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In Reply to: RE: RH84 test amp: driver stage wiring change = lower THD% posted by deathtube 667 on September 15, 2016 at 16:46:39
The 12AT7 isn't as linear as many other 9-pin dual triodes. Distortion characteristics can change considerably with a relatively minor change in operating conditions. Not sure if that's what happened in this case, it's just one more possibility in addition to the things mentioned below. Didn't you say earlier that the distortion in this amp was over 1%?
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Buy Chinese. Bury freedom.
Follow Ups:
The THD was over 1.5% @ 1.2W the first time I wired up this circuit around a year ago.
Now THD is at .70% @ 1.2W with the circuit adjustments I have made recently , including the driver stage wirings.
You may want to review some of the earlier threads I had posted which noted other circuit/performance changes.
"The THD was over 1.5% @ 1.2W the first time I wired up this circuit around a year ago"
No, you reported over 1.5% just three weeks ago. That's why I was surprised to see these numbers suddenly looking better. What happened in-between?
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Buy Chinese. Bury freedom.
My first attempt with an RH type circuit was critiqued by the designer a long time ago.
All those posts are still in the archives.
More recently, I started looking at the RH type circuit again and tried G2 regulation with gas regulator tubes, but the distortion performance and noise was worse than my earlier/first attempt.
After that, I posted a thread that documented some circuit changes that reduced distortion by about 50%.
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