the 4093 cmos nand ic is capable of producing the same sort of oscillators as the 40106 that we covered previously, and this tutorial goes into a bit more depth as what you can do with them from the simple dual sync’d synth we made last time.
the truth table of the 4093 is as follows.
input 1 | input 2 | output
0 | 0 | 1
0 | 1 | 1
1 | 0 | 1
1 | 1 | 0
the 4093 has 4 gates with 2 inputs each. if we wire up a simple oscillator using one input (pin 2) and the corresponding output (pin 3), then we can control the on/off state of the oscillator by connecting the other input (pin 1) to v+ or ground. remember to connect the power pin 14 to v+ and pin 7 to ground.
you’ll notice a 100k resistor to ground on pin 1. this isn’t always necessary but i find in logic switching situations, (on/off, 1/0) it helps keep everything in check and clamps the input to ground to avoid any unwanted fluctuations. the output (pin 3) is connected to a 100k pot, and the following circuit gives us volume control over the output.
so that’s simple enough, but as we’ve done before, we can use another oscillator to gate one of the inputs of another oscillator, and by adding a toggle switch, we can turn the sync effect on and off by toggling the input of the second oscillator to v+ as shown. this can create some nice flanging and hard sync effects on the output of the second oscillator.
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if we tie input pin 1 to v+ then this makes our first oscillator always on, the output of which, we can use to gate the input of our second oscillator (pin 5), or use the toggle switch to connect it to v+ to turn off the gating effect, making the second oscillator always on. by incresasing C1 to 1uf, the syncing effect is slower, giving pusle’s of sound from the second oscillator.
now, if we use the remaining gates on the ic, then we can connect another 2 oscillators in series as per above, but i decided to try another method to gate the output signal. using one of the remaining gates as another oscillator with its spare input tied to v+ to make it always on, we connect the output from this (pin 11) to the input pin 8, and the output from our second oscillator to the input pin 9. again, i used 100k resistors on the 3rd gates inputs to pull down to ground to ensure nice clean signals and keep the inputs happy. we can turn the gating on and off by using a toggle switch connected to v+, in between output pin 11 and input pin 8.
the out pin of the 3rd gate (pin 10) is then routed to the volume control pot.
by tuning the 3rd oscillator, we can switch the output of the 1st and 2nd oscillator on and off. using a lower capacitor for C6 will give fast gating of the output, and tuning it up to the same sort of speed as the other oscillators will give nice flangy effects. increasing the capacitor C6 to something like 1uf will give pulse’s of sound much more slowly.
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5 minutes of knob twiddling and droning fun.
