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Old 22nd October 2006, 07:11 PM   #1
Fuling is offline Fuling  Sweden
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Default A chopped Mini-A with Jfet input stage

Well, since the dynamic CCS is gone it doesnŽt qualify as an Aleph at all, but what do you guys think about this:


Edit: I forgot to draw a few things on the schematic.
Output transistors are IRF9530/IRF530 with 220R gate stoppers, rails are +-12V and Iq=1,3A
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Old 22nd October 2006, 07:12 PM   #2
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Or this (more questionable...):
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Old 22nd October 2006, 08:09 PM   #3
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second version looks as safer bet
in both cases you need lag compensation across nfb resistor (15K ; 12K)
mebbe you can try with one range up-scaled nfb resistors (multiplied with 10) so you can use film cap in divider;

besides ,referencing bases of cascodes to intersection of two 47 ohms resistor is mebbe better........

besides besides-don't take me serious, I'm just toob boy
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Old 22nd October 2006, 08:19 PM   #4
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IŽm not so sure that the cascode circuit is necessary, only the change from IRF9610 to BF245C (or some other Jfet) should decrease the input capacitance quite a bit I think.
When I get the time IŽll hardwire a prototype and see how simple it can get before losing performance.
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Old 23rd October 2006, 06:57 PM   #5
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You will want to use Fairchild or Harris for the 9530 part,
as they have lower distortion in Common Source applications.

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Old 23rd October 2006, 09:05 PM   #6
Fuling is offline Fuling  Sweden
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Thanks for the advice!

I have a another circuit in mind too that I will post within a couple of days, something between this and a Zen.
When I look into my crystal ball I see a lot of prototype building and testing the next few weeks
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Old 26th October 2006, 03:57 PM   #7
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My latest "invention":

The AC and DC values are measured on a working prototype, not simulated. Max output voltage is 20Vp-p with 24V rail (missing in schematic).
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Old 26th October 2006, 04:55 PM   #8
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Quote:
Originally posted by Fuling
My latest "invention":

The AC and DC values are measured on a working prototype, not simulated. Max output voltage is 20Vp-p with 24V rail (missing in schematic).

nice

mebbe you can try dissimilar jfets for cascode?
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Old 26th October 2006, 05:01 PM   #9
Fuling is offline Fuling  Sweden
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Quote:
mebbe you can try dissimilar jfets for cascode?
I must ask: For what reason?
I need all the current I gan get to drive the mosfet, and BF245C seems like a good choice. I tried BF245B at first but then I only got 5mA instead of 9mA.
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Old 26th October 2006, 05:28 PM   #10
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here it is
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