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In Reply to: RE: "And I knew that I was listening to several percent harmonic distortion." posted by Tre' on July 03, 2011 at 11:42:52
Good question (also posed by another responder). The design in question was a single 300B that used no feedback and was played reasonably loud. I therefore assumed (yup) that there was substantial distortion present. I still think it's likely, but I really don't know that. And again, it sounded good and got me thinking.
Follow Ups:
Here's was my point,
Let's say the speaker was rated at 96db
and the listening was done in a room (not outdoors)
And there are two amps and two speakers
and that 90db average is loud (it is in most listeners minds)
Here's where we end up,
1/8 of one watt from each amp will cause 87db SPL from each speaker.
Both speakers are in the same room so there will be 90db in the room.
Most listening rooms will have the reverberant field start at about one meter from the speaker so there should be 90db at the listening position.
A properly designed 300B SET amplifier will not have several percent harmonic distortion at the 1/8 watt output level.
Whatever harmonic distortion is present will be almost completely 2nd order and 2nd order harmonic distortion is not heard as distortion in music reproduction.
It's not the THD that matters but the amount of upper ordered distortions.
DHTs are very linear. That's why people build with them.
I think you had a favorable listening experience because the amps were DHT SET design (not in spite of it) and were producing less of the type of distortion that matters than other amps that you might have been familiar with up until that point.
Just my 2 cents...
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
While I'm happy to agree with you, be aware that there are folk around who don't. These people listen to '70s Japanese transistor amps because their THD specs are miniscule.
(The fact that they sound sterile and uninvolving is ignored! :-)) )
Regards,
"It's not the THD that matters but the amount of upper ordered distortions."
VERY few people realize this, bravo.
The reason is "masking" the louder lower component can obscure the higher / upper component. The higher the order the component is, the less it is masked relative to the fundamental or lower component. With music, the broad band content "hides" distortion much more than a single tone too.
When applied to RF where all out of band content was "BAD", THD made perfect sense, when applied to similar amplifiers topologies, it made some sense but when applied to totally different amplifiers topologies (like SS vs tubes) it became close to irrelevant except as a marketing tool.
FWIW, at least some time back, a single triode stage of a 6SN7 had a lower spectral content per gain than any other approach.
Best,
Tom Danley
Danley Sound Labs
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