DIY-Pass-OP with only N-Fets ?

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#4
You will probably like this one (from a forselltech pdf):
 

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#6
Bernhard said:
Is it possible to built a DIY OP with N Fets only?
Click to expand...
Quite possible, in the same way they used to with tubes.

An N channel differential pair is biased by a resistor or an N channel current source to the negative rail, and the Drain of the right hand (feedback Gate) device drives either a current source (N channel of course) or a resistor. This Drain also drives the Gate of an N channel output follower whose Source connects to the negative rail through either a resistor or current source. This source is the output of the amplifier.

Now this circuit will naturally have a large positive offset, so if you want to direct couple it, you have to insert a voltage drop (could be a battery, for instance) between the Drain of the 2nd diff pair transistor and the Gate of the output device.

If this isn't clear, I'm certain that one of our artistic readers will render us a schematic.

:wiz:
 
#7
Re: Re: DIY-Pass-OP with only N-Fets ?

Nelson Pass said:

Now this circuit will naturally have a large positive offset, so if you want to direct couple it, you have to insert a voltage drop (could be a battery, for instance) between the Drain of the 2nd diff pair transistor and the Gate of the output device.
:wiz:
Click to expand...


Wow, you did read my mind.

In the end I need +/- 160V rails and +80V offset to drive a PL519 tube.
 
#8
lohk said:
You will probably like this one (from a forselltech pdf):
Click to expand...

This uses not only N-fets, but also P and self conducting (?) and is not single ended.

🙁


Xray said:
Mr. Pass has an article at http://www.passdiy.com/legacy.htm.
Click to expand...

The page cannot be found
The page you are looking for might have been removed, had its name changed, or is temporarily unavailable.

🙁


I like to use IRF460 everywhere want to make it work as a subtractor: Signal - negative Voltage = Signal with positive offset.

Maybe I can render Nelsons wors to a circuit 🙂
 
#13
This is what I like to build, just the problem is that the Fet in the upper right corner is a P.

Nothing is wrong with P-Fets so far, but I don't know any high voltage P-fets.

Are there any ?

Does the circuit look ok ? Just the +80V dc offset missing and one P-fet too much.


Could I built a high voltage aleph / aleph-X / X-amp ?

I want the best sound possible to drive plasma tweeters. 🙄

With X circuits, is it ok if I us only one output connected to the gate of the tube and leave the other one open (?)

By the way, the aleph is just a discrete op amp but with a dynamic current source which gives better eficciency, but does not make the sound better, right 😕

As I do not need high currents, I do not need the dynamic current source, right :scratch:



plasmaop.jpg
 
#14
It seems a bit hard to find a high volt P-Channel mosfet, I can see your problem.
Could something like this do the trick! See attached file.

If you only uses one of the outputs on an X amp, you won´t get any X.

My opamp is based on aleph sirciuit without the active currentsource, it is not needed as long as it runs as a frontend.
 

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