current versus watts

Hi Dob, I agree keeping distortion down is important. Distortion can hide detail. A lot of designers use global negative feedback to reduce distortion though, and this technique often results in subtle enhancement of odd ordered harmonics, specifically the 5th, 7th and 9th, that are used by the human ear to perceive the volume of a sound.

So the resultant sound will sound louder than it really is, in addition it will have brightness. Our ears are so attuned to these harmonics that even 100ths of a percent of distortion of them is audible: harsh, hard, brittle, clinical, bright, chalky, etc are all terms audiophiles use to describe this enhancement.

Thus it is often the case that the use of negative feedback is violating one of the fundamental rules of human hearing perception. So generally an ultra-low distortion figure is often a sign that global negative feedback is being used, and also that the amp may sound like a nice hifi, but will never sound like real music. IOW I am always suspicious when I see super low distortion figures.

"use of negative feedback is violating one of the fundamental rules of human hearing perception. "

Hello Ralph,

I spoke with Simon Thacher from Spectron and he is in full agreement with you as it relates to negative feedback in conventional amplifier.

He said that you are absolutely right and poor neagtive feedback, ripples from the power supplies and few other sources of odd harmonic distortions are "music soul killers" i.e. its not so much obsuring detail by even order harmonics as ear-piercing odd order harmonics.

Yet, Spectron rely heavily on global feedback. He explaiend that the crucial factor in negative feedback is transit time, the amount of time it takes from when an error is detected at the input until it is corrected at the output.

Thacher claims that Spectron use much faster digital logic circuits then anybody in the world. Their amp's transit time is less then 200 nanoseconds. Such an ultra-short transit time allows the amplifier to correct for many small errors; and the control loop can follow the input much more accurately WITHOUT generation of many odd (and even) order harmonic distortions and this is the main reason for positive "musical" reviews their amp receive.

All The Best
Rafael

Dob, yes, the transient time, propagation delay, plays a huge role in the effectiveness of global loop feedback. I am not sure exactly how fast an amp has to be though; even the fastest amps I have seen seem to have problems when feedback is applied. IMO the amp should be functional with or without it feedback.