Music Reference RM200 mkII. Power increases into lower impedances!
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.
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Exactly roberjerman, and the RM-200’s low output impedance is a bonus with the impedance swing many ESL’s present to an amp. It is also very stable into highly-capacitive load of most (all?) ESL's. A mighty fine amp, made specifically for difficult-to-drive loudspeakers. Roger is now making a direct-drive OTL amp, specifically for ESL speakers, including his own. About $6,000/pr, I believe. Check the Music Reference website to confirm. |
Thanks to roberjerman, bdp24 and kalali for their comments. I have heard the Futtermans on Quad 57's and it was a great combination. I have used a number of highly modified ARC tube amps on Quad 63's, 989's, and 2805's with good results. I have had a number of Sound Labs - most recently the A3's - as well as many Martin Logan hybrids the CLS IIZ and most recently the CLX's. While it is probably not worth delineating all the amps - both solid state and tube, Pass, Rowland, Levinson, Krell, ARC, CJ - that I have used over the years with these speakers - I have not used OTL's with the ML or Sound Lab speakers. There have been a number of OTL manufacturers over the years, but currently I am aware of only Ralph Karsten at Atma-Sphrere and Roger Modjeski at Music Reference who are currently producing OTL amps. The CLX is perhaps the most fussy speaker that I have had both in setup, room requirement for optimal performance and the upstream equipment needed to optimize its performance. I suspect that is why one sees CLX's on the used market. Has anyone had personal experience with OTL's on either the ML CLX's or the larger full range Sound Labs? |
Some more OTLs that have been popular recently... (I haven't heard them) https://www.lineartubeaudio.com/new-page-1/ |
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