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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
atmasphere's avatar
atmasphere
11,807 posts
 
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.

'Stable' means that the amp won't oscillate when presented with the load in question.

Atmasphere, perhaps I'm not seeing the same things you are?

Perhaps. Take a look at Fig 4 at the link you provided.
georgehifi's avatar
georgehifi
10,312 posts
 
04-11-14: Atmasphere'Stable' means that the amp won't oscillate when presented with the load in question.
Stable is a given with any amp, you may have missed the rest of the Martin Logan quote for the type of amp they recommend for their speakers. And to get these sort of figures, the amps need low output impedance, to get it. So here it is again.

" Be able to deliver NEARLY twice its rated 8 Ohm wattage into 4 Ohms, and should again increase into 2 Ohms."

In other words for the uninitiated, what's needed is an amp that can ALMOST double it's 8ohm wattage for each halving of load.

EG:
8ohm-100watts
4ohm-200watts
2ohm-400watts

Cheers George
jafox
1,456 posts
 
If you want a tube amplifier to mate with ELS speakers, that excels effortlessly and with outright awesome dynamic contrasts, very low level resolution, go the the CAT and never look back.
labtec
189 posts
 
Funny to read this thread about autoformers.

Probably 6-7 years ago, I added a McIntosh SS amp to my arsenal that uses autoformers. At the time, I was also using Steve McCormack's platinum modded amps too. I compared them and shared my thoughts with Steve about the improvements possible with adding an autoformer as an additional mod for his amps and suggested the Paul Speltz product.

He noticed the same thing and, apparently, even wrote about it. I've been inactive in this hobby for quite some time, so it's fascinating to see this recent discussion of something I was dealing with when I last was “involved" in the hobby.

I echo everything Atmasphere is saying and can vouch first hand...not because I was prejudiced or persuaded by forums or audiophile "authority"...but because I discovered this phenomenon organically...almost by accident.
hvowell
13 posts
 
This is all well beyond my understanding and wondering can someone comment on a question concerning the voltage vs power model? I believe I read two, perhaps more, points of view?

Concerning an ESL such as the Quad "57" referenced earlier with a SS amp "doubling" the amps output as the impedance is halved (assume)

25W into 8ohms
50W into 4ohms
100W into 2ohms

would not the output be also "halved" as the impedance rises above 8ohms

12.5W into 16ohms
6.25W into 32ohms

If I understand correctly than, for the Quad ESL this means only 6.25W/12.5W in the lower frequencies while 100W into the higher frequencies?

Now is the reason this type of amp works is (assuming the speaker has a sensitivity (SPL) of 85db/1W into 8 ohms)

.25W into 32ohms = 85db
.50W into 16ohms = 85db
1W inot 8 ohms = 85db
2W into 4 ohms = 85db
4W into 2 ohms = 85db

so the SPL remains constant into all impedances?

Thank you everyone for all the previous information, so very informative!

Lee

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