F5 Headamp with Opamps ?

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1) Nothing. Just less voltage headroom.
Try it in Spice.

2) Because in the Spice model, the MOSFETs are not perfectly matched.
So you should be prepared to adjust the values of R5, R6 to adjust bias and DC offset.
Just the same in F5-HA.

3) Actual dissipation at 150mA is < 100mW. So 1W is enough .


Also, note that the schematics in post #18 is there to illustrate a means to tame overshoot without using a cap in the feedback loo.
The penalty is that the output FETs will have to delivery a lot more current for any signal > 10kHz.
So if you want to be kind to the FETs & power supply, I would still use post #7.

Any you should also be prepared to change the cap value, especially when you are using a different opamp.
I would start with 1nF MKP.


Patrick
 
I'm trying to wrap my head around this circuit:
isn't it about the output stage of an OpAmp that makes this circuit work and that lets you draw the parallel to an F5?
An OPA604 however is said to have "all-NPN output drivers".

What is it that makes you think that this is an unobtanium replacement more worthy than a pair of BJTs?
 
Think this way :

Opamp V+ = 2SK170 drain
Opamp V- = 2SJ74 drain
Opamp +IN = JFET gate
Opamp Out = Opamp -IN = JFET source

When you apply a signal to the input, the loading resistor causes the opamp to consume current,
This current will appear as an increase in current in V+, and a decrease in V-.
These current changes drives the MOSFETs, just the same in the F5-HA.


Patrick
 
Hello,

I had an idea but I did not know how to implement it, that's why I was interested in your topic.

I have always been fascinated by circlotrons and I would have liked to make one.

Build The Amazing FET Circlotron | Pass DIY

Mike Rothacher turned the F5 into a circlotron and you replace the Jfet by opamp.

If we merge the two ideas it could look like this :

An externally hosted image should be here but it was not working when we last tested it.


Do you think it is possible to made an amplifier like this ?

This schematic is just a mod of yours.... but dont work

thanks
Best regards
Sébastien
 
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> This schematic is just a mod of yours.... but dont work

So what is your question ? How would I make it work ?

I think you should ask Michael instead, since the circuit posted here works with fixed rails. Not a circlotron.

Alternatively, google "tubecad" and "opamp circlotron". John Broskie has published many versions with explanations.
e.g. Aikido PP & Solid-State Circlotron


Best,
Patrick
 
Thanks to your answer,

The question was "Do you think it is possible to made an amplifier like this "

the answer could have been, it could work..., or it would never work !

I asked this question about using the bootstrap op amp with a single power supply and only one mosfet

I think Michael does not like aop and Broskie dont use bootstraped opamp
 
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I do not know how many hours I would need to figure out and give you a definitive answer.
Quite honestly it is irrelevant to the circuit discussion here, and I have other priorities.
If you tried it already in Spice and it does not work, then chances are not so rosy.

I am sure you can figure out how to convert polarity of Michael's circuit to use 2SK170 and IRFP9240 instead.
Then there is no more motivation to use opamps.


Cheers,
Patrick
 
Think this way :

Opamp V+ = 2SK170 drain
Opamp V- = 2SJ74 drain
Opamp +IN = JFET gate
Opamp Out = Opamp -IN = JFET source

When you apply a signal to the input, the loading resistor causes the opamp to consume current,
This current will appear as an increase in current in V+, and a decrease in V-.
These current changes drives the MOSFETs, just the same in the F5-HA.


Patrick

Hi Patrick,

could you please tell , how its different from getting the output of opamp from its power supply pins (via resistors between power supply and opamp power pins) as in this amp, rather than from its output pin (more conventional way) .. what advantages of using the power supply pins for getting output of opamps to next stage..
 
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