I had an idea the other day and I couldn’t decide if it was good or not so I just built it to find out.
Eight oscillators, an on-button and a pitch knob for each. First you adjust the pitch of each oscillator so they’re vaguely in tune with each other. Then you flick on the sequencer. Then you play polyphonic chiptunes.
So here’s what’s under the hood.
The block on the bottom left generates the clock signal that sets the tempo. C1 & R6 set the clock rate (R1 limits the maximum frequency so you can’t burn out the chip). With that clock signal being fed into the 4017, outputs Q0 to Q7 momentarily go high one after another.
The subcircuit denoted by the circle outline is repeated 8 times. It includes the indicator LED, mode switch S1, pushbutton S2, and oscillator for each of the 8 steps. The oscillator is only on so long as pin 1 is high. This high pulse can come either from the 4017 outputs, or from the pushbutton.
The outputs of all 8 oscillators are tied together via 100K resistors (R5), which is a very lofi way of keeping them buffered from each other. From there the output module is up to you. The simplest thing to do is have R7 set to about 1k – this will drive headphones directly but I can’t quite guarantee that’s a good idea. I used my rudimentary knowledge of opamps to make it more closely resemble a line-level output. In my box I also included a little amplifier module I had lying around so it makes good loud noise on its own.
As always, this circuit is pretty basic, but depends on hundreds of little assumptions – so if you have any questions feel free to ask and I’ll try to point you in the right direction.
Here’s a more complete schematic and board layout. Now there’s no excuse not to build your own!
Kequencer 2.0, now even tastier