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Old 20th January 2013, 09:44 AM   #9061
AndrewT is offline AndrewT  Scotland
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post9058.
Why has R16 replaced the CCS jFET?
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Old 20th January 2013, 10:05 AM   #9062
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by AndrewT View Post
post9058.
Why has R16 replaced the CCS jFET?
It was an experiment... I found it suited better my actual preamp - amp arrangement.

The ccs jfet should be there following the pdf.
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Old 20th January 2013, 10:31 AM   #9063
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In that case a 100n FT-3 will open it wide.
Ricardo

I think to try Salas recomendation of using 2 x 2.2 uF PIO K75-10 russian bypassed with 0.1 Ft-3 instead of obbligato premium gold 4.7 uF

do you think that would bring Improvement - obbligatos are very nice
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Old 20th January 2013, 12:45 PM   #9064
RCruz is offline RCruz  Switzerland
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DIY and listen
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Old 20th January 2013, 01:04 PM   #9065
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Quote:
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thank you for reply
I have listened at least 100 Hrs but still think that Is missing air
OK,
I degenrated the BF845B with a 33R resistor. Now have 14.5V at its drain. Nothing else has changed. Getting 8.1V drop from the LED's. Drain of Jfets are at 8.1V. THey are dropping 32mV across Rs, so all is good there. GAin jfet is still at 5V, but it seems easiest way to deal with this is to reduce degenaration or add higher Idss Jfet. Perhaps that is the problem, I used a higher Idss JFets, so it is causing greater degeneration with current 43R resistor. Not sure how the gain jfet and buffer plsy into setting of resistor, but all that is farily tweakable. I have to figure out why I cant get voltage at TP2. I have checked all traces. No shorts. Values are good and I can write them out if you like. Based on your measurements, RCruz, I need to degenerate the BF845 more, but this is simply about current level to LED's. How would it affect the setting of the collector of the BC560.

I have On semi BC560 and Fairchild BF845. I have checked the layout, and it is correct.
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Old 20th January 2013, 01:10 PM   #9066
Salas is offline Salas  Greece
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Quote:
Originally Posted by RCruz View Post
It was an experiment... I found it suited better my actual preamp - amp arrangement.

The ccs jfet should be there following the pdf.
Simplistic NJFET RIAA ...and he scratches his head.
Lesson is some things are particular to systems and tastes and there is no substitute than checking them out personally if intrigued. Same with parts and so on and so forth...
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Old 20th January 2013, 01:14 PM   #9067
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Salas,
Any ideas?
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Old 20th January 2013, 01:15 PM   #9068
Salas is offline Salas  Greece
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Buzz, is it possible your IDSS selections are far off for all Jfets? Can you describe the method you measured them exactly? Also DMM type and how you wired for testing?
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Old 20th January 2013, 01:23 PM   #9069
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I have 31mV across input fets, RCruz has 29mV. THey were Idss matched to 8.5 and 8.6mA. THE output fets are higher Idss, in the 9's, as I did not have any more good matches in the 8's. THey wer matched using 12V battery setup and 1K resistor. While not 10R, my results on FE are very close to RCruz, so nothing is too far off. I use tenma DMM for measuerments. I can degeneraete the BF more, but it did not seem to affect anything. Only thing not in the ciruict is output coupliing cap and its bleeder, as it should not affect the outcome. THe outpu stage JFet could be degnerated less, but I am unsure how it affects the RIAA. It should not affect Zin, as long as the Rl is not changed, correct. Not of that explains why i cant get a voltage across the collector of the BJT.
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Old 20th January 2013, 01:27 PM   #9070
RCruz is offline RCruz  Switzerland
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Hi buzz

Seems you might have trouble with the first stage Voltage setting trimmer.

I once did not get Q2 collector voltage because the trimmer did not go low enough.
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