If you want to learn more about the logic math behind the flip flop, I recommend this video:
Here is a sound example of octave down with: 1. Bridge pickup, no filter 2. Bridge pickup with RC filter 3. Neck pickup with RC filter.
Let's get the breadboard ready!
We'll start out with the circuit we made in part two, then add the new section before the output capacitor. To keep it simple, the schematics will not show the "cmos'ifier" part or the output part. Lets add the RC filter first (R6/C4). 10K and 22nF-100nF is a good starting point. Then we'll add the octave down part.
No decoupling capacitor after the schmitt trigger is needed. CMOS chips are make to interface with each other directly so decoupling caps are rarley needed, except for linear amplifiers, filters or special schmitt trigger operations. It's very forgiving this way.
You can use pots/trimmers as variable resistors or voltage dividers to have control over each octave or a switch to toggle between them, a blend pot/trimmer between straight square wave and octave down ect... Experiment with the controls that you want. Here are a few examples:
It works. :) I actually used this flip flop version for the sound example in the beginning of the post. This was very confusing to breadboard and I won't even try to make a breadboard diagram. It's not a very convenient method, unless you have a huge stash of schmitt triggers and diodes that you want to put to good use... I just wanted to show you what is possible.
It can be a good idea to have a RC lowpass filter on the octave output if you want it to sound less synthy or harsh. It's common to filter out anything above around 100hz to make it blend better with a clean guitarsignal. Experiment!
I'll stop here. This post became massive and took me a whole day, and I didn't even mention octave down by using gated oscillators, phase locked loops or shift registers. Maybe more about that in a later part. But in the next part I will cover LFO's and oscillators.
We will analyze the Flawed Logic Fuzz and we will breadboard a drone synth.
UPDATED 2023-10-31: Some minor spelling fixes.