Wien bridge audio oscillator keying: SOLVED ?

 Taking another look at the Wien bridge single pot audio oscillator circuit and keying.  After trying the 2n7000 across the various gain control feedback resistors (R10, R5, R9) it occurred to me to try the 1n4148 diode pair.  The keying idea is to lower the gain of the circuit below one overall which is required for a sine wave oscillation.  Since the 2n7000 is ON when the gate is several volts above the source this works perfectly for keying.  When the gate is pulled low by the key the 2n7000 is turned off which allows the circuit to oscillate.  The RC pair on the 2n7000 gate results in a nice ramp down of the tone (in my opinion, others may find it mushy ?).  Note that the ramp up is from the oscillator start-up.

But the problem with the keying circuit was a leading edge glitch that resulted in a popping noise at the start of the code element (keyed tone).  Then I tried connecting the 2n7000 via a series capacitor thinking that the direct connection may have caused the glitch - no help.

Finally I tried moving the 2n7000 to the pair of 1n4148 gain stabilization diodes.

  While the leading edge glitch is still present it seems to be small enough that it isn't audible (or visible) on the amplified output.

output at pin 1 of LM324 with a small leading glitch

output after audio amplification, no audible leading glitch

BTW, this concept of keying an oscillator by reducing the gain below one (part of the Barkhousen criteria for oscillation) was introduced to me in an article by Denton Bramwell,K7OWJ, in QST:

Why not use the K7OWJ circuit ?  Because the phase shift oscillator frequency can't be controlled with a single pot and as shown the Wien Bridge audio oscillator now can be frequency controlled with a single pot.

So on to the next step:  what to do with that unconnected op-amp section ?

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm