“The fizzle loop synth came into being after mashing a couple of simple 555 projects together to make one. At the heart of the fizzle loop is a Vactrol a simple little part that is made from an LED and a photo resister such as a CdS.
Calling this a synth might be pushing it a little - it’s more a sophisticated noise maker but it’s still a lot of fun to use and play with.
The first 555 project controls a flashing LED and the second utilizes a photo resistor to change the pitch. There are multiple ways to control the sound from the synth and Im sure that you could easily add a whole bunch more if you wanted to.
So what does it sound like? Well controlling the speed of the flashing LED changes the speed of the sound while changing the pot on the photo resistor changes the pitch. The other controllers also work on changing the brightness and speed of the LED giving you some really cool sounds. There is also an output jack so you can hook-up a amplifier and really get the synth pumping.
Although this utilizes two 555 timers, they are really separate projects married together. Once you build one, you just build the other and connect them together via the vactrol. I also gave each 555 their own poer source as I was getting some noise from using a common ground for both 555 timers.
If you have never done any projects with a 555 timer, then I would suggest you make a couple of these first to get yourself familiar. This isnt a hard project but you will need some experience in how circuits are put together and to be able to read a schematic.
Lastly, I wont be going through a step by step guide on how to solder all this together. Im going to assume that you can understand the schematics and can figure it out for yourself. Ive taken some images of the important parts and added some explanations where warranted.”