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
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?
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
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
OK, thx, I was thinking too complicated.
How would you bring this schema to power amp dimensions?
How would you bring this schema to power amp dimensions?
Go back to John Curl's schematics, which were meant for power amp.
He was most likely using Toshiba power MOSFETs, judging from the bias voltages.
Patrick
He was most likely using Toshiba power MOSFETs, judging from the bias voltages.
Patrick
Hello Patrick
Did you do any other tests ?
I have some OPA604.
It could work with lateral mosfet ?
thanks
Did you do any other tests ?
I have some OPA604.
It could work with lateral mosfet ?
thanks
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I have not tried others.
Lateral has low Vgs at the same bias and will therefore reduce loop gain.
Does not mean that it will sound bad.
You just need to try.
If you have all the parts it will only take you a couple of hours.
And yes, the concept is not new.
You can find many such examples.
Patrick
Lateral has low Vgs at the same bias and will therefore reduce loop gain.
Does not mean that it will sound bad.
You just need to try.
If you have all the parts it will only take you a couple of hours.
And yes, the concept is not new.
You can find many such examples.
Patrick
http://www.diyaudio.com/forums/atta...30540-f5-headamp-opamps-jc-ohpa-proto-sch-png
what is the role of the diodes ?
with hexfet there is no risk of thermal drift?
Thanks
what is the role of the diodes ?
with hexfet there is no risk of thermal drift?
Thanks
> what is the role of the diodes ?
Over current protection.
> with hexfet there is no risk of thermal drift?
Not if you have sufficient heat sinking.
Proven in prototypes.
Patrick
Over current protection.
> with hexfet there is no risk of thermal drift?
Not if you have sufficient heat sinking.
Proven in prototypes.
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 :
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
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
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
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
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
Actually all discussed 7 years ago.
The Amazing Fet Circlotron by Mike Rothacher
Posts 114~116, 142~144.
Patrick
The Amazing Fet Circlotron by Mike Rothacher
Posts 114~116, 142~144.
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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