Thank you for purchasing the MST VCO Eurorack module kit!  This is a very advanced build.  If you feel like you can handle it, please proceed!  If not, get some help from a friend with experience or purchase a fully completed unit.

ATTN:  Please follow the BOM and these instructions and don’t populate from the PCB or these instruction pictures alone. Also sometimes we cannot get the exact pictured components, so please look over your parts and check the codes first.

The MST VCO has some components that are temperature sensitive, so it is recommended to keep your soldering iron at or under 700*F.

Lets begin!

Trimmer Potentiometers

First up are the trimmer potentiometers on the main board. Insert the trimmers into their spots as shown above, and then flip your board over onto a hard, flat surface, and solder them in place.

Resistors

It is recommended to split the resistors into two groups when populating them, so that it is easier to solder them all in place.

DO NOT Populate the Tempco Resistor yet (TC1). This resistor needs to be populated later in the build.

Insert each resistor into its designated spot, as per the Bill of Materials.

After populating the first group of resistors, flip your board over, solder them and clip the leads.

Next up, do the same thing for the second group of resistors. Then flip, solder, and clip your leads.

On the BOM, you will notice there are a couple resistors that denote they are on the Control Panel. Go ahead and populate them as well.

 

Diodes

Next up are the Diodes. Diodes are polarized components, and must be installed with the proper orientation for them to function. When inserting them through the PCB, ensure that the black stripe on the diode matches the direction of the white stripe on the PCB’s silkscreen. Make sure to put the zener diodes (DZ1 and DZ2) in their proper places.

2 Pin Header

Now would be a good time to populate the 2 Pin Header on the back of the board. Simply insert the header into the holes marked TP1 and GND, then flip over and solder it in place, making sure it is straight.

IC Sockets

The MST VCO has one IC that does NOT use a socket. Do not populate a socket into the U4 position.

When inserting the IC sockets into their respective homes, pay attention to the alignment notch on one end of the socket. It’ll look like a little half circle that was taken out. Match this alignment notch up with the one on the silkscreen so that it is easier to align your ICs later, when the are populated.

Capacitors

Now insert the capacitors into their respective spots, as per the BOM. With the ceramic capacitors, you may need to slightly bend the leads to get them to stay in when you go to solder them down.

The Electrolytic Capacitors are polarized components, and need to be installed properly. Align the longer lead (Anode) of the capacitor with the little + sign on the PCB. If they are improperly installed, it may damage the circuit, and could cause other components to fail.

Polystyrene Capacitor

Next up is the Polystyrene Capacitor. This component is VERY temperature sensative, and it is best to try to solder it without holding the iron on the leads for too long. You could even solder one leg, then let it cool, and solder the other leg.

First, we need to bend the leads so that it will fit into the PCB properly.

If you bend the leads of the Polystyrene capacitor like the picture shown above, it will be easier to populate, and ultimately easier to solder.

This capacitor is non-polarized, so it doesn’t matter which way you place it into the PCB, but it is easiest to insert it into the farther apart set of solder pads.

Transistors

Next up are the transistors. Insert them into the PCB, aligning the flat side of each transistor with the flat side that is also on the silkscreen. Then flip your project over and solder, clipping any excess leads.

Transistor Array Chip

Insert the that340-P14 chip into U4, aligning the half circle notch on it with the same notch on the silkscreen. When it is snugly against the PCB, flip your board over and solder it into place.

Tempco Resistor

Before populating the tempco resistor, place a little dab of thermal paste onto the chip in U4 (that340P14). You can also use thermal tape (if you bought a kit from us, it’s the little blue square in a bag).

Next, place the tempco resistor into the two solder pads that are just outside of pins 2 and 13 of chip U4. Make sure that the tempco resistor is sitting snug in the thermal paste or tape as shown below. Then flip your project over and solder it in place.

IC Placement

Next, insert the ICs into their respective sockets, making sure to align the notch in each IC with its socket, and the silkscreen below it as well.

 

16 Pin Shrouded Box Header

Flip the board over, so that the trim pots are facing up now. Insert the 16 Pin header into the PCB, making sure to align the notch in the header with the notch marking on the silkscreen, as shown below. Then flip the board back over and solder it into place, making sure that is snug to the PCB.

 

5 Pin Board to Board Headers

The easiest way to get the 5 pin headers and sockets into their spots, is to first assemble everything, and then solder them into place. First up, connect each header to a socket, with the longer part of the header going into the socket, like shown above.

Next, insert each header assembly into the main board, as shown below.

Now you can place the control board over the top of it, aligning the solder pads for the sockets up, so that the pins of the sockets poke through the control board PCB.

Next up, solder one pin of each header assembly on each side of the board, making sure that the boards are nice and flat, and everything is as straight as possible. If something gets a little crooked, or mis-aligned, just reheat the solder joint nearest the error, and straighten it out.

Once everything is straight, finish soldering all the headers and sockets into the PCBs. Carefully pull the boards back apart.

V/O Trimmer

Next up, insert the trimmer potentiometer into the designated place on the PCB, making sure to align the adjustment screw with the silkscreen representation of it. The side with the adjustment screw should be facing the top of the board, as shown above.

Now flip the board over, and solder it in place, clipping any excess leads. When soldering, make sure that the trim pot is fully flush with the board, or it won’t line up properly with the front panel.

Standoffs

Insert the screws for the standoffs through the PCB, and tighten them down to the standoffs, as shown above.

Jacks, Switches and Potentiometers

 

Now PLACE (do not solder yet!) the jacks, potentiometers, and switches in the PCB as shown below. Make sure to remove ALL the nuts and washers from your switches before panel placement.

Please read through the whole process before starting!

Now place the Front panel over the pots, jacks and switches.

Make sure that the 1V/O trimmer is aligned with the hole in the front panel during this part. If it is not, try to GENTLY align it with your fingers, or a tool. If it is off by a lot, it may be necessary to reheat the solder and adjust it while the solder is loose.

Use a tool to gently tighten the nuts and washers on the hardware. Be careful not to over-tighten the nuts.

Now that your components are tightened, flip it over and solder the back side of the control board.

Final Assembly

Next, line up the two boards, so that the headers on the main board line up with the sockets on the control board. Gently push them together until the sockets and headers are fully seated.

Flip the project over, and insert the final screws for the standoffs through the PCB, and tighten them down to the standoffs, as shown above. You can now install the knobs as well.

You should now have a completed MST VCO! Congratulations on the build!

If for some reason, you had troubles with your build, or it is not working right, you can check out the Troubleshooting Guide. It has loads of good information on some common pitfalls of building.

Next, check out our MST VCO Calibration Guide.