2. amps-preamps
  3. 149865-131497

Will a pair of Manley tube amps be a good match for Martin Logan ESL 11A's?

I have been looking into the Manley power amps to drive a pair of Martin Logan ESL 11 A's. From Manleys specs they report a speaker load of 5 ohms is recommended. The Logans are rated at 4 ohms.
pvmike
bdp24's avatar
bdp24
9,892 posts
 

@georgehifi has given you a good lead in the Music Reference RM-200 Mk.2. It is the only tube power amp I know of that puts out 100 watts at both 8 ohms and 4 ohms (do the McIntosh amps also?). The common wisdom used to be that OTL amps were a great match for ESL’s, and the Futterman amps were often paired with old Quads, single and stacked. Lots of Atma-Sphere amps on Quads and SoundLabs as well.

MR’s Roger Modjeski, a very opinionated designer/builder, disagrees (and has no axe to grind; he builds OTL’s himself). If interested, go to the MR website for more details, and read Michael Fremer’s review of both the original and Mk.2 versions of the amp in Stereophile (and equally important, John Atkinson’s bench test reports).

bdp24's avatar
bdp24
9,892 posts
 
Oops, neglected to include the matter of tube amp output impedance. Many tube amps have a high enough figure to cause considerable roll-off or boost at either the bottom or top (or both) of the audible frequency range when paired with speakers themselves having very low or high impedances at some frequencies, ESLs being exhibit number one. 
mijostyn's avatar
mijostyn
8,570 posts
 
bdp24 and georgehifi are absolutely correct. You may want to read Roger Sanders white papers to get a contrasting view. I personally am not a big fan of using tube amps on ESLs which like jafox I have been running for decades. One transformer is bad enough. Two transformers is really uncomfortable for my brain. Now OTLs get rid of the second transformer and Atma-Sphere amps have a storied history with SoundLabs but I have not heard this combo yet so I can not speak from personal experience. But I have had numerous amps in my system and as a rule Class A SS amps fair the best the two outliers being The JC-1 and strapped AHB2s. I also cross to subwoofers at 125 Hz so the ultimate low bass performance is not an issue for me. You also cross to woofers I think it is somewhere around 250 Hz but don't quote me on that. Biamping would be a consideration but that still does not negate the issue with low impedance at high frequencies. Trick: put a 1 ohm 200 watt resister in series on the + side of the speaker. This will not decrease the efficiency of the speaker all that much and frequently makes the amp more comfortable with the high end. Digikey has them. These are not little devices. They are mounted in 3 inch X 2 inch heat sinks. I always do this if I have trouble with amps overheating and it solves the problem 100% of the time.
bdp24's avatar
bdp24
9,892 posts
 

The following may appear to contradict what I said about Modjeski's opinion of OTL's paired with ESL's: Roger is making his own ESL loudspeaker (which includes an 8" woofer for each side; another pair can be added, of course). But dig this: he is also offering it with a direct-drive OTL amp for extra $. "Direct-drive"? The mono OTL for each speaker has no output transformer, of course, but the ESL has no input transformer. The OTL output tubes drive the ESL panels directly!

Modjeski worked for Harold Beveridge, who had Roger redesign the power amps that were integral to his ESL, also direct-drive. So this is not new to Roger, but it sure is unique. It takes a lot of engineering knowhow to pull off, involving the disciplines of power amps, tubes, transformers, ESL design and construction, and extremely high (lethal) voltages. No kids or pets allowed in the room ;-) .

almarg's avatar
Ag insider logo xs@2x
almarg
9,670 posts
 
The answer could very well depend on which Manley amp is being considered. For example the Manley Neo-Classic 250 has a specified output impedance in the vicinity of 0.5 ohms (John Atkinson’s measurements reported in Stereophile were 0.6 and 0.7 ohms for triode and tetrode mode, respectively). Those are extremely low numbers for a tube amp and suggest that the effects on tonal balance resulting from the interaction of that output impedance and the speaker’s impedance vs. frequency characteristics will be relatively solid state-like. (The RM-200 mentioned by George and bdp24, by the way, has a comparably low output impedance on its lower impedance output taps). On the other hand the Snapper has a specified output impedance of 1.5 ohms, which everything else being equal will result in a less extended upper treble, compared to the Neo-Classic 250.

I have no idea which of those presentations is likely to be preferable with this particular speaker, or how desirable either presentation might be, or how problematical the deviation from the recommended 5 ohm load might be for the amplifier, but as Jafox suggested it would be a good idea to contact the manufacturers and solicit their thoughts about the specific pairing. If you already haven’t, I would also try to find user comments about amplification others have used with the ESL 11A or with its larger brethren in that series (the 13A and 15A). I would not extrapolate much if anything from generalities about ESLs, or from experiences involving other makes of ESLs, as in most cases the Martin Logans are different animals than other ESLs in terms of impedance characteristics, inclusion of powered woofers, and other respects.

Good luck. Regards,
-- Al

More to discover