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Re: BTW morricab

I won't disagree with you that OTL amps sound superb. But I have heard a few transformer coupled ones that are on the same level and very few SS amps that are at that same sonic level.

The issue is not distortion per se but where it lies with regard to human perception. Humans simply don't hear low order harmonic distortion up to at least 1% (for 2nd harmonic) yet can hear even 0.01% of ninth harmonic. You see the problem. Pursuing distortion reduction with feedback does indeed reduce the lower order harmonics but it creates mulitudes of low order higher harmonics. It is not about some idealized sense of perfection, the distortion merely needs to be invisible to the human perception. High order harmonics are not invisible to human hearing but moderate levels of low order harmonics are. This is because the human hearing mechanism is effectively masking these harmonics with its own self-generated distortion. What is measured is not necessarily what is perceived and the last time I checked the listener was the final arbiter not the oscilloscope.

It is also used as a crutch for poor circuit design. You can see this in most feedback SS amps by looking at the increase in THD as a function of frequency. This correlates generally quite well with a drop in damping factor at high frequencies. What is going on there? WEll, the feedback is not effective at high frequencies thus the drop in damping factor and the increase in THD at high frequencies. The worse the design the more dramatic the increase in distortion. I think you can imagine what effects this might lead to. In addition it will affect the dynamic response of the amp in the bass vs. the high frequencies because one is being effectively controlled by feedback and the other frequencies are not. This will most certainly cause phase shift and other sonically audible attributes.

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