@WooDWorkeR asked me to join the Drehkommando meetup at c-base and since I also had to bring him some goodies from the Chaos Communication Congress, I couldn't say no :D https://twitter.com/woodworker/status/1084192948718370816 we were able to add zynthia 2.0 to the pile of wires and noise gadgets and it didn't sound too bad. Especially when played loud ;)
But I noticed some issues that I wanted to work on later. I had no control over volume at all, something I was able to fix with a variable resistor used as a voltage divider on the output. I also had a lot of high pitched noise on the output, something that I wanted to tackle with a High Pass filter. Yes, you've read that right - I was stupid until I noticed I need a Low _PASS_ filter instead :D
I then combined it with a simple dc-offset filter - there's also a High Pass filter in the schematics taken from stackexchange.
Followed by a fixed Low Pass filter and previously mentioned volume knob. You can see spot the two signals here, yellow is coming directly from the 40106, blue is after the filter, but before the volume potentiometer.
Some slight changes to the capacitor values allow the sequencer to run a bit slower. The synced pitch mode now has a wider range of frequencies. The tone range of the knobs is now deeper.
With the pink board I also fixed the direction of the potentiometers, when you now turn them clockwise, the tones go up.
it might make sense to add an external clock input as well, but I want to make sure that any voltages are safe for the trigger level.