4-Oscillator SynthesizerProduce and combine square waves
Amplify (Optional) Step 4 of 6
At this point, you can send your output to an external amplifier of some kind - or, build one into your system. I chose to include an LM386 op-amp in my design. Besides power (to pin 6) and ground (to pin 4), I sent all of my oscillator outputs through 1K resistors toward a common pin: Pin 3 of the LM386. That's the op-amp's noninverting input pin.
I also sent the LM386 output from pin 5, through a 1K resistor, back to pin 2. That's the inverting input pin. Finally, I connected pin 5 (output) to a 1/8" female audio jack.
You could also skip all of this and just connect your merged outputs from the CD4093BE straight to the output jack, but I wanted to try out an LM386...