user Visual Communications

city Dogstar Digital, LLC

  • Transistor Alternator

  • Created: Feb 04, 2017

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This is a simple circuit designed to enable switching between two different transistors in an audio gain stage with a DPDT switch.


The above schematic uses a generic common emitter amplifier configuration with the component values left blank. Capacitors and Resistors can be selected by the user to suit the specific project, and this will work just as well for a clipping distortion gain stage.

The switching method alone can be implemented during the design process so that you may A/B the results without having to manually change transistors, thus giving a more immediate comparison. You might also use this setup as part of a project's design, allowing the end user the opportunity to have two different "sound" options within the same channel of an audio device or effect (the original plan for this circuit).

To calculate your resistor values:
Transistor Bias = V * R2 / (R1 + R2)
Voltage Gain = -R3 / R4

The Capacitors isolate the DC voltage present within the amplifier, but also act as filters, so selection should be made to best suit the intended audio range.

When breadboarding a design, I use the formula:
Filter Frequency = Unplug one and try another.

I honestly have not mastered the calculations for such capacitor use, so this works for me.



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