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In Reply to: RE: SE 6V6 triode : effect of plate to plate feedback ... posted by deathtube 667 on August 26, 2016 at 09:29:49
I am curious as to how you dertermine "max power out" for each variation? Also why are the distortion numbers for the feedback version different from the non-feedback version? I would think that the term "max power" would be referenced to some arbitrary distortion number and that referenced matched in the two cases so a better comparison can be made.
dave
Follow Ups:
For max power out, a scope probe is hooked up across a load resistor on the OPT secondary.
I run a 1KHz test signal from my soundcard into the amp and look at the point where the waveform clips, then back off until the sinewave looks undistorted.
I also have a true RMS voltmeter across the load resistor to record the AC signal voltage and use the typical ohm's law equation for power.
As for why the THD% is lower with local FBK than non-feedback version, that follows every SE pentode class circuit I have ever tried building.
I guess the conflict I see here is the visual clipping which is a very subjective thing and the harmonic distortion measurement which is purely objective are not agreeing with each other.
In order to make a "fair" comparison either the output power or the harmonic distortion (clipping) should be held constant and then the other result documented. Of course this doesn't take into account the distortion spectra but for a SE amp where 2nd order dominates the gross distortion figures things should line up fairly well.
dave
One problem is that the internal sine generator in ARTA is in 1dB steps.
I would need a way to fine tune the signal going into the amp so the output signal over the load resistor can be held with more precision.
Then I could get the same power output and compare THD% when in non-feedback vs. feedback modes.
Or I could use my external signal generator, but that tends to output more distortion than the soundcard.
Thanks for your comment.
Arta is limited to 1dB increments on the audio generator? Wow...
Even so that is in the voltage realm and the increase of 1dB of voltage is about 25% more power leaving the maximum variation between any two settings at 12.5% and statistically you will probably end up in the 3-10% range of variation.
dave
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