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OTL Tube Amps and Full Range Electrostatic Speakers

I have Martin Logan CLX speakers which have a nasty impedance curve in the treble with a minimum of 0.7 ohms at  about 18 to 20 kHz - or so I have read.  The impedance of the CLX is, as many know, largely capacitive.  Over the years I have preferred tube amps and have heard OTL amps driving various Quad speakers with great results.  My own experience with the CLX's has been more positive with high quality solid state amps; I am currently using a Krell 402e which has no trouble driving this speaker well.  An ARC Ref 150 did not provide the control, particularly in the treble, which this speaker needs and did not provide the level of transparency which this speaker can provide.  I would appreciate hearing if anyone has experience with other tube amps with the CLX's or Sound Labs, particularly OTL's and whether autoformers provided a significant benefit.  Thanks for any insights.
soundhound

Showing 1 response by clio09

clio09
3,372 posts
 
We have a number of customers using the RM-200 with their ML speakers. It's an excellent amp for the job. OTLs can also sound great, if Atma-Sphere I would recommend the MA-1 which is 100 watts. I'd recommend putting the autoformer in between the amp and speaker, but it may not be necessary. Ralph could advise as well.

There is some debate on whether the Berning patent for his design and that is now used in the LTA amps is actually an OTL circuit. IIRC there is a high frequency transformer that follows the tubes in the circuit. Therefore, some feel that technically it can't be an OTL and I believe Berning more accurately refers to the design as Zero hysteresis since that high frequency transformer does not behave like a traditional output transformer. So the other side of the argument is if it doesn't behave as an output transformer it is still an OTL (output transformer less).
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