SS amps with little or NO feedback

Krell and BAT come to mind.

Magfan - Global feedback is OK as long as it is applied properly. The key is to get improvements in THD, IMD and DF but not introduce TIM. It can be done by using shallow feedback just to reduce THD to about 0.1% and then limit bandwidth at the input to one that amp had without feedback. It is always compromise but amp has to be linear and have wide bandwidth to start with. So, I would accept small amount of feedback but would run away from amps with great specifications like THD=0.01%

What "theoretical" problems you have with your class D?

conrad johnson

If you're going to be influenced by topology and advertising slogans, may I also suggest getting a differentially balanced amplifier along with "NNFB". At least that will eliminate the second harmonic and leave you with primarily third harmonic.

Ayre, Threshold.

X2 on Krell amps.

Yeah, there is theoretical problems with everything that only money seems to solve (at least in advertising)! I have also been considering and reading about no-feedback designs(and may start another thread). I am not sure how to conduct a meaningful subjective comparison to more regular SS amps, though, unless I compared a lot of them.

A compromise of those amps to keep in mind is a high output impedance. People like Atma-sphere amps with Magnepan, so it shouldn't be a big deal for you, but the on-paper issue is a voltage drop to the speaker proportionally related by the calculated damping factor. Your speaker, of course is 4.5ohms, which is low but not really low. I am really just suggesting to be aware of that measurement before purchase.

Ayre is another company that advertises no-feedback amps, and Spectron has their ultra-fast control loop which may be interesting to you.

CODA Technologies amplifiers use no global feedback. The company was founded by former employees of Nelson Pass in his Threshold days.

Unsound's suggestion of some of the older Threshold amps may be a good way of obtaining a no global feedback amp at a modest price.

NGJockey makes a good point about the complementary benefits of differentially balanced design, but of course a quality zero feedback fully balanced design will not be inexpensive. Ayre is a good example.

Also, I've seen the Clayton Audio amps, which apparently are outstanding, described as using virtually no feedback. However they are Class A and therefore don't meet the criteria you listed.

Best regards,
-- Al

Al - Fully balanced design has very high CMRR but I wouldn't care about small amount of sweet sounding second harmonic. I would be more concerned with unpleasant odd harmonics created by negative feedback.

How about the Pass X series? Try for the X.5 if you do. They are cheaper ($ for watt) and more powerful than their XA series. They have a nice white paper about the Super Symmetry circuit here.

http://www.passlabs.com/pdfs/articles/susy.pdf

FWIW, I have been using their XA.5 amps for years on my Maggie 3.6's.

Also, the Modwright amplifiers have zero global feedback, and by most if not all accounts are outstanding performers in their price range.

Best regards,
-- Al

Kijanki, if it is a true balanced differential design the main harmonic created will the the 3rd, not the 2nd. All the even orders should cancel. This is true of tube or transistor designs.

Atmasphere - that's what I said. I don't care if sweet sounding second harmonic is canceled (by true balanced amp) while it still might produce unpleasant odd harmonics. Main benefit of true balanced design for me is high common mode rejection - perhaps not worth increased cost.

The "First Watt" amps from Nelson Pass

http://www.firstwatt.com/

Kijanki, I'm a fan of the CMRR too. Makes life a lot easier :)