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Tube Amp for Martin Logan Speakers

Hi, I love tube sound through my Martin Logan Aerius-i fronts and Cinema-i center. I currently have a Butler 5150 which is a hybrid, but it busted on me and would cost $700 to fix. I've had china stereo tube amps that were pretty good and gave true tube sound, but not enough drive for higher volumes. I live in condo, so not like I can blast music anyways but still. I got the Butler because I wanted 5 channel tube sound for home theatre (The piercing sound from my Denon 3801 receiver was not pleasant to my ears). It appears there are only three multi-channel tube amps around, from Mcintosh, Butler 5150, and Dared DV-6C. The latter two are hybrids, and the last one was one of the worst tube amps i've ever heard. I have no clue why 6Moons gave the Dared a 2010 award, but maybe it's because it produces only 65W.

So since multichannel tube amps are hard to come by, and they tend to be hybrid, I was thinking maybe it would be best to get three true tube monoblocks to power my fronts. Thing is I wonder if they will be underpowered for my speakers, and not sure which ones are decent for the price. Maybe China made ones would suffice, and they still go for pretty expensive price. I'm wondering if anybody knows of a decent powerful tube monoblock that is affordable, because I can't pay $3000 per block. or maybe best to just repair my Butler. Thing is, I'm not confident that it is reliable. The tubes are soldered in which is weird, and i've taken it to a couple repair guys who both said that the design is not good, because it's very tight inside and more susceptible to being fried from DC voltage areas. it's too sensitive.

Any suggestions for tube monoblocks, even if china made ones? the holy grail for me would be Mcintosh tube amp, but they are hard to come by. Thanks.

smurfmand70
bifwynne
2,206 posts
 
Thanks Al .... that's exactly what I surmised the directionality of the impact might be. Btw, if ZEROs are used to double the ML's apparent impedance plot, would that change your calculations?? And your comment about whether any amp, SS or tube, can drive the MLs within its respective SOA (see EPDR article) is a whole "nuther" kettle of fish.

Btw, did the ML's phase angle plots factor into your calculation? If so, directionally, how so (if phase angle is negative or positve)? I intuit that harsh phase angles can constrict the SOA of an amp (SS or tube). I am not clear of the impact on sonic coloration, assuming the amp is operating within its respective SOA.

Incidentally, to my sorry old ears, I find a sonic coloration of even 1.6 db to be noticeable. I base that assertion on my amp/speaker combo.

Based on John Atkison's review of my amp, he reported that the output impedance off the 8 ohm taps is about 1'ish ohms, resulting in output voltage regulation variation of +/- .8 db (ergo a theoretical spread of 1.6 db). By contrast, those figures are roughly halved off the 4 ohm taps.

In practice, I find that my speakers sound less forward and have deeper, more extended bass when driven off the 4 ohm taps. That is consistent with the impedance plot of my S8s, which have roughly a 20 ohm peak at 2K Hz (x-over point) as compared to a 4 ohm saddle in the "power range" of 60 to 500 Hz).

Thanks again Al. You manage to lift the veil of confusion for non-techs folks like me.

Regards,

Bruce
tomcy6's avatar
tomcy6
2,589 posts
 
Someone should tell Martin Logan about all this. Those idiots are telling people that their speakers can be used with a wide variety of tube and solid state amps.
unsound
7,329 posts
 
^Yes, someone should do it immediately, as they might be inadvertently garnering more sales.;-)
georgehifi's avatar
georgehifi
10,312 posts
 
03-30-14: Tomcy6
Someone should tell Martin Logan about all this. Those idiots are telling people that their speakers can be used with a wide variety of tube and solid state amps.

Some tubes can drive them without becomming too much of a "fixed tone control" (ie: not flat from 20hz to 20khz), but they need low output impedance to do it, below say 1ohm from 20hz-20khz) like ones I metioned earier, which usually have a fare amount of negative feedback on them to keep them below 1ohm output impedance.
They also need to back it up with a bit of watts also.

Cheers George
bifwynne
2,206 posts
 
That's right George. My ARC Ref 150 might (???) be able to handle the current demands because it has a beefed up power supply -- 1040 joules. And, as I mentioned above, the output impedance off the 4 ohm taps is roughly .5 or so ohms. As a result, my amp performs somewhat like a solid state amp.

Hopefully, Al will come back with a response to my follow up questions: (1) whether ZEROs will change his calculations; and (2) how does the phase angle spec at a particular frequency affect his calcs.

That folks is why I persisted with my comments. I can't do the math, but after 2 or 3 years of this back and forth with Al, Ralph and some of our other tech members, I better appreciate the challenge of matching amps and speakers. Also, when I see that a speaker's impedance plot is literally off the chart, e.g., the ML ESLs and some of the B&Ws, I raise an eyebrow.

So ... this goes back to what Ralph (Atmasphere) said all along. Optimally, if a speaker manufacturer could design a speaker with a flat impedance plot, say between 8 and 16 ohms, with a zero phase angle across the frequency spectrum, the SPCA would go out of business.

And once again, the SPCA stands for the Society for the Prevention of Cruelty to Amplifiers. :)

Cheers,

Bruce
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