedBack (NFB) tend to be driven into oscillation by the capacitative nature of an ESL as load.  Any modern design worth its salt should be Ok in this regard, probably including those made by FVA and RM, two of the oldest old timers in the business. (No disrespect intended; I suddenly find that I am an old-timer too.)

By the way, for most adult males beyond the age of 35 or so (which is almost certainly all of us here), even 14kHz is well beyond audible. Yet, I perceive that wide bandwidth is a "good thing" in electronics.
stewart0722
184 posts
 
Planars whether it be magnetic or electrostatic sound their best when fed prodigious solid state juice.....

I have Magnepan 3.7s and I use Bryston 28BSST2's

I do couple it with a full tube pre (Convergent SL1 Renaissance)

I don't think I give anything up to a full tube rig in terms of overall
musicality, but I gain a lot in terms of headroom.....
bdp24's avatar
bdp24
9,820 posts
 

Good info Lew. Yup, 14k is inaudible to me too now, thanks to over fifty years of performing and attending live shows, some with excruciatingly loud SPL. I had molded ear plugs made when I was in my 30’s, but the damage had been done. Youngins’, don’t put it off, use protection!

Stewart, ESL's and Magnetic-Planar loudspeakers present quite different loads to an amp, ESL's a very reactive one, M-P's a resistive. In addition, ESL's benefit from a voltage source type amp, M-P's a current source design. That's why Roger Sanders makes an amp for each type loudspeaker. Right Lew? 

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