CubuSynth Dual CS-20 VCF User manual

CubuSynth Dual CS-20 VCF - Build Guide PCB V1.4 Mar 2023
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Dual CS-20 VCF
Dual / Stereo Multimode VCF with Self-oscillating Resonance and
intuitive Routing and CV modulation Matrix
Build Guide
PCB V1.4 March 2023
Written and Illustrated by Ruben Sponar

CubuSynth Dual CS-20 VCF - Build Guide PCB V1.4 Mar 2023
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Introduction
The CubuSynth Dual CS-20 VCF is a dual / stereo multimode VCF / Phaser / VCO,
inspired by the legendary Korg MS-20, with CV control over frequency and resonance.
The resonance can self-oscillate and features a 1V/Oct input, stable over at least 2~3
octaves.
Each of the two filter cores has 2 stages of Low Pass and High Pass filtering, which can
be blended.
The Frequency CV can be “attenuverted”(with inverting attenuator on CV input). The
resonance CV comes with an attenuator.
This Build Guide is written for buiders with experience in soldering and assembling PCBs.
Due to the complexity of the build, the guide is focused on the steps that require special
care or techniques. Therefore, not every component value is described and listed as a
single step.
The components and quantity needed for each step are shown like this.
Quantity
Name
Designator
Tools Required
Soldering iron (+wire)
side-cutter
snipe nose plier
flat head screwdriver
Nut wrench / driver M8
Digital Multimeter
Helping (third) hand / PCB holder

CubuSynth Dual CS-20 VCF - Build Guide PCB V1.4 Mar 2023
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BUILD GUIDE
STEP 1 (Main PCB)
1N4148 Diodes
2
1N4148
D2,D1
Identify the 1N4148 diodes and put them in
place. Orientation is Important! Make sure
the line on the diodes lines up with the
stripe on the PCB silkscreen.
STEP 2 (Main PCB)
Resistors
2
10R/BEAD
L1,L2
8
220R
R70,R69,R68,R67,R4,R3,R2,R1
4
620R
R47,R46,R30,R29
4
1k
R17,R57,R48,R26
2
1k5
R54,R20
6
4k7
R79,R78,R56,R18,R88,R87
2
6k8
R50,R23
20
10k
R16,R58,R66,R65,R64,R63,R62,R60,R53,R51,R22,R13,
R11,R9,R8,R7,R6,R5,R52,R14
2
20k
R73,R72
2
33k
R49,R25
12
100k
R81,R80,R77,R76,R45,R39,R38,R31,R28,R27,R61,R10
2
470k
R55,R19
1
3M3
R86
There is different ways to go, you might already have developed your own method to place the
components and solder.
You can always select the resistors of the same value, place them, turn the board around and
solder in place. Trim the solder legs and move on to the next value.
Another method is to place all resistors and solder them from the top, without turning around
the board.

CubuSynth Dual CS-20 VCF - Build Guide PCB V1.4 Mar 2023
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Here is a picture of all resistors in place.
To help keeping track of the already placed
components, print the BOM and cross out the parts
you already soldered.
STEP 3 (Main PCB)
1N4007 Diodes
2
1N4007
D4,D3
Identify the 1N4007 diodes and put them in place.
Orientation is Important! Make sure the line on the
diodes lines up with the stripe on the PCB
silkscreen. Then solder.

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STEP 4 (Main PCB)
IC sockets
4
IC-Socket 14pin
U3,U6,U8,U9
3
IC-Socket 16pin
U5,U2,U1
Look for the dip-14 and dip-16 sockets.
Oriantation is important to know how to place the ICs later!
The place for the notch is marked on the PCB with a "D
shape", in this Picture marked red for clarification.
You can use tape to hold them in place, put the other PCB
on top or bend 2 pins of each socket inwards, so they don't
fall when turning the board around. Then solder
everything.
STEP 5 (Main PCB)
100nf ceramic capacitors
14
100n
C24,C23,C22,C21,C20,C19,C18,C17,C16,C15,C14,C13,C12,C11
Find the 100nf ceramic capacitors
They are marked as "104"
Orientation doesn't matter. Put them in place and bend the solder legs outwards, so they don't
fall when turning around the board.
Solder all of them in place. On the next page you can see the placement of the 100n capacitors

CubuSynth Dual CS-20 VCF - Build Guide PCB V1.4 Mar 2023
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STEP 6 (Main PCB)
1nf ceramic capacitors
2
1n ceramic
C5,C4
The 1nf ceramic capacitors are marked
as "102"
Place them in their spots and bend the
solder legs outwards.
Turn the board around and solder them
in place.

CubuSynth Dual CS-20 VCF - Build Guide PCB V1.4 Mar 2023
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STEP 7 (Main PCB)
4.7nf ceramic capacitors
2
4n7
C6,C3
Find the 4.7nf ceramic capacitors
They are marked as "472"
Place them as shown in the picture and solder
them from the other side of the board.
STEP 8 (Main PCB)
1nf boxed capacitors
4
1n Boxed
C2,C7,C25,C26
Place the 1nf boxed capacitors. You could use any
capacitor type with 1nf, but since those are the filtering
caps, it is recommended to use high quality boxed or
polystyrene capacitors.
Orientation doesn't matter.*
*In case you decide to use special capacitors, check its specs, it
might have Polarity. Below you can see the orientation (+/-).

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STEP 9 (Main PCB)
Transistors
6
2N3906
Q6,Q5,Q4,Q3,Q2,Q1
Take the 2N3906 transistors, put them in place and make
sure the orientation is correct. The outline of the
transistor has to match with the silkscreen on the PCB
like shown in the picture.
They will stand off the PCB by around 1-2mm. Do not try
to push them all the way down.
Then turn around the board an solder.
STEP 10 (Main PCB)
1uf Electrolytic capacitors
2
1u
C8,C1
Place the two 1uf capacitors on the PCB with the white line on the capacitor facing towards the
white mark on the PCB. The longer leg of the capacitor goes through the hole marked with "+"

CubuSynth Dual CS-20 VCF - Build Guide PCB V1.4 Mar 2023
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STEP 11 (Main PCB)
Power header
1
EURORACK10
SV1
Turn around the board and place the Pin Header for Power like shown.
Orientation of the Power Header is very important to be able to insert the power cable the
correct way.
Put some tape, to hold it in place while soldering from the other side or push it against the PCB
with your fingers while soldering the first Pin. Be careful to not touch the one Pin you are
soldering, it gets very hot!
STEP 12 (Main PCB)
10uf Electrolytic capacitors
2
10u
C10,C9
Place the two 10uf capacitors on the bottom of the
PCB, with the white/grey line on the capacitor
facing towards the white mark on the PCB. The
longer leg of the capacitor goes through the hole
marked with "+"

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STEP 13 (Main PCB)
Trimmer
2
3296W Trimmer 1k (102)
RP1_102, RP2_102
1
3296W Trimmer 100k (104)
RP3_104
Place the 100k Trimmer according to the marking on the
PCB, like shown in the picture.
You can bend the legs outwards, so it stays in place.
Turn around the board and solder.
STEP 14 (Main PCB)
M3 Standoffs /Screws & Pin Headers
3
HDR-F-2.54_1x8
J5,J3,J2
3
HDR-M-2.54_1x8
J6,J4,J1
1
M3 Spacer 11mm
2
M3 Screw Philips Head
Place the screw in the hole of the PCB and place the spacer, so it stands off on the side with all
components like in the pictue on the left.
Then put together the male and female pin headers and place them on the PCB like shown in the
picture below on the right.