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Old 29th March 2012, 12:51 PM   #121
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Quote:
Originally Posted by evanc View Post
...In the schematic the source of the 2sk170 is hooked throughout the potentiometer to the drain of the 2sj74...
Hi Evan,
your interpretation of the schematic is wrong (JFETs are drawn as if vertically mirrored). P1 is attached to Sources of both JFETs. In order to work, P-channel JFET needs its Drain to be more negative than its Source (and vice-versa for N-channel JFETs).

Google for : "Erno Borbely JFET frontiers"
It's two-part article that will help you understand and use JFETs
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Old 29th March 2012, 02:33 PM   #122
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Excellent thanks for the explanation...I will build this this weekend...Thanks again..Evan
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Old 29th March 2012, 05:50 PM   #123
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OK stupid question #2. Will this circuit run on 10vdc.? Could i decrease the values of r4 r5 r6 and r7 to drop less voltage there?
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Old 29th March 2012, 07:08 PM   #124
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Old 29th March 2012, 07:58 PM   #125
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I'll take that as a no...I said it was a novice/stupid question. My idea was to use the power supply that is all ready in the chassis. If this bit doesn't work out then oh well the ipad will only **** off neighbors two houses away instead of three....
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Old 29th March 2012, 08:20 PM   #126
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Quote:
Originally Posted by evanc View Post
...Will this circuit run on 10vdc.? Could i decrease the values of r4 r5 r6 and r7 to drop less voltage there?
I suppose you mean +/-10V ? You have to precisely describe the circumstances...
As you see, the F5 runs on approximately +/-24V. That's why there are 7812 and 7912 regs to lower the voltage to +/-12V. If you want to use the preamp in the same box with F5 why would you want to supply the preamp with "10V"?

Please be more descriptive if you expect meaningful answers...
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Old 29th March 2012, 08:29 PM   #127
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Sorry for being too brief, doesn't everyone know all about my system and what I want....? I am thinking about your preamp in the chassis with my DCB1. That runs on +/- 10 volts. I only want to amplify one source that is why I am not thinking of the installing with F5. Anyway thanks for putting up with my lack of knowledge. I'm trying, Really I am....
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Old 29th March 2012, 08:49 PM   #128
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OK, don't worry.
You can use the preamp with +/-10V PS.
Lower R6,R7 to 47-68R (in order to get 10-15mA through Q3/Q4)
Omit the 7812/7912 regs. Keep the RC filters (R1, R10, C1-C4).
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Old 29th March 2012, 08:54 PM   #129
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Nice...Thanks. Neighbors watch out....
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Old 29th March 2012, 08:54 PM   #130
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