Well, You could use a mosfet or a bipolar for the output transistor
however, I wouldnt put any other device in series with the diode path..
Of course , If you do.. Be sure to use a dummy diode stack to test it with a scope to make sure there are no spikes..
And if you are successful in getting a good waveform here then
you can bias the circuit for threshold..and then use another transistor for the control...
I found it easier to do it at the op-amp inputs, but this is another deal in itself
as you will have to find a single rail op-amp that will let you switch it to
the ground rail as close as possible to get cut-off and be able to switch at 30k plus speeds.
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