My stripboard KS-20 filter clone

Jan 03, 2022
edited: Nov 06, 2023

My modular synth has been in need of a filter for a long time now and a MS-20 VCF clone is an obvious choice loved by many, which is no suprise as it does sound absolutely amazing. However I didn’t find a good stripboard layout online that would fit on the 24-row boards I use so I decided to design my own.

I started out by building René Schmitz’s popular MS-20 clone on a breadboard just to get a better understanding of the circuit and to see that it works. Then I stumbled upon the KS-20 by Kassutronics, which has an added circuit to blend between the low- and highpass modes as well as a drive knob for the input. I added Kassu’s additions to my breadboard circuit, tested them and started working on a stripboard layout in DIYLC.

You can find Kassu’s schematics here.

Stripboard layout

KS-20 stripboard layout

BOM

Part	Value
R8, R9, R10, R11	220
R24	1k
R22	1k5
R13	2k
R3, R20	4k7
R1, R2, R5, R6, R7, R17	10k
R14	47k
R4, R12, R15, R16, R18, R19	100k
R21	220k
R23	470k
C1, C2	1n
C10	4n7
C5, C6, C8	100n
C3	470n
C4, C9	10μ
D1, D2	LED
Q1, Q2	2N3906
U1	LM13700
U2	TL072
U3	TL074
RV1, RV2, RV3, RV4	100k lin
RV5	10k lin
RV6	1k

The changes I made to Kassu’s design:

Used 2N3906 transistors instead of BC557Cs
Replaced the 2 TL072s with a single TL074
Replaced the NE5532 (U2) with a TL072
- The TL072 can get locked up when driven too hard but I haven’t had any issues with it yet. If you build one and have issues try replacing it with another dual opamp like NE5532 or LM358.
Replaced R13 with a 2K to get more resonance
Used purple LEDs instead of green ones
- The purple ones have a bigger forward voltage than green ones so they do alter the sound a bit. I tested a bunch of different LEDs and the difference in sound between them was noticeable but very small.

Panel

Here’s the template I used to make the panel: ks20-panel.pdf (0.0 MiB)

Timelapse video of building the module

I took a bunch of pictures with my phone while soldering the module, lined them up in GIMP and converted them to a video with FFmpeg. I think it looks pretty cool.

The finished module

Frontside

The 14hp panel I made is pretty chonky and the module could have probably fit into 10hp but it looks nice and it’s good to have a bit of space for my fingers.

Backside