Finished Pieces

Modular synth

The modular synth has been folded into a larger project called the Multi Platform Music System. You can read about it

here




This piece is an analog modular synthesizer which I’ve been working on for the past year. If you’re not familiar with what a modular synth is, click here.
MODULES:
1x 16 step CV sequencer
4x VCO
2x noise source
2x VCF
3x VCA
2x LFO
2x AR envelope
1x ADSR envelope
2x ring mod
1x Attenuated mixer
4x CV mixer/inverter

This photo shows the system (minus the bottom panel) interfaced with the step sequencer

The modules are based almost entirely on circuits designed by Paia electronics and Ray Wilson. Ray Wilson has a fantastic site called Music From Outer Space which I can’t say enough good things about. The site is an invaluable resource for the synth building enthusiast. Another good source of synth PCBs is Ken Stone’s CGS synth page. He has a larger variety of pcbs than Ray, but his documentation isn’t nearly as complete.

LAYOUT
The system is broken into three cabinets:

top- 16 step CV sequencer.
middle- modified Sound Lab Mini Synth
bottom- paia and custom modules
Below is a list of the modules with comments on each:

Details on the sequencer can be found here.
This is Ray Wilson’s design and was built using the circuit board sold through his website.
My favorite feature of the design is that the run sequence can be adjusted in a variety of ways. For instance you can set it to bounce back and forth or set it to random mode.
My only regret with this part is that I chose not to include fine tune adjustments for each step.
This makes it very difficult to program precise musical sequences. it’s still a very useful module though.

Modules from left to right:
-VCO
-VCO & Ring Modulator
-Mixer/VCF
-LFO
-LFO (main audio output module underneath LFOs)
-AR envelope generator
-VCA
-Sample and Hold

This cabinet is basically a heavily modified SoundLabMiniSynth . If you aren’t familiar with the SoundLab, you should go to Ray Wilsons site and read up on it. It’s a simple but very powerful little device and is a great project for the newbie synth builder.
What I’ve done here is take the SoundLab design and make it completely modular. There are details on his site on how to do this. Below is a list of modifications and additions.
- fine tune pitch controls for each VCO
- cross modulation switch
- ad/dc modulation switch to VCO #1
- modulation input adjustment to VCO #1
- saw and square outputs to VCO #2
- LP and BP outputs to VCF
- added 2nd LFO. Identical to the original SoundLab LFO.
- added Sample and hold module. Here’s the schematic. I highly recommend adding this circuit to your design if you build a SoundLab.
-added ring mod. Schematic.
This is an awesome and very simple ring mod. I highly HIGHLY recommend this circuit.

NOTES:
This thing is quirky all over the place. The VCAs are noisy, the filter warbles when the resonance is all the way up and the noise output only worked for a day. But overall it’s a real beast and makes some amazing sounds.
I’ve played with a few other sound labs that friends built based on the original normalized layout.
I greatly prefer the modularized design and think it allows for a lot more experimentation and potential for further developement.
If you do decide to build a modular SoundLab, I strongly recommend that you include input adjustment for many of the parameters. I wish I had installed more of these.
Sample and hold and ring mod are a must!


Modules from left to right:
-VCO
-VCO
-AR envelope generator
-ADSR envelope generator
-Dual VCA
-Ring modulator
-Noise source
-Dual 3 input CV mixers/inverters
-4 input audio/CV mixer
-VCF
-Signal attenuator
-Dual 3 input CV mixer

This cabinet is made up of modules from a Paia 9700 synth, a few simple Ray Wilson designs and a VCF using the SSM2044 IC.
Paia makes a decent modular synth that you can buy in kit form called the 9700. It’s a pretty clever design and they figured out how to cram a whole lot into a small package. The problem I have with it is that I think the normalizing scheme is a little to clever for it’s own good and it ultimately results in a confusing layout. I decided to reconfigure the layout of the VCO and VCA modules and include them in the synth. It ended up being a little more complicated than I thought it would be and I had to spend a lot of time studying the schematics. I made a few modifications as well while I was at it.

- adjusted VCOs for wider pitch range
- fine tune adjustments for both VCOs
- pulse width modulation inputs for both VCOs
- added output amount adjustment to ADSR
I had some space left on the panel, so I decided to add some signal mixing modules and a high quality VCF.
The schematics for the mixers can be found here.
The VCF is based around the SSM2044 chip. This is a sort of all in one synth chip. The module was built pretty much directly from the spec sheet.
you can read more about the SSM ic series here.

Sounds

2 Responses to “Modular synth”

  • 1

    Doc Normal said:
    January 29th, 2013 at 1:15pm #

    Regarding the sequencer (fine tune of stages..),
    have you considered a quantizer?
    The simplest is an AD and DA paired up..
    http://www.ti.com/product/adc0800
    http://www.ti.com/product/dac0800
    this gives stepped output that can be fed through a
    VCA to give a range of scales.

  • 2

    casper said:
    February 23rd, 2013 at 3:49pm #

    @Doc: Yeah I love quantizers… you can do crazy stuff by quantizing a high frequency modulation signal. Thanks for the links!

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