A classic MS-20 VCF Clone for Eurorack, in 4HP.
This design is a classic, and many variations can be found across the internet and in many synthesizers and modules. It is based on the late Korg MS-20 VCF schematics which is a variation of the Sallen-Key 2nd-order filter.
(This variation adds a first buffer compared to the original Sallen-Key structure).
The filter can be switched from “Low Pass” to “High Pass” mode.
Documentation
Attention! This project is rather old and needs some adjustments!
External links
Other VCF based on the MS-20 filter:
- http://www.schmitzbits.de/ms20.html
- synthdiy.com wiki
- http://www.analog-synth.de/synths/mod2/ms20filter/ms20filter.htm
- http://www.ericarcher.net/wp-content/uploads/2014/07/9v-analog-diy-lpf.pdf (archived)
- http://www.timstinchcombe.co.uk/synth/MS20_study.pdf
- https://aisynthesis.com/how-to-build-ai004-diy-eurorack-ota-filter-vcf/
Hi David
Could you clarify the schematic for me – I want to make sure I’m reading it correctly. There’s three points within the circuit labelled ‘exp_out’, together with a test point; I’m assuming that these are all common (based off the similarity to René Schmitz’s design).
Hello Steve,
You’re absolutely right, ‘exp_out’ is a *label*, a way to tell KiCad things are connected, but without the need to draw a line.
It’s just a convenient way to not overcharge too much the drawings, particularly here, where the Iabc pins of the OTA are oriented toward the bottom… 🙂
Yep yep! I’m just so used to seeing and using global labels in KiCad that anything that isn’t in a ☖ or ⛉ sort of shape doesn’t register the same to me 🙂
Hi David, awesome website. I’ve made your simple vco and lfo, and now looking at this. When you say it’s old and needs adjustment, what do you have in mind? I’m assuming it’s totally fine as is for a simple build?
Hi James, thank you for your kind words.
The circuit **works** and honestly, it’s so old that I do not remember why I said that in the first place actually ^^’
I personally prefer the SVF (Formant VCF) over the MS20 VCF, but I just noticed that I forgot to publish about it here. And about the Simple VCF too!
I add this to my todo list!
Thank you! I built it on breadboard and love the sound, but I’m only using a linear pot with 20k from ground pin to wiper to ‘fake’ a log pot (until I get one). Resonance is quite intense at the top end; I’ve used one green and one red LED on the feedback bit–wondering if having two red would smooth it out a bit, if they have an impact on the sound or balance.
I’d love to see a simple VCF design too, these circuits are great. I’ll be naming my synth “The Haillant-Klein”, considering the help I’ve got from your collective posts and websites