Why do audiophiles shun feedback in amplifiers?

Ralph I think we're confusing semantics regarding 'tight' bass. To me, a KT88 amp with feedback has more natural bass than most SET amp with no feedback or for that matter an OTL amp with miss matched speakers.

Thanks everyone for the informative responses. In regards, to speaker/amp pairing, I have three sets of speakers, two pairs are dynamic and one pair electrostatic. In all three of these, overall I liked feedback over none.

As for DHT amp using no feedback, I have yet to hear one that has the dynamics, bass extension and tightness of a KT88/6550 using feedback...that is after taking account power output of the amp. But good DHT no feedback amps have glorious midrange, though not accurate IMO.

Regarding odd order harmonics being irritating and having increased perceived loudness, this is very difficult to pin down in one's audio system among all the other forms of distortions inherent down the chain, unless you are willing to deliberately increase the odd order harmonics in your amp and listen for the change. What I thought was irritating odd order harmonics arising from my amp using feedback was actually distortion arising from the source and boundary effect from room acoustics.

Mapman, I agree with you. The ears have the final say. That is why I posted. IME, negative feedback is beneficial.

Ralph, by "tightness" I'm referencing real acoustic bass instruments such as kick drum or stand up bass. Therefore, it is not an system artifact.

Getting back to my original point...here's a thought experiment. Let's say you design a tube amp with different levels of negative feedback, let's say in increments of 3 dB from 0 to 30 dB. Assuming you have a good speaker/amp match, what you you hear as you increase the negative feedback from 0 to 30 dB? This may be simplistic, but has someone actually performed this kind of experiment?

I thought KT88s are beam tetrodes, not pentodes?

I do like the sound of DHT amps without feedback in the right system. They have a certain magic to the sound that I think is missing in tetrode or pentode amps with feedback. IMO, DHTs are more expressive than life making tetrode/pentode comparably "dull", hence I can see why they are popular. However, I don't think DHTs are as true to life...I know many feel just the opposite.

Thanks Kijanki for the link.

Ah got it, Charles1dad. May be one day, if I have the right speaker, I'll get a DHT amp. But I'm not sure if I can deal with the heat. My OTL amp raised the temp of my listening room by 15 degrees F easily in the summer. I've owned KT88/6550/KT120/EL34 and OTL amps.

Good point.

Learsfool, this is all semantics. I have been playing classical guitar since high school, and have dabbled in piano and sax. I have attended concerts at some of the finest halls in the country (Symphony Hall in Boston, etc) and listen to live unamplified acoustic music on a regular basis (Jazz, folk, and classical). By tight, I don't mean bass that has been stripped of harmonic content and sounds dry. I mean muddy bass that has been stripped of harmonic content distorting the timbre of the instrument. Tight bass has initial fast transient attack followed by natural decay and rich harmonics. This can be heard with plucked stand up bass, low piano notes, kick drum, tympani etc. There are exceptions of course such as wind instruments, like church organ, tuba, etc.

Kijanki, thanks for pointing that out on the Stereophile article. One famous amplifier designer told me there is no such thing as totally zero negative feedback. Even the tubes themselves can have built in feedback.

Learsfool, I know "tight" is not a term most musicians use. But we audiophiles (and closet musician on the side such as myself) have our own set of terminology that will befuddle most musicians. We use many different terms to describe the similar, if not the same, thing (eg, instrument tone, tonality, timbre, overtones, harmonics).

Charles1Dad, go to these links:

http://www.hans-egebo.dk/Tutorial/tubes.htm Go to "Tubes become active" section.

http://www.diyaudio.com/forums/tubes-valves/178688-triode-plate-resistance-internal-negative-feedback.html

Learsfool, "neutral", in almost all cases, is a subjective audiophile term. IMO, only people truly qualified to use this term are recording engineers who have the capability to compare their recordings with the live performance that was recorded in their studios or venue. Don't get me wrong, as I've sinned too using this term in the subjective sense for lack of a better word.

As for "midrange", this can cover 200-300 Hz to 1-3 kHz depending on the audiophile. And yes as you state, this covers most of the frequency range of most instruments. That's why most audiophiles often proclaim the midrange is the most important because most of the music occurs in this range. Broad yes, but sometimes useful.