“What!?? Another Atari Punk Console build?
Wait wait wait people, this one is different, promise.
Waaay back in 1982, Forrest Mims, Radio Shack booklet writer and Young Earth Creationist (roll eyes emoji) published the plans to his Stepped Tone Generator. It used two 555 timer chips (or one 556 dual timer chip). One of the timers was set up to be a free running oscillator, putting out a variable frequency square wave signal. The other timer was used as an astable or “one-shot” timer, accepting a trigger and then staying “on” for a variable amount of time. When the signal from the first timer was connected to the trigger pin of the second timer, the output of the second timer would become a variable pulse width variable rate signal that would jump in frequency based on how wide the pulse width of the second timer.
Basically, you’ve got a fun little noisemaker that can put out interesting reedy tones, and the two knobs controlling the primary oscillator and the secondary timer interacting with each other in interesting, quirky ways.
“So how is this different?” you’re asking.
This one is built without a circuit board. Also, there’s two secondary timers.
Yes. Two secondary timers. Three 555 timer chips like in the picture.
What that means is the tones that the two secondary timers put out are always related to each other because of math! So you can get rock-solid polyphonic harmony out of a super basic circuit. Polyphonic harmony is hard, folks, I chased exponential-response 1 volt per octave voltage-controlled oscillators for a couple years before I got something I was satisfied with.
Right! So put on your harmonious listening hats and get ready to build some magic!
Supplies:
3 x NE555 chips. You can use any sort of 555. It’s an ancient design, so the originals are power-hungry and don’t always play nicely with other circuitry, so there’s dozens of different versions out there with modern guts, but they should all respond exactly the same in this circuit.
3 x 220R resistors
1 x 1K resistor
3 x 10uF electrolytic capacitors
1 x 10nF capacitor (ceramic disk is fine, multilayer is fine, film is fine, doesn’t matter really)
1 x 100nF capacitor (ceramic disk or film or multilayer ceramic not important)
1 x 47nF capacitor (same as the other ones, really not important)
3 x 1M potentiometers
bits of wire to hook stuff up
a power supply that can provide 9 to 12V
This build will need a mixer to blend the outputs of the two secondary timers. I’ll show two options.
3 x 1K resistors
that’s all the first mixer needs. Just three resistors.
Here’s the second, fancy mixer
1 x TL072 op amp chip
1 x 100nF capacitor (ceramic disk is actually best!)
2 x 1uF capacitors (electrolytic is fine)
3 x 10K resistors
1 x 10K potentiometer
a power supply that can provide positive AND negative voltage, 9V to 12V”