Please Read and express your feelings and opinions....

"Can't we all just get along?"  

Anonymity in cyberspace is the breeding ground for all sorts of bad behavior including bullying and brow-beating.  Some forums and forum moderators run a tight ship; others not so much.  Methinks the governing thought is that we are all adults and should behave accordingly.  That doesn't seem to work out so well does it?  As someone mentioned, it is the nature of the beast.

Whether it is high-end audio, sports, hobbies, automobiles or your favorite food, everyone is entitled to their opinion - but one must understand and recognize that it is "their opinion" --whether it is based in fact or not.   We come from different cultural and educational backgrounds.  We all have something positive and constructive to contribute.  

Maybe a few ground rules are in order (as long as they are observed and enforced):

It's important to remain civil and respectful.  Agree to disagree.

Think before responding

Stay on point

Attack the problem - not the person

Educate not intimidate

Share. Enlighten. Have an open mind. But most of all, have fun.

I assume the discussion is concerning global negative feedback and not local feedback. My amps as well as several other major brands of tube amps use negative global feedback. VAC, one of my favorite major brands, states that their amps use 6 db of negative global feedback. The finest audio/music system I’ve heard is the VAC/Von Schweikert $1million system.  I suppose Kevin could have built the amps with no or less feedback, but his design works great with it.

My amps have four variable points of negative feedback which I use the minimum for most recordings (some bad rock CDs need more feedback to make them listenable for my wife). I’ve tried no feedback amps and am dissatisfied with their sound (they were also Class A type).

Negative feedback is certainly a subject that generated plenty of heated debate. The one thing I don't think anyone can argue about is the importance of optimizing the topoly to behave decently before attempting to correct it's bad behavior. I think that's where the solid state crowd can learn from the tube crowd. Tube guys are obsessed with tuning a circuit to get good behavior from the gain devices because gain in their world is too scarce and too expensive to be throwing away on gobs of feedback. 

To add a data point to Steve’s (Fleschler’s) input, my 300B-based class A biased VAC Renaissance 70/70 MkIII amplifier provides a choice of 6 different feedback settings, ranging from 0 (no feedback) to 7.5 db. All of those choices represent relatively modest amounts of feedback, even for a tube amp (for example ARC amps commonly have feedback in the area of 10 to 14 db or so), but nevertheless I prefer the 0 db setting. I suspect one reason for that is that my speakers (Daedalus Ulysses) have an exceptionally flat impedance curve. Presumably that tends to lessen their sensitivity to differences in amplifier output impedance, which in turn will vary among the different feedback settings, and will be highest at the 0 db setting. I’d imagine that with a lot of other speakers one of the other feedback choices would be preferable, depending on how the impedance of the speaker varies over the frequency range, and also on how much bass damping it requires (damping factor being inversely proportional to output impedance).

Regards,
-- Al

Thanks Al, I didn't know that older VAC amps have variable feedback.  

My 125 watt Class A/B tube amps also have variable global negative feedback at reportedly 4,6,8 and 10 db.  My similarly high efficiency speakers, unlike yours, have a difficult impedance curve with low impedance in the bass (3.2 ohms).  I set my feedback to 4 db, or minimum.  Until I improved my system with the SR fuses and Total Contact, I used to set it to 6 db for CDs and 4 db for LPs and 78s.  Now everything sounds open and tonally firm at 4 db.  

If I were to replace my amps, I would probably buy the VAC 200IQ.