I've been fortunate enough to have the pair that Bill sent out for RMAF in my system for the past two weeks and while I'm certainly not a reviewer I can say that I really like these amps. My system is actively bi-amplified so the M156's are running from 275Hz up so I can't comment on their bass but the mid and high frequency clarity is excellent with full extension and no high frequency roll off.
These amps encourage tube rolling as well. They arrived with the factory tubes, which give a very clean and somewhat lean presentation, at least for my taste. From what I've read and been told they can get all the way to syrupy depending on tubes. Well I prefer syrup on my pancakes and not in my audio system but I did want a little more richness. I happened to have a pair of NOS RCA 12AU7's I picked up some years ago that I never found the right home for. I put these in the first position of the M156's and I have now found the right place for them. With the RCA's on the input (I'm guessing as I don't have a schematic and I'm certainly not going to open them up) the M156's became just right for my tastes and system. Still clean and extended but with a bit more harmonic richness and body.
My main amp is a 100W custom OTL which also doubles as a space heater with 20 6AS7G output tubes. While the OTL is a bit more transparent, the EE amps are very close and have considerably more power and provide somewhat greater dynamics even though I rarely hit more than about 20W of output. My speakers are Meadowlark Blue Heron II's that have been modified for use with an active crossover. They have a sensitivity of 91.5dB (measured) so they will play very loud with only a few watts.
Speaking of measured, in order to incorporate the amps into my system I needed to know the gain. The manual specifies this as 30dB but I decided to measure it to sure. It was exactly as stated. While I had it on the bench I took some frequency response and THD measurements as well. The amp beat all the published specs without a problem. I didn't measure the maximum power output as I don't want to risk cooking a tube in something that isn't mine but I did measure it at 1W and 12.5W of output at various frequencies and it was very well behaved.
Kudos to Bill O'Connell for putting accurate specs in the owners manual and for including the gain, something too many manufactures don't do. While basic measurements don't come close to conveying how the amp will sound, it's nice to know it measures as good as it sounds.
For the last week I've been spinning vinyl and the M156 amps are really letting the delicious sound of a good record out. They have just gotten out of the way and let the music flow, about the highest compliment one can pay a piece of gear. The system is flat out addictive with vinyl and the M156's.
One gentleman I know said that in his system the amps were the the star of the show, this is certainly not true in mine, they just seem to do their job with no fuss and without drawing attention to themselves. Like anything else you have to hear them in your system. Tube amps, even big power houses like these, are more sensitive to the impedance and phase swings of the loudspeaker so what works for one may not be a good match with another. If you can get an audition take advantage of the opportunity.
I'm going to miss these when they are gone. One of those times when I wish my wallet were fatter.
mike g
