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

CubuSynth Engine - Build Guide PCB V1.1 May 2022
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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.

CubuSynth Engine - Build Guide PCB V1.1 May 2022
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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

CubuSynth Engine - Build Guide PCB V1.1 May 2022
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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

CubuSynth Engine - Build Guide PCB V1.1 May 2022
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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

CubuSynth Engine - Build Guide PCB V1.1 May 2022
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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