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Pass makes a good case for ZERO negative feedback ...

... but a poor case, (or no case at all), for low to moderate feedback.

Referring to the aforementioned graph, (below), note that higher order harmonics enter the picture progressively, 6th at about 15 db, and presumably higher mostly by 20 dB. Thereafter all orders decline. Intermodular distortion is, of course, related to the levels of harmonic distortion. Sorry, but I can't help suspecting that there is some level at which distortion becomes inaudible.

?

So his following graph looks UGLY but note that the highest feedback is 15 dB -- just about the the peak for 6th order distortion per the preceding graph! And even in this here the 4th, 5th, and 6th seem to peak at 10 dB.

?

Pass avoids the logical conclusion that higher feedback might work better than low or moderate feedback. Pass does suggest that a lot of feedback might require additional amplification stages but doesn't deal with the likely positive effect of global feedback vs. local.

As for space/soundstaging, transparency, and resolution, my own (albeit limited) experience is that my Class D amps are better any Class AB amps I've owned, including the high-bias, low feedback Monarchy SM-70 Pro.

BTW, I'm not privileged to listen to really high-end equipment in my system, much less own it. So I have to work out what's best for me in cheap equipment. And for me resolution, transparency, and accurate instrument timbres trump warmth, "harmonic richness", and the echoy false ambience you get with cheap (or not so cheap) tube equipment.




Dmitri Shostakovich


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