Hello all!
I got one of my crazy ideas again.
I have a few R085 to play with, but have mostly stayed clear of them because of the negative bias supply requirement.
I get that one solution is to place the R085 in the top of the output stage like the DEF amp. That, however, requires it to be run in common-drain mode which as far as I know would drop the gain to 0 and also have a low output impedance (I would prefer a single stage amp and I also want a current source amp with high output impedance).
If I remember correctly, however, in the F6 Nelson uses the transformer in a nifty way to run the upper N-channel mosfet in common-source which got me thinking...
Does this trick work in general or is there something specific with the F6 topology? Could I build say a F2-ish amp but put the CCS on the bottom, a R085 on top and use this trick with a transformer to make the R085 operate common-source? Or dive deeper into crazy and use a P-channel mosfet on the bottom and configure it as a mu-follower =)
And if it does work, would it perform comparable to a normal common-source configuration with a negative bias supply or would it be inferior in some way?
I got one of my crazy ideas again.
I have a few R085 to play with, but have mostly stayed clear of them because of the negative bias supply requirement.
I get that one solution is to place the R085 in the top of the output stage like the DEF amp. That, however, requires it to be run in common-drain mode which as far as I know would drop the gain to 0 and also have a low output impedance (I would prefer a single stage amp and I also want a current source amp with high output impedance).
If I remember correctly, however, in the F6 Nelson uses the transformer in a nifty way to run the upper N-channel mosfet in common-source which got me thinking...
Does this trick work in general or is there something specific with the F6 topology? Could I build say a F2-ish amp but put the CCS on the bottom, a R085 on top and use this trick with a transformer to make the R085 operate common-source? Or dive deeper into crazy and use a P-channel mosfet on the bottom and configure it as a mu-follower =)
And if it does work, would it perform comparable to a normal common-source configuration with a negative bias supply or would it be inferior in some way?
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Exactly!
But if we take the F6 as an example:
If I've understood correctly in the F6 both the top and bottom N-channel FETs operate in common-source because of transformer magic.
So lets go further and lift the transformer secondary on the bottom FET and remove the capacitor. If I've understood correctly this makes the bottom FET operate as a pure CCS making it a single ended amplifier. The question, however, is if the top FET is still operating in common-source or if it has been converted into operating in common-drain?
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It looks like it will work fine. You’re right... the way the signal is presented between the gate and source floats it above the output so it should act as a common source stage.
I Guess only one thing to do now ... is to try it !
I Guess only one thing to do now ... is to try it !