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Re: On a different note: Response to Morricab on Amplifiers

Posted by theaudiohobby (A) on February 10, 2007 at 01:10:37

In Reply to: Re: On a different note: Response to Morricab on Amplifiers posted by morricab on February 9, 2007 at 03:21:18:

"I am not sure this is a consensus opinion about SET no NFB amps about harmonic content preservation. I personally don't buy into that and I think it is much more reasonable to talk about audibility of distortions and which one is least offensive. I think of it more as an overlay on the music and the subjective effects of that overlaid distortion. "

It is best you read the whole text, cos he is referrring to the concept of benign distortions.

"You have to realize that a no feedback amp is most linear at its lowest power. This is not true for nearly all amps with lots of NFB. At low power we see the THD + noise is greater often than at high power."

Why is the a problem, when the the high feedback amplifier starts out which much lower, more than 100 times lower, THD in the first place. Moreover, the distortion of the zero feedback amplifier continues to worsen dramatically as the signal get more complex because that it has no feedback to maintain linearity.

"Now this rise at low power (relative rise as it is in %) is often attributed to noise floor but if that is the case then why do all these amps have such a high noise floor?"

Do have data to back this up, cos the archives at the usual suspects make nonsense of this claim?

"I suspect rather that it is more like what Norman Crowhurst explains happens when feedback is added to an amp. The level of distortion decreases but the order of the distortion multiplies"

I do not have access to Norman Crowhurst article or book on the subject, that being said, the level of distortion is still much lower than an equivalent zero feedback amplifier, whose distortion worsens dramatically, and it ain't just lower order, when an actual musical signal. If the amplifier is of the SET variety, then the non-linearities of the transformer also come into play.

Moreover, a zero feedback amplifier (especially one of the tube) variety by definition has a much higher output impedance, which has measurable and sometimes readily audible effect on the frequency response.

Music making the painting, recording it the photograph

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