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Why do audiophiles shun feedback in amplifiers?

I've owned several very highly regarded tube amps. Some of them allowed adjustment of the amount of negative feedback. I've always found some degree of feedback improved the sound...more realistic with tighter bass, dynamics, better defined imaging, etc. I have found amps with less or no feedback sound loose and diffuse with less dynamics... I know you should design am amp with excellent open loop gain before applying feedback. I can see the use of no negative feedback for low level amplification (eg, preamp and gain stage of CDP or DAC). So why this myth perpetuated by audiophiles and even many manufacturers?
dracule1
kijanki's avatar
kijanki
4,428 posts
 
It is not only 2nd harmonic, but also Intermodulation Distortion, Bandwidth, Output Impedance - practically everything. The key to avoid TIM is to limit bandwidth at the input to one that amp had before feedback (that extended bandwidth) was applied. This will be OK if amplifier had wide bandwidth to start with, otherwise reduced bandwidth will cause phase shift at higher frequencies and wrong summing of harmonics. Also, as I mentioned before, every amplifier has some form of NFB.
charles1dad's avatar
charles1dad
10,250 posts
 
I don`t agree that 'every' amplifier has NFB. There are some DHT SET amplifiers that lack NFB in their circuit.Some of these types of tubes are linear enough so that it is`nt necessary.My amp is one example(unless Israel Blume told me a fib,and I doubt that).
Regards,
kijanki's avatar
kijanki
4,428 posts
 
Charles1dad, It is possible but perhaps not very common. Everything depends on definition since even single unbypassed cathode resistor is NFB.
charles1dad's avatar
charles1dad
10,250 posts
 
Kijanki,
I believe your right in that the vast majority of amplifiers use some degree of NFB.I think DHT SET amps are a small niche that can be the exception.
Regards,
dracule1 OP
1,085 posts
 
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.
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