AVS Forum Addicted Member
Join Date: Nov 2006
Location: Colorado Springs, CO
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We know all amps distort. That's not debateable by sane people.
Amps have various amp linearities. If you read Self's book, he discusses them for typical class AB designs.
By attempting to control various issues in different amp stages, and using feedback, the non linearities can be reduced such that the amp's THD at the lowest point is well below audibility, at least according to what I have read (.3% THD or or so, for a pure tone.)
But there are factors which the above does not address.
Noise may be a factor. Some amps are more noisy than others. My Crown amp has been dissapointing when it comes to noise.
Speaker amp interaction has been blamed. Some sources claim that under certain cases, a speaker may draw high amounts of current causing distortion (as the amp's power supply can't manage and the voltage from the supply will sag.)
Some people say that when some amps overload, they have poor recovery.
As an amp is pushed towards clipping (usually considered to be at 1% THD if not directly measured,) the distortion will increase. Some amps measure their power at a more conservative point on this curve. So they may have more power than you think.
Music/Movies (especially movies) being highly dynamic, may run out of power more often than we think (I have no measurements to prove this.) So when someone says an amp may not be as good as another one, it may be that it's overloading more than the other one...it's power supply can't keep up, regardless of what the power specs say (and note that the power specs are usually based on a static 8 ohm load.)
I don't know that I believe an amp affects soundstage or has a poor midrange or other such statements, unless measurements could be provided to prove this. But I can believe that amps can sound different because they all distort. And may not distort in the same way under the same conditions. And you may not be able to measure this distortion with a simple THD+N test. You may need real world signals with the amp connected to a real speaker to see issues.
"But this one goes up to 11"