What are some amps you’ve heard with high feedback that you’ve enjoyed? I’ll have to check them out. I’ve seen the measurements for the Purifi and its distortion is incredibly low, to the point it’s at the limits of what the AP analyzer can measure. It does have raising distortion in the treble but if I had to surmise, it is most likely low order as I find the purifi a touch sweet in the treble. I do run it without an input buffer as my preamp is up to the task of driving the Purifi module directly.
I have yet to hear the new Gan stuff that is specifically designed for audio. I know yourself and AGD specifically designed yours for audio applications unlike many of the other brands. Are you guys going to be at the pacific audio fest? I’d love to come hear your Class D amps and hear how it compares to the 300b statement monos.
Our amp of course, which you have to imagine we’ve compared extensively to our class A triode zero feedback OTLs.
The AGD Audion (although I don’t know how much feedback is employed in this design)
Orchard Audio
Digital Amplifier Company (unfortunately the designer passed away last year)
We won’t be at the Pacific Audio Show- I have a prior booking.
Interestingly, Class D amps are free of Class AB transition artifacts, so there’s an entire class of coloration that just isn’t there. The big issue for Class D is nanosecond precision of timing for the pulse-width modulation (Class D is pulse-width-modulation, akin to FM, and not PCM), and insensitivity to reactive loads affecting the PWM modulator.
Yes, crossover distortion artifacts are impossible for any class D using an output filter. Timing issues (which cause an unpleasant hiss) are solved by a self-oscillating topology. This is done by exceeding the phase margin of the amp and the oscillation is used as the switching frequency. This makes for a very high stability amplifier and very large amounts of feedback. Since the feedback is not distorted prior to doing its job, higher ordered harmonic generation is avoided. Essentially the feedback simply reduces the existing distortion (in our circuit this tends to be lower ordered harmonics). Distortion vs frequency winds up being a flat line across the audio band. So it sounds very much like a zero feedback triode amplifier, but more ’focused’ owing to lower distortion, which otherwise obscures detail. You should try it- you make excellent amplifiers and know how they are supposed to sound, so you are in a good position to see how this technology advances the art.