Hello Gary,
I just recently signed on and came across your inquiry of these mono amps. Not much of an audiophile but hope I can share a little. Designated OM90.1A These mono amps were introduced by Mark Shifter, the previous principle of Audio Alchemy. Briefly, these amps spec’ed out as follows.
Power Output
8 ohms —- 90 watts RMS Class A
4 ohms —- 160 watts RMS Class A
2 ohms —- 250 watts RMS Class AB
1 ohm —- 400 watts RMS Class AB
Bandwidth
Small Signal —- 2.83v into 8 ohms, -3dB 0.4Hz and 350KHz
Gain —- 28.6 dB
InputBalanced —- 200 Kohm with XLR
Unballanced —- 100 Kohm with RCA
Power Consumption
120v AC idle at 500 watts, peak power 800 watts per mono.
Weight —- 85 lbs.
Retail Price $10,000 per pair
I happened to know Mark through my hobby in the 90’s. After his first visit to my home, he learn that I was chasing after the world of Tube. After some brief discussions, he asked me to give his new baby a listen. So I took delivery of my OM pair late 1996 directly from the factory. They were rushed to me just off the QC line. So rushed in fact that there weren’t any serial numbers. I liked enough of what I heard that I purchased my second pair 3 months later. Upon arrival, the power switches of these were through round holes instead of rectangular. So Mark arranged for me to return them and send me #900513 & #900514. I have 2 pairs.
Unfortunately, my pre-occupation with tubes didn’t allow me to use these OM’s as much as I should have. I don’t really think they were properly broken-in to this date. With one pair driving my ribbon panels, they sounded somewhat sweet and a bit like my VTL’s. Unfortunately, one pair didn’t provide enough drive to move my ribbons like the VTL’s. The currents from these 750 watt monsters drives with suave dynamics. So at Mark’s recommendation, two pairs of OM’s were employed ala mono-bi-amp. Then the speakers opened up.
I had the OM’s rotating in and out of my system for over a year. There was only one failure. One amp failed driving my tweeter array. After speaking to the designer, Andy, over the phone, we traced it down to weak or faulty rectifiers. I found a stronger substitute NTE 5340 to replace the original RU CM3602. Apparently, these amps draws tremendous amount of power during startup and may overwhelm the rects. Later, I heard that there is an even better substitute, EDI BRUS4 ultra high speed bridge rectifiers. Haven’t had the chance to try them yet.
Due to the constant current draw, 500 watts at idle, these amps runs very hot. Almost too hot to leave my hands on the cage for extended period of time. Heat is the enemy of all things electronics. I recommend removing the inner plates covering the central capacitor bank but keeping the external chassis on. I also raised these amps on aftermarket cones to provide more ventilation. The tubby rubber feet is insufficient. (I prefer my original steel tip-toes over the Black Diamond Racing #3) Doing so showed a meaningful temperature drop as measured via my Tenma probe. And please keep them off carpets.
I’d heard someone claim them to be the best Class A amp a few years ago until the arrival of his Pass XA100.8 monos. Well, haven’t tried those in my system. But this is so system and person preference dependent. Perhaps I should give my quad-OM’s another listen. It’s been almost 20yrs since they’re last used.
Hope you find this useful.
Paul
PS: I also a report that these amps shouldn’t be power up with no speaker hooked up.
