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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
georgehifi's avatar
georgehifi
10,312 posts
 

An amp like say a Krell or similar, will remain almost flat in it's response across the frequency spectrum.
All you need to do is look at the simulated speaker load graphs of amps at 1/3 power on Stereophile to see what happens to them if they have, high'ish output impedance or can't deliver current, many tube amps exhibit this, and even many Mosfets, they are far from the ideal flat.
And the simulated speaker load that Stereophile uses is not as savage as what we're talking about here with the ML's, and things like Wilson Watt/puppy, Alexandria etc.

Cheers George
georgehifi's avatar
georgehifi
10,312 posts
 

Here is an Audio Research Reference 150 considered by many to be a tube amp with better drive than most.

It's only being asked to drive 2.83v hardly taxing.
Look at the black trace in the link, this is Sterophile's simulated (rather easy speaker load), the 150 is having a hard time staying flat.(I can show you an impedance graph of their simulated speaker load, I have it somewhere it's not as nasty as the ML's)

Then look what happens to it when it has to drive a straight 2ohm load (green trace) it's really starting to take a dive in the upper mids/highs. What do you think will happen to the highs into a 1ohm capacitive load of the ML's

http://www.stereophile.com/content/audio-research-reference-150-power-amplifier-measurements#dgk5iym3Akuwqg5H.97

Cheers George
georgehifi's avatar
georgehifi
10,312 posts
 


Here is a link to those Stereophile simulated speaker loads, as I said hardly as taxing as the ML's loads.

http://www.stereophile.com/content/real-life-measurements-page-2#GhGr6lrCxHfPYcsl.97

Cheers George
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almarg
9,670 posts
 
Again, though, as I indicated in my previous post George's comments mainly address frequency response at the amplifier output/speaker input. And flat frequency response at those points does not necessarily mean that the acoustic output of the speaker will have flat frequency response.

Ralph (Atmasphere) stated above that "in an ESL, the efficiency is fairly constant despite the impedance." ("Efficiency" referring to acoustic power out vs. electrical power in). I believe that is generally true. But even if we assume that the efficiency of a given ESL is just a little bit closer to being constant across the frequency range than it is to mirroring the impedance curve, then the minimal variation of amplifier output voltage as a function of load impedance that is characteristic of almost all solid state amps (assuming they are operated within the limits of their voltage, current, power, and thermal capabilities), and hence the increase in power delivery that will occur as impedance decreases, will result in greater frequency response variation in the acoustic output of that ESL than would result with a tube amplifier (operated within its capabilities) whose output impedance is some relatively high value, and whose output voltage therefore varies significantly as a function of varying load impedance.

Apologies for the long sentence :-)

Regards,
-- Al
georgehifi's avatar
georgehifi
10,312 posts
 

Yes Al and that why I say a Quad 57 is voiced around a low power low current tube amp, but with Martin Logan's statement:
"Quote:
However, it is important that the amplifier be stable operating into varying impedance loads: an ideally stable amplifier will typically be able to deliver nearly twice its rated 8 Ohm wattage into 4 Ohms, and should again increase into 2 Ohms." Quote:

This is why my ML Monoliths have very subdued/rolled off character in the uppermid/highs and dynamics when driven from my tube Rogue 120 monoblocks.
Yet they sound perfect and well extended when driven by my big current pushing solid state monoblock amps.


Cheers George
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