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In Reply to: RE: THD% estimate a bit too high ... posted by deathtube 667 on October 18, 2016 at 20:22:44
Probably some distortion cancelling between driver and output tube.
My numbers are just the output tube.
Tre'
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"Still Working the Problem"
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I doubt it from the measurements DDT posted... distortion cancellation typically results in 2nd and third distortions equalling each other because only the evens "cancel"
when you see a fft of a SE amp that doesn't have the typical dropping in distortion as harmonics go up then you have either a saturating output or driver / output even order cancellation.
dave
FWIW, Rage had a similar SE 2A3 circuit using Magnequest OPT + JJ 2A3's (not sure of the plate load or biasing) that he reported getting 1.5% THD @ 1W.
He was probably trying to copy what DF/JM did.
No matter what anyone would assert, JM will say DF is the greatest tube amp builder in the world.
The numbers I showed from the on line sim were just for comparison to each other, not for comparison to what others have done.
My numbers show that when the current is increased, increasing the plate dissipation, and the load impedance is increased from Dennis' operating point, the distortion goes down.
That flies in the face of Dennis' assertion of the idea of "thermaly stressed", what ever that means.
"...Rage had a similar SE 2A3 circuit using Magnequest OPT + JJ 2A3's (not sure of the plate load or biasing) that he reported getting 1.5% THD @ 1W."
I guess my assertion would be, if Rage was using Dennis' plate load and biasing and then increased the current and increased the load impedance his number would get even lower.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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