Many here have jumped onto the M2 band wagen, but few have paid attention to the opto-biased output stage in detail.
We have, for example, discussed the use of different MOSFET pairs.
https://www.diyaudio.com/community/threads/complementary-power-mosfets.378024/post-6889027
Nelson has previously dropped some hints that it works well also in Class A/B.
But how ?
This is an attempt to analyse precisely that, using LT Spice simulations.
It is a waste, IMHO, not to use this clever OPS design in more applications.
For example, how about in a WHAMMY Power amp ?
Patrick
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Only an attempt to encourage people to understand how things work,
rather than just blindly copy and paste.
Patrick
rather than just blindly copy and paste.
Patrick
I think I recall reading in Nelson's thread "Official M2 Schematic," that he said his intended purpose of the three 1N4148 diodes was to give a smoother recovery from output voltage clipping when driving normal 8 ohm loads. The Pchannel side has a different number of diodes than the Nchannel side, intentionally.
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If any part of my analysis is in error, I am sure Nelson will care to put it right.
Cheers,
Patrick
Cheers,
Patrick
Assuming Nelson would agree, and someone has a serious interest :
I shall make available the Gerber of the above PCB with an integrated DIP8 opamp powered by the same supply.
So then you can build a WHAMMY power amp and start playing with opamp and MOSFET types.
But Nelson has to approve first.
Patrick
I shall make available the Gerber of the above PCB with an integrated DIP8 opamp powered by the same supply.
So then you can build a WHAMMY power amp and start playing with opamp and MOSFET types.
But Nelson has to approve first.
Patrick
Patrick,Only an attempt to encourage people to understand how things work,
rather than just blindly copy and paste.
Patrick
Although I can not (yet) fully appreciate the subtleties of the circuits, your posts and findings always give me a lot to consider and to learn.
Thanks for sharing!
What opamp tp choose from other than OPA551 for a power WHAMMY ?
For +/-24V rails, OPA604 is well known.
ADA4098 will just make +/-25V.
Above +/-25V, choice is rather limited.
I found ADA4700, which is quite similar to OPA55x but can go as high as +/-50V.
Other candidates -- LTC2057HV, and perhaps ADA4522.
Patrick
For +/-24V rails, OPA604 is well known.
ADA4098 will just make +/-25V.
Above +/-25V, choice is rather limited.
I found ADA4700, which is quite similar to OPA55x but can go as high as +/-50V.
Other candidates -- LTC2057HV, and perhaps ADA4522.
Patrick
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Maybe Dreadnought in the Store might be a useful starting point for a low-complexity, higher voltage, discrete front end?
btw, if anyone's interested: to hand-calculate bias currents, assume (a) LM285 voltage is 1.235V per datasheet ; (b) Vbe of KSA1220A is 0.60V
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btw, if anyone's interested: to hand-calculate bias currents, assume (a) LM285 voltage is 1.235V per datasheet ; (b) Vbe of KSA1220A is 0.60V
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The M2 OPS is a complmentary push-pull MOSFET output buffer.
The original M2 has a JFET frontend with no global feedback.
So, for me, a fitting discrete frontend is either an all-FET VAS with no global feedback, e.g our own HAGS :
https://www.diyaudio.com/community/...a-zgf-headphone-amplifier.225577/post-3395149
or if it has to come from Pass, an F5-Pre (single ended version).
But a power WHAMMY is an easy starting point.
Cheers,
Patrick
The original M2 has a JFET frontend with no global feedback.
So, for me, a fitting discrete frontend is either an all-FET VAS with no global feedback, e.g our own HAGS :
https://www.diyaudio.com/community/...a-zgf-headphone-amplifier.225577/post-3395149
or if it has to come from Pass, an F5-Pre (single ended version).
But a power WHAMMY is an easy starting point.
Cheers,
Patrick
Recently there is an IXTH26P20P that seems to complement IRFP250 close enough with somewhat not so painful pricing. 🙂
An experienced power amp builder has kindly promised to do Alpha Test.
Opamp has differential inputs.
Patrick
Opamp has differential inputs.
Patrick
Since Mark mentioned a discrete frontend in post #10, maybe it's good to show an example.
Not fully optimised yet, but in principle it works.
But one at a time.
Patrick
Not fully optimised yet, but in principle it works.
But one at a time.
Patrick
Not toasted.
Just some no-name resistors of the right value I have lying around.
Good enough for alpha test.
Patrick
Just some no-name resistors of the right value I have lying around.
Good enough for alpha test.
Patrick
I was asked to post a schematics for the opamp front-end power amp.
This is still pending alpha test, so draft only. Not proven.
Patrick
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This is still pending alpha test, so draft only. Not proven.
Patrick
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