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Old 19th June 2012, 08:06 PM   #41
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The 50 Ohm resistors i crossed have to be 10 Ohm. So 25mV is developing over the 10 Ohms. That also sets the idle in the output stage.
The emitter loads of the input BJTs are bootstrapped with a copy of the output signal.
That way they see a high impedance. This is simpler then the current mirror you see here usually and works very well too. The collectors are connected to the output transistors and not to the opposite supply as usual.
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Old 6th July 2012, 08:11 AM   #42
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Hi Joachim,

I would like to build Your phono design as in post #1. I can not find BF246A. Can I use other type of Jfet?
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Old 6th July 2012, 01:48 PM   #43
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Yes, you can use other N-Channel J-Fets as long as Idss is higher then the current you want to send into the circuit. Which one can you get ?
J310 for example ? The higher the Idss is to begin with the more you can degenerate the Fet and that usually increases output impedance, thus improving PSRR.
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Old 6th July 2012, 03:43 PM   #44
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You can also use the J309 and there are other BFs.
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Old 9th July 2012, 07:14 AM   #45
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Thank you so much for your reply.
Can I use them j111 instead.
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Old 9th July 2012, 09:04 AM   #46
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Yes, J111 should work too. Idss is around 20mA, cutoff voltage around -3 to -10V.
You have to watch if there remains enough voltage over the 1kOhm pot.
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Old 10th July 2012, 08:36 AM   #47
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Thanks again. I will try J111 and J112 then. Hope it work.
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Old 10th July 2012, 11:24 AM   #48
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Yes, it will. I would set the current from 3.5 to 6mA.
Both, positive and negative side, the same.
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Old 19th July 2012, 09:51 PM   #49
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The work on the SBP ( Solar Batterie Poweramp ) made some progress.
I simplified the output stage to a CFA ( Szikley ) and added the possibility of current drive.
3 kinds of drive are now possible :
Voltage Drive
Current Drive
Open Loop ( output stage not in the feedback loop like Stasis )
Circuit diagram will follow when the prototype works as advertised.
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File Type: jpg Solar bat prot 1.jpg (334.2 KB, 404 views)

Last edited by Joachim Gerhard; 19th July 2012 at 10:02 PM.
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Old 19th July 2012, 11:51 PM   #50
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Thats it for today...
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