CubuSynth VCFA User manual

CubuSynth VCFA - Build Guide PCB V1.2 Sept 2022
VCFA
Multimode VCF with LP,HP and BP outputs and integrated VCA
Build Guide
PCB V1.2 Sept 2022
Written and Illustrated b Ruben Sponar
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CubuSynth VCFA - Build Guide PCB V1.2 Sept 2022
Introduction
The CubuSynth VCFA is a multimode VCF with P,HP and BP modes with integrated VCA,
CV control over Frequency, Resonance and Volume. The CV input for the Frequency
features 1V/Oct scaling over at least 2 octaves. So you can even create plucky melodies
with the resonance in "ringing" mode.
The Gain control can reach a nice, soft overdrive.
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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CubuSynth VCFA - Build Guide PCB V1.2 Sept 2022
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
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2 1N4148 D2,D1
2 10R L2,L1
8 620R R30,R29,R23,R20,R19,R11,R8,R7
3 1k R43,R16,R1
4 6k8 R28,R27,R13,R12
2 10k R44,R42
2 20k R18,R9
2 33k R15,R2
1 47k R41
2 68k R36,R32
11 100k R49,R40,R39,R37,R26,R25,R21,R17,R10,R6,R46
2 200k R31,R4

CubuSynth VCFA - Build Guide PCB V1.2 Sept 2022
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)
ceramic capacitors
Find the ceramic capacitors
1nf is marked as "102"
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 the placement of the 1n
(here in yellow) and the 100n capacitors.
Page 4
2 1n C10,C5
10 100n C20,C19,C14,C13,C12,C11,C4,C3,C2,C1

CubuSynth VCFA - Build Guide PCB V1.2 Sept 2022
STEP 3 (Main PCB)
220pf capacitors
Place the 220pf capacitors. You can use any capacitor type with 220pf, but since those are the
filtering caps, it is recommended to use high quality boxed capacitors.
Orientation doesn't matter.
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2 220pf C16,C15

CubuSynth VCFA - Build Guide PCB V1.2 Sept 2022
STEP 4 (Main PCB)
IC sockets
ook 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"
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)
Electrolytic capacitors
Bend the legs of the two 47uf capacitors, so they form
a 90° angle, as shown here.
Then place them on the PCB with the white line on the
capacitor facing down towards the white mark on the
PCB. The longer leg of
the capacitor goes
through the hole
marked with "+"
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3 DIP14 socket TL074
2 DIP16 socket LM13700
2 47u C7,C6

CubuSynth VCFA - Build Guide PCB V1.2 Sept 2022
STEP 6 (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 below.
Then turn around the board an solder.
STEP 7 (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.
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4 2N3906 4, 3, 2, 1
1 EURORACK10 SV1

CubuSynth VCFA - Build Guide PCB V1.2 Sept 2022
STEP 8 (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 9 (Main PCB)
M3 Standoffs & Screws
Place the screws in the holes of the PCB so they stand out on
the side with all components and screw them from the other
side like in the pictues.
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1 CV Trim TRIM1_100K
2 M3 Spacer 11mm M3 spacer 11mm height
4 M3 Screw M3 screw, max length 6mm, Philips Head

CubuSynth VCFA - Build Guide PCB V1.2 Sept 2022
STEP 10 (control PCB)
Resistors
Now take the other (control-) PCB, and place and solder the
resistors.
Here is the list of parts and a picture with all resistors in
place.
STEP 11 (Main & control PCB)
Pin headers
Take the 1x6 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!
Now take the other PCB and fit it on top, so the pins of the male headers are showing through.
Screw the PCBs together with the M3 screws, while soldering the pin headers on both sides (both
PCBs).
Then remove the screws from the Main-PCB. You can let the Standoffs fixed to the control-PCB.
The next page shows pictures of this step.
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4 1k R35,R34,R33,R47
6 100k R45,R38,R22,R5,R48,R14
2 330k R24,R3
2 HDR-F-2.54_1x6 H2,H1
2 HDR-M-2.54_1x6 J9,J7

CubuSynth VCFA - Build Guide PCB V1.2 Sept 2022
STEP 12 (control PCB)
4.7 uf capacitors
bend the legs of the Capacitors so two of them have the white
stripe on one side, and two on the other as shown here.
Place them on the PCB so the white stripe of each cap faces
outwards from the middle. The longer leg of the capacitor goes
through the hole marked with "+"
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4 4u7 C18,C17,C9,C8

CubuSynth VCFA - Build Guide PCB V1.2 Sept 2022
STEP 13 (control PCB)
Controls
Now take the Potentiometers and jacks and put them in place as
marked on the PCB but don't solder yet.
In the picture 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 boards around, so that all the
components stay in place.
Then solder everything.
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7 PJ-301M IN1,CVR1,CV1,ACV1,J3,J2,J1
3 100K FRE ,GAIN,RESO
3 100K CVA,FCV,RCV,

CubuSynth VCFA - Build Guide PCB V1.2 Sept 2022
STEP 14
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 egs 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 Pin headers are connected properly. Then tighten the
Screws on the Main PCB to the standoffs.
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3 TL074 U1,U4,U5
2 LM13700N U3,U2

CubuSynth VCFA - Build Guide PCB V1.2 Sept 2022
Step 15 - 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 16 - Trimming
Before your module is finished, you need to callibrate the trimmer on the back.
Please note, that this is a filter and not a VCO, so 1V/oct tracking will not be the most precise.
But it will be quite stable over at least 2 octaves.
First plug in the 16pin Eurorack Power cable correctly to your Busboard 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 P to the output of your rack. (speakers / headphones).
To adjust the V/oct tuning, set the resonance to 100%, then plug a Keyboard/Sequencer or MIDI-
interface, that produces 1V/oct signals to the Freq CV input (set the Freq CV knob to 100%) and
the Gate to the Input of the VCFA. This allows the resonance to "ping" at given Frequency.
Play the lowest C on the keyboard and tune the big Frequency 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 2 or 3 octaves higher.
If you prefer, you can also let a sequencer play through the octaves in 2-3 steps (C1, C2, C3...)
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 (e.g. oscilloscope), you can tune down
to exactly 100hz, the next octave should always double the frequency to 200hz, then 400hz,
800hz, 1600hz and so on.
Congratulations, you can now install the module in your rack and have fun patching!
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CubuSynth VCFA - Build Guide PCB V1.2 Sept 2022
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:
[email protected]
To be able to identify mistakes in your build, please include high quality pictures of your
soldered PCBs, front+back.
https://cubusynth.com/
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https://www.etsy.com/shop/CubuSynth
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