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Some quick measurements...

I rigged the circuit up (as above) and made some quick measurements...

Following the THD numbers are the dominant harmonics in order of descending relative amplitude.

With a GE 6AR8:
---------------

Gain ~ 0.75

THD at max gain, 1V RMS in: 0.48% 2nd-3rd-4th harmonics
THD at 50% gain, 1V RMS in: 0.87% 3rd-2nd-5th-4th harmonics (larger THD value may be mostly noise)

THD at max gain, 5V RMS in: 2.7% 3rd-2nd harmonics
THD at 50% gain, 5V RMS in: 3.2% 3rd-2nd-4th harmonics (larger THD value may be mostly noise)

-6dB attenuation at Vg1 = -4.7V
-10dB at -5.9V
-20dB at -7.7V
-30dB at -9.3V
-40dB at -10.2V
-70dB attenuation at Vg1 = -12V or greater

With a RCA 6JH8:
---------------

Gain ~ 1.2

THD at max gain, 1V RMS in: 0.5% 2nd-3rd-4th-5th harmonics
THD at 50% gain, 1V RMS in: 0.67% 3rd-2nd-5th-4th harmonics (larger THD value may be mostly noise)

THD at max gain, 5V RMS in: 3.5% 2nd-3rd-4th-5th harmonics
THD at 50% gain, 5V RMS in: 6.7% 2nd-3rd-5th-4th harmonics (larger THD value may be mostly noise)

-6dB attenuation at Vg1 = -4V
-10dB at -5.3V
-20dB at -7.6V
-30dB at -9V
-40dB at -10V
-70dB attenuation at Vg1 = -12V or greater

Looks like this would make a good phase splitter as long as you keep down around 1V RMS in. THD is OK, and the spectra looks good, at 1V in. At 5V there's a lot of distortion.

The gain control seems to work really well, not introducing a lot of distortion as the gain is cut back.

Pete


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  • Some quick measurements... - Pete Millett 09:27:23 07/10/04 (2)
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