I have found, generally, that Omegas sound best with single ended class A amps (both solid state and tubes). Not making a blanket statement, just my observation. The F7 is push pull class A (I owned this amp, among about a dozen other Pass & First Watt amps over the last 4-5 years). It's a wonderful amp, but perhaps has too much grip for speakers that are benign loads (like Omegas). My favorites, among Nelson's creations are the F3, J2, XA25, and XA30.8. The F3 and J2 are both single ended class A all the way. With Pass amps, the first few watts (depending on model) are single ended class A, then push pull after that, then slide to class A/B under more extreme conditions. Sorry, didn't mean to derail the thread, but couldn't help joining the conversation regarding the F7.
I will concur with RDavidson in my limited experience. I own Omega speakers in three different configurations, and they all favor a similar type of amplifier: single ended. I’ve used Tripath (upgraded Sonic Impact), PP Class A/B (Redwine Audio), SET/SEP (Dennis Had and Oliver Sayes), and SS SE (DIY FIrstwatt). Power has ranged from 4wpc to 32wpc. With all speakers, I had more power than I needed.
In order of sound preference in my system:
1. Dennis Had Inspire PSE amp. This is a little unfair, since this is a pretty special piece of gear. This is a parallel SEP amp that will run just about any Pentode or Beam Power tube you can fit into (or adapt to) the sockets, plug and play. The amp has tremendous grip in the bass without sacrificing SE magic. It is also very tunable by swapping output tubes. Right now I am rotating sets of 6F6 (10wpc) and KT77 (20wpc) tubes.
2. Oliver Sayes 421A SET. Again, this isn’t really fair since this is a custom build of Don Garber’s 421A circuit by a talented custom builder with a great ear. This amp puts out 4.5wpc and with an input sensitivity of 0.65V it can be run directly from just about any source. It has an Alps pot and single input and vintage Jensen PIO coupling caps.
3. DIYAudio/Nelson Pass Amp Camp Amp (kit). This one is a no-brainer. This kit sells out almost immediately when it becomes available and is very easy to build. It is a SE MOSFET stereo amp that outputs 8wpc with the 24V PS. This amp gives an insight into the more expensive Pass/Firstwatt offerings and is better than most amps on the Omega’s. A great “entry level” system is a Amp Camp Amp ($325), Chord Mojo ($579) and Omega Super # Monitors ($695).
4. Tripath Amp. This is the slight more upscale Sonic Impact Deluxe from Parts Express. It’s still a cheap ($50) amp that sound surprisingly good. I haven’t put in any effort to improving this amp, though it responds well to reasonable upgrades (mostly PS). It was a little tizzy with my Omega Super 3’s when they had the Foster drivers, but actually sounds good with the RS5 drivers.
4. Class A/B Amp. Redwine Audio Signature 16. This is a beautifully built amp that sounds great, just mot with Omega speakers. It is battery powered, tube-buffered, with a class A/B amp putting out 16wpc into 8 ohms or 32wpc into 4 ohms. This amp had the worst match with my Super 3 HO monitors. I think the slightly lower impedance in the bass range actually gave me too much midbass power. I think the rising impedance of single drivers is also not well-suited to this amp, producing a rolled off top end. I do think this amp would sound good with my Yamaha NS-690’s, but at this point in life I am running out of time and space to test different configurations.
Other thoughts: I also own a DIY Firstwatt F3 “kit” that remains unassembled. It is a bit more daunting than the Amp Camp kit, since it comprises USA boards and parts. This is alleged to be one of the best sounding of the Firstwatt amps within its power limitations. Others seem to gravitate to the J2 for Omega’s. I would imagine the SIT series might be the best of the lot for these speakers.