Cascoded -MosFet- Zen without feedback - diyAudio
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Old 4th February 2006, 07:42 AM   #1
Tyimo is offline Tyimo  Hungary
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Default Cascoded -MosFet- Zen without feedback

Hi!
I moved the theme and open this thread beacause I didn't want to distub the conversation in the original Pass JFET Power Amplifier thread.

So, I will try again to ask and maybe some expert could be more focused to my "problem". :-)

I would like to build the ZenV8, but here in Europe-Hungary I cann't buy the Lovoltech JFets yet. So, I was planing to build the ZV8 circuit as it is ,but with only Mosfets instead of the Lovoltech JFet.
I asked Mr. Pass how about to use Mosfets instead of Jfet in the circuit. He answered:

"Absolutely.Just Cascode a Zen . My original design for the F3 was precisely that, but did not use feedback."

Vix built successfully a version of the Cascoded Zen, but he used some negativ feedback. I would like to build mine without feedback, like Mr. Pass did with his prototype circuit.

So, my old question is still:
How could we build a NNFB-Cascoded- Zen???

or, I have to ask Mr. Pass self: could you post here your prototype's schematic?

Greets:

Tyimo
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Old 4th February 2006, 09:02 AM   #2
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Hi, Tyimo

Sometimes we are flexible in thinking. When we see a number of 0.01, we easily claim that it is 0. When we have a feedback line with very small (ignorable) feedback, we could say NO feedback. If you post a circuit as you think, many will help you to get a nice result . . . I believe so . . .

Regards
jh
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Old 4th February 2006, 11:03 AM   #3
Tyimo is offline Tyimo  Hungary
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Hi JH!

O.K. For starting point here is Vix's modificated ZV8 version that works already but with a little feedback.

I hope He doesn't mind that I post here his schematic!

Greets:

Tyimo
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File Type: jpg cascoded zen by vix.jpg (39.5 KB, 600 views)
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Old 4th February 2006, 02:14 PM   #4
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If we increase R3 and P1 (at the same rate), we could have almost no negative feedback. (Meanwhile, we might need to reduce C2 down to 1uF.)

But, I do not know how it would work. Like to get other opinions . . .

Regards
jh
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Old 4th February 2006, 03:21 PM   #5
flg is offline flg  United States
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Well, Raising R3 and P2 is good, I think, but connect R3 to the +rail. This gets rid of the F.B. Get rid of R2... Just my 2cents...
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Old 5th February 2006, 04:38 PM   #6
Tyimo is offline Tyimo  Hungary
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Hi JH!

Do you mean something like this:

Tyimo
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File Type: jpg cascoded zen nnfb-v1.jpg (44.0 KB, 386 views)
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Old 5th February 2006, 04:40 PM   #7
Tyimo is offline Tyimo  Hungary
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Hi Flg!

Do you mean something like this:

Tyimo
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File Type: jpg cascoded zen nnfb-v2.jpg (44.4 KB, 377 views)
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Old 5th February 2006, 04:43 PM   #8
Tyimo is offline Tyimo  Hungary
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What would happen with the in the original ZV8 amp, if I would simply put an IRFP044 MosFet to the place of the Lovoltech JFet ?!?

Greets:

Tyimo
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Old 5th February 2006, 05:25 PM   #9
flg is offline flg  United States
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Hi Tyimo,
Yes, I beleive that would do it. You can now reduce your input cap substantially ($$$) because your input Z has gone way up vs. the other configuration.
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Old 5th February 2006, 05:26 PM   #10
Tyimo is offline Tyimo  Hungary
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And one more idea what Stephano wrote:

Greets:

Tyimo
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