CubuSynth Dual CS-20 VCF Dual or Stereo Multimode VCF User Guide

Dual CS-20 VCF Dual or Stereo Multimode VCF

CubuSynth Dual CS-20 VCF – Product Information

The CubuSynth Dual CS-20 VCF is a dual/stereo multimode VCF/Phaser/VCO inspired by the Korg MS-20. It features CV control over frequency and resonance, with the resonance capable of self-oscillation. 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), and the resonance CV comes with an attenuator. The product is designed for builders with experience in soldering and assembling PCBs.

CubuSynth Dual CS-20 VCF – Product Usage Instructions

• Step 1: Identify the 1N4148 diodes and put them in place. Orientation is important.
• Step 2: Identify the resistors and place them according to their corresponding value. You may choose to place them all at once or one value at a time.
• Step 3: Identify the 1N4007 diodes and put them in place. Orientation is important.
• Step 4: Look for the dip-14 and dip-16 sockets. Place them according to their corresponding ICs and make sure to take note of the orientation.

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 builders 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.

Tools Required

• Soldering iron (+wire)
• side-cutter
• snipe nose plier
• flat head screwdriver
• Nut wrench / driver M8
• Digital Multimeter
• Helping (third) hand / PCB holder

BUILD GUIDE

STEP 1 (Main PCB)
1N4148 Diodes

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

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.

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

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.

STEP 4 (Main PCB)
IC sockets

Look for the dip-14 and dip-16 sockets. Orientation 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

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.

STEP 6 (Main PCB)
1nf ceramic capacitors

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.

STEP 7 (Main PCB)
4.7nf ceramic capacitors

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

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 (+/-).

STEP 9 (Main PCB)
Transistors

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

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 “+”.

STEP 11 (Main PCB)
Power header

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

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 “+”.

STEP 13 (Main PCB)
Trimmer

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

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 picture 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.

Now place the other PCB on top, so all Pins go into their holes and fix the PCBs together with the M3 screw. Then you can solder all Pins on both sides (both PCBs) After that, you can unscrew the M3 screws/header and carefully take apart the 2 Boards.

STEP 15 (control PCB)
Resistors

Now take the other (control-) PCB, place the resistors as marked on the PCB. On the next page, you can see a picture with all the resistors in place.

STEP 16 (control PCB)
LEDs

Place the LEDs on the PCB. Orientation is Important! The longer leg goes into the square hole.
Bend the solder legs outwards so they stay in place and solder them.

STEP 17 (control PCB)
Controls

First, place fix the M3 spacer, like shown in the picture.
Now take the Potentiometers and jacks and put them in place as marked on the PCB but don’t solder yet.
In the picture below you can see the placement.
When everything is in place, take the front panel and put it on top, so all controls go into each corresponding hole of the panel. “wiggle” the front panel into place and make sure everything fits well.
Fit all nuts to the Potentiometers and the Jacks. Be careful when turning the board around, so that all the components stay in place. Then solder everything.

STEP 18
Installing ICs and final check

Take the Main PCB and install the Ics. Bend the Legs of the Ics inwards a bit so they form a 90° degree angle to the body of the chip. Make sure the orientation is correct, the notch has to match the silkscreen / the sockets placed before.

Check your soldering. If you see shorts or bad solder joints, fix it up. Then check the power pins for shorts with your multimeter.
When everything looks fine, you can connect the two boards together again, with the three Pin headers connected properly.
Then tighten the Screw on the Main PCB to the standoffs.

Step 19
Knobs
Place the knobs on the Potentiometers. For best results, turn all Potentiometers counter-clockwise and push on the knobs, so the marking points towards the left end of the surrounding circle.

Step 20 ­ Calibration

The Calibration process contains the two trimmers for the 1V/octave scaling and an Offset for the second Filters frequency to have them both on the same resonant frequency.

V/O Trim1:

1. Turn the Resonance (Q) knob all the way clockwise (100%) and both filter modes to LP (counterclockwise / 0%)

2. Plug the Output (OUT1) from the Module to an Oscilloscope or musical Tuner

3. Turn the Frequency down to 220hz (or a musical note of your choice)

4. Apply 1V to the 1V/O input (one octave on a keyboard)

5. Trim the V/O Trim1 on the Back of the module until the frequency doubles (440hz/ One octave above initial note)

6. Repeat steps 3-5 until the frequencies match ­
   V/O Trim2:

7. Plug a cable or a Jack connector to IN2 (to break connection from OUT1)

8. Repeat steps 2-6 for the Output “OUT2” and V/O Trim2
   Offset 2:

9. Plug a cable or a Jack connector to IN2 (to break connection from OUT1)

10. Connect both Outputs to a mixer and mix them with same levels

11. Turn the Trimmer “Offset 2” until the frequencies of both outputs match.

Now turn the Frequency knob and assure that the frequency of both outputs stays the same over the audible range. If not, you will notice some “swinging” or phasing between them. Go back to adjust the V/O Trimmers until they match.

This concludes the Trimming process and you can enjoy your module in perfect state.

Help

Please understand that we can’t guarantee for your DIY module to work. Nevertheless we will do our best to guide you through the build or to solve problems when needed.
In case there should be parts missing in your Full DIY kits contact us to ask for replacement / If you have trouble with your build, you can contact us at:
cubusynth@gmail.com
To be able to identify mistakes in your build, please include high quality pictures of your soldered PCBs, front + back.

https://cubusynth.com/
https://www.facebook.com/cubusynth
https://www.instagram.com/cubusynth_modular/
https://www.etsy.com/shop/CubuSynth

References

• Cubusynth- Eurorack Modular Synths & Diy Kits – CubuSynth
• CubuSynth - Etsy
• CubuSynth (@cubusynth_modular) • Instagram photos and videos

Read User Manual Online (PDF format)

Read User Manual Online (PDF format)  >>

Download This Manual (PDF format)

Download this manual  >>