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Old 9th October 2012, 04:04 PM   #3351
shaan is offline shaan  India
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Shaan that is a fresh build, its only some news over the phone. I will see and listen at a point. Has to solidify in build details yet. 200mA is his per rail total, 170mA his output stage. It just gives 40dB OLG, 33kHz OL-3dB and 13dB FB if you close the loop in LT SPICE, maybe he misses some damping, who knows. What current you draw in your 1K2 resistor CCS on your amp? Just tell me the voltage drop over those. Is it in 12.5 to 15mA ballpark? That will help to choose JFETs and to see how near those amps are between them.
The current in the 1K2 resistor is indeed 12.5mA.
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Old 9th October 2012, 04:08 PM   #3352
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Amps alike.
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Old 9th October 2012, 04:16 PM   #3353
shaan is offline shaan  India
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Still you bypass the diodes with an electrolytic for AC in your amp. What goes on if you snub that cap with 0.33R 1uF MKP?
I used the cap to bypass the diodes for the AC currents in the VAS (see attachment, green trace is current variation in diodes, red trace is AC current through cap, 8uA through diodes vs 60uA through cap!).

Now, why I did this? Coz its common practice, and makes sense.
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Old 9th October 2012, 04:21 PM   #3354
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...And has the heavy influence that detracts from the diodes, and you can play with bypass quality...
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Old 9th October 2012, 04:23 PM   #3355
shaan is offline shaan  India
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Amps alike.
Yes. However, this current controls the VAS current through the input BJTs, if I'm not wrong.

VAS current may be different if there are different or no degeneration and different device gain, the resistor current still being 12.5mA.
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Old 9th October 2012, 04:27 PM   #3356
shaan is offline shaan  India
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...And has the heavy influence that detracts from the diodes, and you can play with bypass quality...
Yes, the cap I placed their was chosen from the best I found soundwise. And I have experience with some good looking expensive electros making an otherwise good amp sounding like puke!
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Old 9th October 2012, 04:30 PM   #3357
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Yes. However, this current controls the VAS current through the input BJTs, if I'm not wrong.

VAS current may be different if there are different or no degeneration and different device gain, the resistor current still being 12.5mA.
Driver can up or down its current by trimming your 220R cascode load that sits between B,E. 1K2's CCS (resistive) current carries the feedback resistors feed also.
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Old 9th October 2012, 04:33 PM   #3358
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Yes, the cap I placed their was chosen from the best I found soundwise. And I have experience with some good looking expensive electros making an otherwise good amp sounding like puke!
Was it an orange one if I remember well? Looks like German make, or something different?
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Old 9th October 2012, 04:38 PM   #3359
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Driver can up or down its current by trimming your 220R cascode load that sits between B,E. 1K2's CCS (resistive) current carries the feedback resistors feed also.
Yes. But I was particularly talking in respect to the resistor current only. There may be many more ways to change the current through the VAS, like increasing the PS voltage.
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Old 9th October 2012, 04:40 PM   #3360
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Was it an orange one if I remember well? Looks like German make, or something different?
It's a Keltron 100uF/40V. Indian make, orange.
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