SesquiAPC Atari Punk Console “mod”

This is an idea that I vlogged about approximately a million years ago. I finally built one into a more permanent enclosure.

(Sesqui means one and a half.)

I used something called “dead bug” construction. This refers to gluing components upside down to a surface with their legs in the air, then soldering directly to the legs without a circuit board. It’s kind of like a really crappy quick-and-dirty version of point-to-point wiring, except it lets you use more modern package types that aren’t intended for that.

I made a video demo last night. I currently lack a decent audio interface for recording. Please just bear with the static and crackles:

Here’s a rough schematic. I had to make it from memory… there are probably quite a few differences between it and the one in the video. All of the crossfade resistors are encased in heat-shrink stuck directly to the pot’s legs, for instance. And I can’t read the values on these caps without a magnifying glass, so I just didn’t.


Basically, the top 1/3 of the circuit is a narrow pulse oscillator. The first capacitor charges through R1 and R2. When it reaches 2/3 of the supply voltage, the 555 does its magic and lets the capacitor discharge through just R2 until it reaches 1/3 of the supply voltage, then the process starts over.

Every time this happens, a pulse is generated on the “OUT” pin. This pin is connected directly to the “trigger” pin on the 2nd and 3rd 555. These are set up to only let only one cycle occur every time they’re triggered. However, if they get triggered twice (or more) before the the capacitor finishes charging, then they still only output one pulse for all of the triggers that happened in that time.

Basically this means that if the first part is generating a 600Hz pulse wave, the second part is capable of outputting a wave at 600Hz, or 300Hz, or 200Hz, or 150Hz, etc. And the third part does the same thing, but these two frequencies are selected separately, which means that musically useful harmonies can made between them.

The original only has one of these dividing stages. I see a lot of people building TWO of the original in one box together, but it is my opinion that what I’ve done is about 50x as musically interesting and useful as that, and also has less parts.

If you think this sounds interesting enough to make your own, I could try going a little bit more in depth with a how-to. The original APC is one of the simplest things you can build that has a really impressive sound, and my SesquiAPC isn’t that much more involved.


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