Cascoded -MosFet- Zen without feedback

Tyimo · 4th February 2006, 07:42 AM

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

jh6you · 4th February 2006, 09:02 AM

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

Tyimo · 4th February 2006, 11:03 AM

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

jh6you · 4th February 2006, 02:14 PM

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

flg · 4th February 2006, 03:21 PM

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...

Tyimo · 5th February 2006, 04:38 PM

Hi JH!

Do you mean something like this:

Tyimo

Tyimo · 5th February 2006, 04:40 PM

Hi Flg!

Do you mean something like this:

Tyimo

Tyimo · 5th February 2006, 04:43 PM

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

flg · 5th February 2006, 05:25 PM

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.

Tyimo · 5th February 2006, 05:26 PM

And one more idea what Stephano wrote:

Greets:

Tyimo

4th February 2006, 07:42 AM	#1
Tyimo diyAudio Member Join Date: Nov 2002 Location: Hungary	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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4th February 2006, 09:02 AM	#2
jh6you Account Disabled Join Date: Aug 2002 Location: Near to the Pacific Ocean	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

4th February 2006, 02:14 PM	#4
jh6you Account Disabled Join Date: Aug 2002 Location: Near to the Pacific Ocean	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

4th February 2006, 03:21 PM	#5
flg diyAudio Member Join Date: Jul 2005 Location: North East	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...

5th February 2006, 04:43 PM	#8
Tyimo diyAudio Member Join Date: Nov 2002 Location: Hungary	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

5th February 2006, 05:25 PM	#9
flg diyAudio Member Join Date: Jul 2005 Location: North East	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.