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Help With Audio Oscillator Transistor Switch

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gign0894

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I have this oscillator built up as shown in the attached schematic, it is a wein bridge type oscillator. I have new requirements on how I should switch it, the previous switch utilized a low side driver driven from a microcontroller which controlled the switch, along with added components for system self checking. Now all I have to do is switch the oscillator via a 3.3V signal from a GPIO pin on the microcontroller. When the microcontroller pin is switched high I need sound to be produced from my circuit. I have tried a PNP transistor(2N4403) with no luck, I got a square wave as the output using different resistor values (100k on collector and 47k on emitter and 10k on base). This circuit does not need to be switched in the same way but I cannot switch the power/ground of the comparator IC since it runs 2 different tones for me. I also do not want to switch the output since I could get a pop sound from my amplifier before going to my speakers. Any help would be appreciated and I can use any transistor/technique!
 

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MikeMl

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Most Helpful Member
It seems to me that changing the bias on the inverting input of the opamp while keying the oscillator on/off is likely to put an audible "click" into the audio, too.
 

unclejed613

Well-Known Member
Most Helpful Member
use a MOSFET. if you feed the oscillator output through a cap, then through another cap to the amplifier, you now have a section between the caps where you can add a MOSFET. use a MOSFET with a low turn on voltage/ the drain goes to the junction between the caps, the source goes to ground, and the gate goes to your logic line. a logic high mutes the oscillator.
 

gign0894

New Member
But I need a logic high to unmute the signal... any suggestions on which MOSFET to use for this? PMOS? The output signal is around 4.6 V, same with the existing switch voltage off of pin 2.
 
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