CPO => Keying Added to LM386 Wien Bridge Audio Oscillator

Made several attempts at adding keying and may have found a winner.

First, using a 2n7000 MOSFET keying transistor, pin 3 of the LM386 was shorted to ground when key up which turns off the oscillator, with a capacitor on the gate the keying is shaped.  This works but might be considered too mushy, adding weight to the code elements:

blue trace is the key input

Second, the 2n7000 was moved to pin 7 of the LM386 to act as a mute.  It does but was thumpy, clicky and mushy, no good.

Finally, the 10k ohm feedback pot was split into two resistances in series.  A 4.7k ohm resistor in series with 2.2k ohms.  Then the drain and source were connected to both terminals of the 2.2k ohm resistor (actually still a 10 turn pot).  Then since the source (and drain) are both near DC ground, when the gate of the 2n7000 transistor is raised to 9 volts the 2.2k ohm resistor is effectively shorted out.  This shorting stops the oscillator.  When the key is down the 2n7000 transistor is turned off which "unshorts" the 2.2k ohm resistor.  Keying moves the gain above the Barkhousen oscillation point.  With a capacitor on the gate the charge time decreases the gain in a shaped fashion when the key goes up.  The result is pretty decent:

1 uF cap

4.7 uF cap

2.2 uF cap

Here is the updated schematic:

As far as volume control, I am inclined to just leave the feedback pot in place and use it as a volume control.  Alternatively a series pot (probably 1k ohm or less) can be used in series with the speaker or headphones to act as a volume control.

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