Tube Amp for Martin Logan Speakers

I was just giving you guys a hard time. That doesn't come through in print very well. We get too serious sometimes.

Of course not every amp can handle the job when you've got a speaker that has an impedance of .5 ohms at 20khz. But you don't need a lot of power to reproduce most musical content at 20khz either. The highest fundamental on a guitar is less than 1khz. Overtones are very important but don't need a lot of power to reproduce.

Robert Deutsch had no problem with the 40wpc Prologue Premium Integrated and the ML Montis.

Here is what Martin Logan says in the manual for their current hybrids:

What size amplifier should I use?

We recommend an amplifier with 100 to 200 watts
per channel for most applications. Probably less would
be adequate for our smaller hybrids or when used in
home theater where a subwoofer is employed. Our
hybrid designs will perform well with either a tube or
transistorized amplifier, and will reveal the sonic character of either type. 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 wattage into 4 Ohms
and should again increase into 2 Ohms.

And:

Could you suggest a list of suitable electronics and
cables that would be ideal for Martin Logan speakers?

The area of electronics and cable choice is probably
the most common type of question that we receive. It
is also the most subjective. We have repeatedly found
that brands that work well in one setup will drive
someone else nuts in another. We use many brands
with great success. Again, we have no favorites; we
use electronics and cables quite interchangeably. We
would suggest listening to a number of brands—and
above all else— trust your ears. Dealers are always the
best source for information when purchasing additional
audio equipment.

So, you don't want an SET but you shouldn't be too worried about that .5 impedance either. ML did not say the amp has to double wpc with each halving of impedance, not even close. I do not think that a company that has lasted as long as ML has in the high-end world could get away with advising customers to use amps that make their speakers sound bad.

So, We need to be aware of specs but Trust your ears and Enjoy your music!

Tom, you quote the ML manual as advising that "an ideally stable amplifier will typically be able to deliver nearly twice its rated wattage into 4 Ohms and should again increase into 2 Ohms."

My take-a-way is that ML recommends using a rock-solid stable SS/Voltage Paradigm amp, which as discussed above has a very low output impedance. Stated differently, the ML ESLs in question were likely voiced to be driven by a SS amp.

Hence, based on what Al explained, using a tube amp which has a "high'ish" output impedance will likely result in sonic coloration to some degree. As Al also said, some may not find this to be a problem and that's ok. :)

So ... after all that has been written, I think the best answer to the OP's Q is that if he/she really wants to use a tube amp to drive his/her ML ESLs, consider a low output impedance BEAST that can deliver serious current.

Frankly, I would be biased (pun) in favor of using a high quality/high power SS amp e.g., a Pass, Ayre, Bryston, inter alia.

Regards,

Bruce

03-31-14: Tomcy6
Of course not every amp can handle the job when you've got a speaker that has an impedance of .5 ohms at 20khz. But you don't need a lot of power to reproduce most musical content at 20khz either.

True, but if the amp cannot keep constant voltage at 20khz it will result in the treble being shelved down no matter what volume level you are listening to, resulting in a softened treble, some unexperienced might call this smoother, but their having themselves on.

(as the sterophile test reports state)
Quote Sterophile: " The shape of the impedance trace will result in the Montis's top octaves shelving down when the speaker is driven by a tube amplifier having a high source impedance. This is why Robert Deutsch found that his Audiopax amplifier sounded too soft and lacking in definition."

Cheers George

"Hence, based on what Al explained, using a tube amp which has a "high'ish" output impedance will likely result in sonic coloration to some degree."

Yep. The specs give you guidelines but cannot answer what sounds best in each case. The key part is "to some degree". The question is always which colorations and to what degree. The answer will be different likely in each persons case though the specs might indicate certain approaches to yield the best results overall.

Its funny how there are always two ways to look at good sound.

1) technical
2) practical/case by case

Nothing guarantees each perspective will resulting the same choices/solution. Why should they each case is different even if for no other reason than room acoustics and how each person hears. Would we expect two people to choose the exact same pair of shoes? No. But we all kinda know what makes some shoes better than others. That's the technical perspective and the only one of global value. But then , the shoe gotta fit....