Non-feedback amplification topology and frequency

I had a Butler TDB-5150 (Tube/MOSFET hybrid multi-channel amp) that had no global negative feedback. It had these specs.:

Freq response: 20Hz to 20kHz (+/- 0.5dB)
Power Bandwidth: -3dB, 50kHz

So I would presume that not having feedback will not impose any audible frequency limitations...

-RW-

Jmacinnis, The issue here is how the amp will drive the speaker if it has no feedback. This article will explain what is going on:
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

IMO/IME amplifiers that operate without feedback are more musical as they make less odd ordered harmonic distortion. Since our ears use odd ordered harmonics to figure out how loud a sound is, this is arguably one of the more important human hearing rules! The use of feedback violates this rule.

However the audio industry does not like to talk about this, and is something that separates the high end audio community from everything else; we talk about it occasionally instead of never :)

Ultimately you have to be more careful of your speaker choice; this is doubly important because a speaker that requires the amp to have feedback will never be able to sound like real music- it will at best sound like a good hifi.

"Ultimately you have to be more careful of your speaker choice; this is doubly important because a speaker that requires the amp to have feedback will never be able to sound like real music- it will at best sound like a good hifi."

Atmasphere, I have to disagree with your opinion. I've owned both Atmasphere amp (M60) which uses minimal feedback and tube amps that use up to 20 dB of feedback. More often than not, I've found tube amps that use feedback sound more realistic and are more compatible with wider range of speakers than amps that use no feedback. I've looked into why audiophiles think no feedback is sonically superior, but I can't find any good reason to support this contention. Yes, NFB does increase odd order harmonics but the levels are low, and I doubt if anyone can actually hear them reliably. I've found most tube amps with no feedback to have less controlled bass, less dynamics, and subtle softening of the highs.

More often than not, I've found tube amps that use feedback sound more realistic and are more compatible with wider range of speakers than amps that use no feedback. I've looked into why audiophiles think no feedback is sonically superior, but I can't find any good reason to support this contention. Yes, NFB does increase odd order harmonics but the levels are low, and I doubt if anyone can actually hear them reliably. I've found most tube amps with no feedback to have less controlled bass, less dynamics, and subtle softening of the highs.

I did not state an opinion, but fact. Nor is it something I made up- this has been with us for a long time. You might want to read the article that I linked.

It is quite true that there are more speakers designed for amps with feedback than those without. And its also true that if you use an amp with no feedback (Power Paradigm) on a speaker that needs it (Voltage Paradigm) you will get a tonal coloration of the types you describe.

You are incorrect in stating

the NFB does increase odd order harmonics but the levels are low, and I doubt if anyone can actually hear them reliably

The fact of the matter is that slight increase in odd-orders are described as 'bright' harsh' 'hard' 'clinical' etc. by audiophiles, yet we are talking about distortion levels that may only be increased by a few 100ths of a percent! This is because the ear/brain system uses odd ordered harmonics to sort out how loud a sound is.

This is why two amps can measure flat on the bench, but one might sound bright and the other might not.

IOW the ear is considerably more sensitive to these harmonics than it is to human vocal frequencies.

General Electric proved this back in the 1960s- its not anything new.

Again I recommend you read the article and most of this will be made clear.