CubuSynth Engine User manual

CubuSynth Engine - Build Guide PCB V1.1 May 2022
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Dual Complex VCO with wave shaping and modulation features
Build Guide
PCB V1.1 May 2022
Written and Illustrated by Ruben Sponar

CubuSynth Engine - Build Guide PCB V1.1 May 2022
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Introduction
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.
Tools Required
Soldering iron (+wire)
side-cutter
snipe nose plier
flat head screwdriver
Nut wrench / driver M6, M8, (M9/M10)
Digital Multimeter
Helping (third) hand / PCB holder

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MODS (optional but recommended)
Before you start, consider integrating these mods into your module. They will improve some of
its outputs significantly.
As the printing on the PCB still shows original resistor values, you should place these ones first to
minimize confusion.
WAVEFOLDER OUTPUTS:
R189, R190: change from 20k to 47K for higher Gain of wavefolder.
R236, R237: adjust for offset of wavefolder (usually 47k - 470k)
Leave them out until you Power up the finished module, then check the offset of the wavefolder
outputs on an oscilloscope with the wavefolding knobs on 100%.
If the Outputs are not centered around the 0V point, place 100k resistors and check again. Lower
Resistor values shift the output towards positive Voltages.
TRIANGLE OUTPUT:
R2, R3: change from 100k to 110k for offset of Triangle output, also improves sine roundness.
SINE OUTPUT:
R85, R92: change from 100k to 47k - 68k for better sine roundness.
Adjust R81, R96 to 220k –270k for higher amplitude
PULSE WAVE (VCO1):
C20: replace with wire (cutted resistor leg) for a straight Pulse on VCO1.

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BUILD GUIDE
STEP 1 (Switch PCB)
Take the small Switch adapter PCB and the 4 position slide switch. Place the switch on the side
that says SW3. It is recommended to use a helping hand to secure them together while soldering.
When soldered, cut the solder legs flush with the PCB to avoid shorting them later!
Then put it aside for later use.
STEP 2 (Main PCB)
Resistors
There is several ways to go, you might already have developed your own method to place
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.
On the next page, you can find the list of resistors needed for the main PCB and a picture of all
resistors in place.
To help keep track of the already placed components, you can print the BOM and cross out the
parts you already soldered.
For the "10R/Bead" you can either use Ferrite Beads or 10R resistors.

CubuSynth Engine - Build Guide PCB V1.1 May 2022
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3
10R/Bead
L2,L1,L3
1
220R
R113
4
470R
R55,R44,R26,R18
6
820R
R56,R27,R101,R68,R37,R35
19
1k
R214,R127,R126,R89,R88,R78,R67,R62,R50,R36,R16,R4,R95,R94,R83,R82,
R130,R129,R186
2
1k8
R46,R20
2
2k2
R196,R181
2
5k6
R54,R25
4
6k8
R195,R182,R61,R60
20
10k
R199,R194,R193,R192,R187,R184,R183,R178,R158,R112,R110,R64,R58,R121,
R120,R119,R118,R117,R116,R115
2
15k
R197,R180
28
20k
R205,R204,R203,R202,R201,R200,R175,R174,R173,R172,R171,R170,R66,R51,
R65,R57,R123,R109,R108,R107,R106,R105,R104,R103,R102,R190,R189,R188
2
24k
R49,R24
2
33k
R63,R59
10
47k
R198,R179,R166,R53,R30,R5,R142,R52,R237,R236
3
68k
R212,R145,R140
24
100k
R213,R146,R139,R92,R85,R77,R74,R73,R72,R71,R70,R69,R6,R111,R34,R29,
R7,R3,R2,R1,R122,R100,R75,R191
9
200k
R28,R8,R91,R90,R87,R86,R132,R96,R81
3
330k
R47,R22,R185
3
470k
R97,R93,R84
2
560k
R21,R15
6
1M
R114,R98,R48,R43,R23,R17
2
1.5M
R45,R19

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STEP 3 (Main PCB)
Diodes
Before continuing with the build, check the time! You won't believe how much time has passed
while "only" soldering the resistors. Go to sleep if it's late or make a break. It is quite unlikely
that you will build the full module in just one day.
Identify the 1N400X* and 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.
*can be any from 1N4001 to 4007 or 1N5819 (marked as 1N4007 on the PCB)
2
1N4001
D1,D2
5
1N4148
D3,D5,D4,D6,D7
STEP 4 (Main PCB)
ceramic capacitors
Find the ceramic capacitors
100pf is marked as "101"
1nf is marked as "102"
10nf is marked as "103"
100nf is 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 ceramic capacitors in place. On the next page you can see how your PCB should look
by now.
6
100pf
C53,C52,C51,C46,C45,C44
2
1n
C15,C11
4
10n
C22,C21,C9,C6
20
100n
C59,C57,C56,C55,C54,C40,C39,C38,C37,C36,C34,C27,C26,C23,C20,C17,C10,
C8,C2,C1

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CubuSynth Engine - Build Guide PCB V1.1 May 2022
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STEP 5 (Main PCB)
Transistors
Keep the 2N5457 for later, since it stands off further from the PCB. It is recommeded to start
with the 2N3904, then the 2N3906 due to the tight placement. 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. You can bend the 2 outer legs of each transistor, so they dont fall out when turning around
the board like shown below.
Lay the PCB down on a flat surface to make sure, the transistors are flush to the PCB.
The footprint for those is quite small, so stay focused and don't use too much solder to avoid
shorts.
Check your solder joints with a magnifier and/or multimeter when in doubt.
8
2N3904
Q16,Q15,Q14,Q7,Q6,Q5,Q4,Q2
8
2N3906
Q3,Q8,Q9,Q10,Q11,Q12,Q13,Q17

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STEP 6 (Main PCB)
IC sockets
Look for the dip-8, 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 as "D shape" or with a dot on pin 1. In the picture below it is marked with a pink dot.
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.
In this image, you can see the method of using the "control
PCB" to hold the IC sockets in place while turning around the
board.
5
IC Socket 16pin
8
IC Socket 14pin
1
IC Socket 8pin

CubuSynth Engine - Build Guide PCB V1.1 May 2022
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STEP 7 (Main PCB)
Polystyrene Capacitor
Place the Polystyrene (or other high quality) capacitors.
If it has a polarization, the marking on the capacitor should point towards the white line on the
PCB.
A normal ceramic cap will work as well, but since it may affect the stability of the VCO cores,
you should use high quality Plastic Film capacitors. Make sure, they are not taller than 10mm.
Here is different types of
polystyrene capacitors
STEP 8 (Main PCB)
2N5457 Transistor
Place and solder the 2N5457 N-channel JFET.
Make sure the outline of the transistor matches with the silkscreen on the PCB.
1
2N5457
Q1
2
1n Polystyrene
C13,C5

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STEP 9 (Main PCB)
Pin headers
Turn around the board and place the Pin Headers for Power and the Expander like shown below.
Orientation of the 16 Pin Power Header is very important to be able to insert the power cable
the correct way.
Put some tape, to hold them in place while soldering from the other side.
1
Eurorack Power 16 Pin IDC
U5
1
HDR-M-2.54_2x5
H3
STEP 10 (Main PCB)
Electrolytic capacitors
Place the 3 47uf capacitors as shown below. The white line on the capacitor has to face down
towards the white mark on the PCB. The longer leg of the capacitor goes through the hole
marked with "+"
3
47u
C43,C4,C3

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STEP 11 (Main PCB)
Trimmers
Place the 6 Trimmers according to the marking on the PCB, like shown in the picture below.
2
V/O trim
TRIM2_10K,TRIM4_10K
2
Hftrim
TRIM1_20K,TRIM3_20K
2
SineSymmetry
TRIM5_100K,TRIM6_100K
STEP 12 (Main PCB)
Toggle Switches /
Pin headers
Place the toggle switches in the correct spots. The On/Off/On (3position) is the leftmost one.
Don't solder yet!
1
MINI TOGGLE On/Off/On
SYNC2
2
MINI TOGGLE On/On
SYNC1,1V/O_LINK
Take the 2x10 and 1x15 Pin Headers (Male) and Sockets (Female) and put them together. Place
them on the Main PCB, with the female header down, but don't solder yet!
On the next page you can see the correct placement of the switches and the pin headers.
2
HDR-F-2.54_1x10
H6,H5
2
HDR-F-2.54_1x15
H2,H1

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STEP 13
Control PCB
Now take the other PCB and fit it on top, so the shafts of the switches go in their holes and all
pins of the male headers are showing through. Fit the nuts to the switches and carefully turn the
board around. Solder the Switches first, they will hold together the 2 PCBs while soldering the
pin headers on both sides (both PCBs).

CubuSynth Engine - Build Guide PCB V1.1 May 2022
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STEP 14 (control PCB)
Resistors
After removing the nuts on the switches and carefully taking apart the two PCBs, place and
solder the resistors on the control PCB.
Here is the list of parts and a picture with all resistors in place.
1
220R
R206
9
1k
R215,R216,R124,R211,R209,R169,R168,R152,R150
5
2k2
R79,R80,R210,R208,R207
3
4k7
R131,R133,R99
2
10k
R151,R149
8
20k
R165,R164,R163,R162,R161,R160,R159,R134
2
33k
R148,R76
2
47k
R157,R156
10
100k
R42,R39,R38,R32,R14,R11,R10,R9,R41,R13
4
330k
R128,R125,R33,R31
2
3.3M
R40,R12

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STEP 15 (control PCB)
1 nf capacitors
place the 1n capacitors, marked as "102" and solder in place.
As shown below, the footprint also allows the placement of 0805 SMD capacitors. The DIY kits
come with normal thru-hole components.
2
1n
C18,C7
STEP 16 (Switch PCB)
Male pin headers
Place the 1x6 Male pin headers on the Control PCB, with the longer pins facing down. Then fit
the Switch with its adapter PCB on top, like shown below. Solder from top (the side of the
switch) but wait with soldering the other side.
Make sure the 2x10 pin header is soldered properly to the other side!
It will be hidden and impossible to reach after soldering the Switch-PCB.
2
HDR-M-2.54_1x6
J28,J31

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STEP 17 (control PCB)
Controls
Now take the Potentiometers, jacks, switches and the LEDs and put them in place as marked on
the PCB but don't solder yet. The Potentiometers are for "Tune", "PW" and "Ch-Att" (Chaos
attenuverter). The rest are Tall Trimmer Pots.
For the LEDs, orientation is important! The longer leg goes in the upper hole, while the flat side
of the LED points down.
Below you can see the placement for the Potentiometers. (Mirror for the other side)
Before placing the rotary switches, cut the anti-rotation pin like shown below.
The solder pins may be bent a bit due to transportation. Make sure they stand off straight when
placing on the PCB.

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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. Since it is over 40 parts that need to fit, "wiggle" the front
panel into place and make sure everything fits well.
Fit all nuts to the Potentiometers and Rotary switches. It is also recommended to fit all nuts to
the Jacks, so they are perfectly placed. You can also just slightly push them down, when the
boards are upside down, so they lay flat on the front panel.
Be careful when turning the boards around, so that the components stay in place.
The slide switch should lay down on the front panel too, like shown in the picture below.
Only solder 1 leg of each LED! It is quite difficult to solder them nice and straight. So after you
soldered all Potentiometers, Switches, Jacks and 1 Leg of the LEDs, remove the front panel
again and bend all LEDs, so they form a nice 90° degree angle to the PCB.
Then solder the remaining pins.

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STEP 18
Installing ICs and final check
Take the Main PCB and install the ICs. Make sure to install the chips in their specific spot. 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 fit the control PCB, so the switches go through their holes
and all the Pin headers are connected properly. Then tighten the Nuts for the switches on top.
Then You can fit the Front panel on top again. Fit all the nuts on the Potentiometers, Rotary
switches and Jacks.
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.

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Step 19 - Trimming
Before your module is finished, you need to calibrate the trimmers on the back.
To do so, plug in the 16pin Eurorack Power cable correctly to your Bus board and the Module
while your rack is powered OFF! Make sure orientation is correct. (Red stripe to the -12V side).
Then turn on your case and plug the VCO1 sine wave to the output of your rack. (speakers /
headphones).
The Sine wave will not show an exact sine, it will be slightly triangle shaped. Adjust the "Sine
Symmetry" so the wave looks the same on top and bottom ends, and swing around 0V.
It may show values between -5V to +5V and -5,5V to +5,5V.
(achieve better results by implementing the mods)
To adjust the V/oct tuning, plug a Keyboard/Sequencer or MIDI-interface, that produces 1V/oct
signals to the 1V/O input of VCO1. Play the lowest C and tune VCO1 to play a C. Then press the
C1 on your keyboard (one octave higher) and adjust the trimmer (without detuning on the Front)
so the tuning is exactly note C, one octave higher. Repeat those steps until the VCO always plays
a C when you play a C on the keyboard, and up to 10 octaves higher.
Repeat everything for VCO2.
If you prefer, you can also let a sequencer play through 4 octaves in 4 steps (C1, C2, C3, C4) and
turn the trimmer, until the tuner always shows the same note in different octaves.
If you don't have a tuning device, but a frequency counter (on the oscilloscope), you can replace
the notes with Hz. Tune down to exactly 100hz, the next octave should always double the
frequency to 200hz, then 400hz, 800hz, 1600hz and so on.
The HF trim might need to be adjusted. If by playing in higher frequencies (higher octaves) the
V/O tracking is not exact, turn up or down the trimmer, until the high octaves are also stable in
pitch.

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Congratulations, you can now install the module in your rack and have fun patching!
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:
[email protected]
(or the websites contact form)
To be able to identify mistakes in your build, please include quality pictures of your soldered
PCBs, front and back side.
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