Before we start, here’s the schematic for version 1.4 from the last blog post.
Now, when I decided to change the BOSS OC2 experiment to an octave overdrive called sausage fingers and make the rotund robot a separate full on CMOS octave fuzz project, I planned on ditching the original synth mod that got me so excited in the first place. I tried it out, but it was a bit too messy. BUT, there was one option that I hadn’t tried.
During my research I read about a mod by a Danish bass player and tinkerer called Skrogh in the Talk Bass forum. For simplicity’s sake, I’ve copied Skrogh’s pictures (see below) from that post.
And in Skrogh’s own words (taken from the same Talk Bass forum post):
How it works:
–The problem with bleeding occurred (to some), because a wire with a very hot signal, with lots of overtones, was passing physically close to the clean octave.
–This mod uses the phase inverter. Instead of “flipping” (phase-inverting) the clean signal around the bias voltage, a fixed voltage is flipped – thus a squarewave is outputted.
–The OCT-1 squarewave is routed through the filter, this would need bypass, if one wants extra face-melting sounds.
–The OCT-2 automatically becomes “synthed”, but not with a squarewave.
–Each peak of the incoming signal is compared to a threshold. If the limit isn’t reached, no sound leaves the box.
–The OC-2 tracks pitch on the rising peak. The gater on the falling. This makes it possible to gate instantly.
–There is one drawback: I had to make a little workaround, so unfortunately it gates a bit harder on higher pitches.
It’s really simple, and sounded interesting enough, so I thought I’d try it out. Here’s how it sounds!
I’d already started doing the PCB layout at this point, but for the sake of adding one pot, one switch and one resistor, I thought it was worth including. If for whatever reason I change my mind, I can always leave out those components and jumper the switch. You can read all about that in the next post.
I should also mention that I intend to see what else I can do with this mod in version 2. It’s great as is, but I feel like there’s a little more in it, and I don’t intend to pinch someone else’s work without adding to it in some way. Anyway here’s the current schematic.
Next time, we’ll have a look at designing the PCB.