Friday, 25 November 2016

First DIY Synth

One of my most recent endeavours was in the world of synthesizers. As of today I've made a pretty interesting and unique little oscillator. 
I must admit, the enclosure is not the the prettiest, however it does get the job done as I needed to put this thing in a box quickly for an upcoming gig. 

The schematic was from this one youtube video (

I made a few modification to the circuit. First off I made two independent oscillators make it sound even fatter. The circuit has one main square wave oscillator. Underneath it is a Low Frequency Oscillator, same circuit as the main oscillator except at a lower frequency. This controls the Pulse Width Modulation or PWM for short. In the original schematic, the frequency was fixed. This means the LFO was only oscillating at one rate. Wanting to experiment I figured it would be really cool, and easy enough, to add a pot to be able to change the rate. Of course this added a new dimension to the sound and I'm super glad I did this cause it just adds to the versatility.  

I also realized that this is a resistance based oscillator, as opposed to the classic control voltage which is a standard amongst synths. Being resistance based, I figured anything with a resistance could control the pitch of the oscillator, even sweaty palms! This lead me to the crazy idea of somehow integrating this synth is a new and exciting way. But first here are some pics of the inside:

 Not my cleanest work but it needed to get done. Still solid though, nothing has gone wrong...yet...

 Yes! Those are key switches! Why not have some fun, am I right?
Being resistance based, I decided to put three pots in series to control the pitch. The range knob is a broad pitch and the fine is very minute, for tuning the two oscillators to each other. Onboard there is the main pitch control with the fancy silver knob. Below that knob is a switch which switches between the red trigger button or the key switch.

Here is the the patch work for the oscillators. The output is exactly as it says, the output. But the input, which was probably mal name, is a TRS jack. With a flip of the switch, the circuit get rerouted to this jack. So instead of the circuit going to the Pitch pot, it goes out through the Ring part of the TRS to one end of a resisting source, then back to the tip. So the input jack is really just a external pitch control. Now you might ask what it is that I'm using to external control the pitch? Great question!!

Being a Rush fan, I've always like the idea of bass pedals. To be able to trigger a bass synth with my feet is both a dream and very useful in a band situation. One problem was actually getting bas pedals. If you search on Kijiji, someone somewhere will be giving away an organ for free, guaranteed! My dad and I pick up this organ and promptly take it apart for it's pedals. The mechanism is quite simple:
Press down on the pedal and it will close the circuit. Now all I had to do was wire up a trim pot to pedal so they can each have different pitches.
So the signal flow now goes out of the synth, into the trim pot, then is switched on my pressing down a pedal. Then the closed circuit is sent back to the synth. All and All this is just one big resistor. 

 This only works if you have a TRS as it needs to have have an in and out.

Add a nice wooden frame and you're golden! The plexiglass, salvaged from the organ, made a nice cover for the trim pots. If ever I want to re tune the pedals, I just have to readjust the trimpots. I also have the range and fine pitch control which is in series with the 'input' jack. Having this means I can change the pitch of the pedals if I so choose. 

It has been a while since I built this, so I'm missing all the little intricacies and problems I had to fix during the construction process. A fair amount of time was spent on the breadboard for this one though. The goal was for sure to make bass pedals as well as an independent synth. So I had to really figure out how I would route everything. 

Well thank you for taking the time and perusing my latest project. I know it isn't a guitar pedal, but I had a great deal of fun and this is something that I think really interests me at the moment. 

Feel free to ask me any questions as I'd love to help!

As always, happy soldering!!


  1. DIY Guitar project is amazing experience for me and I got lot of information regarding it from here. prototype pcb assembly

  2. Where in the schematic did you put the pots, for the pitch?

    1. The top left of the schematic under the text that says: "Adjust to desired scale"

      The switches are the keyboard keys!

  3. Do you have your modded schematic?
    I've built this, and I'm trying to do the pwm mod, as well as the dual oscillator. I've built many pedals, this is my first at a synth. Cheers

  4. I got the pwm mod. Change the 470I resistor for a pot.
    I still can't work out how the oscillators connect though.