PMFoundations Dual VCA User manual

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Dual VCA v1.2 –Assembly Guide
Thank you for purchasing this module! This is a reasonably simple build with a small number of
components.
The module is designed and sized for Eurorack systems. You will need a 16-10 pin eurorack power
ribbon connector with –12/0/+12 which is connected to a synth power supply.
Follow the parts lists, these instructions and the PCB silkscreen text to build the module.
The module consists of 1 PCB board and a front panel.
There are components installed on BOTH sides of the boards. Please ensure that you place the
components on the correct side. When referring to the TOP of a board we mean the side with the
pmF logo. The BOTTOM has no logo.
You may need to clean up the board edges with wire cutters and/or a file to remove the remains of
the tabs from the fabrication process. This is particularly important for the edges containing the
jacks. These edges will need to mate flush with the front panel.
You must follow the order of assembly as described below since some components will be soldered
underneath other components.
Constructing the board
1. Clean board edges with wire cutters and/or file to remove the manufacturing tabs.

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2. Range adjustment resistors
Using the included R10/R26 (75k) resistors, the VCA shuts off when the initial gain panel control
is just above 0. If you prefer a VCA which shuts off completely at just below the mid point of the
panel control, install wire links in place of R10 and R26. This is often necessary to combat offset
errors in some other manufacturers' envelope generators. You can also install other values for
R10/R26 (between 0 and 100k) to customize the range of the VCA further.
Install the two resistors R10 and R26 or the wire links in the positions for R10 and R26 on the
TOP of the board. Solder and clip the leads.
3. Remaining Resistors
Install the resistors on the TOP of the board. Solder and clip the leads.
4. Diodes
Install the diodes on the TOP of the board. These are polarized components. Align the stripe on
the diode with the stripe marked on the board. Solder and clip the leads.

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5. IC Sockets
Install the sockets on the TOP of the board. Observe the notch or mark on the sockets and align
with the notch or mark on the board. Solder.

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6. Power socket
Install the 10 pin power socket on the TOP of the board. The opening in the right angle socket
should face OUT from the board as shown in the photo. Solder.
7. Ceramic/film
Install the ceramic/film capacitors on the TOP of the board. Solder and clip the leads.
8. Electrolytic capacitors
Install these on the TOP. Make sure you orient these capacitors correctly. The longer lead
and/or the lead marked with a + needs to be inserted into the hole that has the “+” marking
near it. Leads marked with “-“ go in the board hole WITHOUT the “+”. Solder and clip the leads.

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9. Transistors
Install the transistors on the TOP of the board. These are polarized components. Align the
outline with the outline on the board. Solder and clip the leads.

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10. Trimmer resistors
Now populate the trimmer pots on the TOP of the PCB. Make sure they are oriented so that the
screw is above the circle on the silk screen.
11. Potentiometers
If the pots have positioning lugs on the front, cut these off with a sharp pair of flush cutting
pliers. The front of the pot (where the shaft prtrudes) needs to be flat.
Install pots on the BOTTOM of the board. Tack one pin only with solder. These will be finalized
later. Please ensure they are on the CORRECT SIDE OF THE BOARD. See Photo. There is a
"other side" marking to help remind you.

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12. 3.5mm Jack Sockets
Install SOME jacks on the top and SOME on the BOTTOM. Tack one pin only with solder. These
will be finalized later. Please ensure they are on the CORRECT SIDE OF THE BOARD. See Photo.
13. Alignment
1. Place a washer over each pot shaft.
2. Place the front panel over the board so that the pots and 3.5mm jacks align with the holes in
the panel.
3. Put nuts on the jacks and pots and FULLY TIGTEN all of them. Do not overtighten!
4. Now fully solder as many pins as you can reach of each jack and pot.

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5. Remove the front panel and solder all the remaining pins on the jacks and pots.
14. Do not install the ICs until the voltage tests are complete.
15. If you do not trust all your soldering and connections, carry out the voltage tests below before
installing the ICs

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Voltage tests
1. You do not have to do these tests if you are completely happy with your soldering and are sure
there are no bridges or incorrectly placed components. However, these tests will ensure that
the correct power supplies are sent to the IC pins to ensure they will not be damaged on power
up.
2. Plug in the power supply and connect the –VE probe of a multimeter (set to the 20V DC range)
to one of the GROUND pins of the jacks. The GROUND pin is nearest to the edge of the board.
3. Check the voltage at the following points on the board:
a. At IC1 pin 11 approx = +12V
b. At IC1 pin 6 approx = -12V
c. At IC2 pin 4 approx = +12V
d. At IC2 pin 11 approx = -12V
e. At IC2 pin 3, 5, 10, 12 = 0V
f. You should see a voltage change between ~0 and ~6V on pin 2 as you turn the "A" gain
panel control. Likewise for pin 9 and the "B" panel control.
4. If any of these tests fail to match the readings given, you should check the components and
soldering before progressing
Final Assembly
1. Place the ICs in place by aligning the notch with the notch graphic on the PCB Silk Screen and
notch on the sockets.
2. Place a washer over each pot shaft.
3. Place the front panel over the board so that the pots and 3.5mm jacks align with the holes in the
panel.
4. Put nuts on the pots and jacks and fully tighten.
5. Install the knobs.
6. NOW READ THE USER GUIDE.