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In Reply to: RE: RH84 : CCS regulator drop out ... posted by deathtube 667 on January 22, 2015 at 03:18:00
i thought the lm317 needed to be bypassed with an SE circuit?
Follow Ups:
After removing the CCS bypass caps, I measured with ARTA at 1W and got horrid distortion , THD = 42%.
I didn't realize that the bypass cap was needed for correct circuit operation since I never tried LM317 as a CCS before.
I took out my scope and looked at the output of the amp, the resulting waveform was like a sine on the positive and a weird looking distorted square wave on the negative. It was really odd looking.
Next, I checked the driver stage and it was function normally.
After checking the EL84 plate, I saw the odd distorted signal again, so I knew it was probably the CCS.
But it was not until I read your post that I decided to bypass the CCS with some 22uF caps on jumper leads that everything worked again.
I'll have to try another set of 100uF bypass caps and see if anything changes.
Needless to say, not the most fun evening but it was informative, LOL.
Of course it does.
But the above is about DC performance improvement after elimination of leaky cap. The cap must be good. As for voltage value, twice the bias voltage I.e. cathode voltage is probably the best choice.
******
http://rh-amps.blogspot.com/
With B+ off the rectifier (UF4007 full wave) of 300VDC :
Total power output before clipping : 3W RMS
Gain = 6.36
THD = 2.43% @ 2.75W RMS measured with ARTA
2nd harmonic = -34.64dB, 3rd harmonic = -36.62dB ,
4th harmonic = -48.47dB, 5th harmonic = -55.28dB
60 cycle below -80dB, 120 cycle below -60dB
I failed to match the designers benchmark of 1% distortion at 4W RMS.
Perhaps deviations from the original design or using cheap AES PT-31 OPT's is a contributing factor.
That is it for now.
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