Assembly procedure for Simple VCA 1.0

Here is the recommended order to assemble the Simple VCA module. Please read the entire procedure before starting the soldering job. Feel free to adapt these steps to your needs.

This is the front side of the board we are populating.

This is the back side of the board we are populating.

Resistors

Start by soldering the smaller components. Resistors are not polarized.

R2, R3, R4, R5, R11, and R13 are 100 kilo Ohms (Brown, Black, Yellow, Gold).

R6, R7, R8 and R10 are 470 Ohms (Yellow, Violet, Brown, Gold).

R9 is 33 kilo Ohms (Orange, Orange, Orange, Gold).

R12 is 10 kilo Ohms (Brown, Black, Orange, Gold).

R14 is 1 mega Ohms (Brown, Black, Green, Gold).

R15 is 1 kilo Ohms (Brown, Black, Red, Gold).

IC Socket

U1 (LM13700) requires a 16-pin DIP socket. Be careful, the socket is polarized. Align the notch to the silkscreen indication on the PCB. Do not insert the IC yet.

Small capacitors

Small, ceramic capacitors are not polarized.

Eurorack power interface

K1 is the 10-pin power connector. This connector is polarized. Align the notch to the silkscreen indication on the PCB.

D1 and D2 are 1N5819 (or equivalent) diodes. They are mounted *vertically* with the Cathode facing up. The Cathode side is identified by a white (or dark) band on the diode body. The Cathode pad is identified on the PCB by a white band and by the square shaped pad. Please, see pictures for more details.

Bigger capacitors

Electrolytic capacitors are polarized. Be careful! Incorrectly positioned capacitor can explode.

C4 and C5 are 10 micro Farads, 25 Volts minimum. Align the negative side, indicated by a white band on the side of the capacitor body to the white silkscreen indication on the PCB. Also, the positive side of the capacitors is the longer leg (opposite to the white band), and is to be placed in the square shaped pad. Please see pictures for more details.

Components mounted to the front panel

I highly recommend to not solder immediately the components that are attached to (or to be aligned with) the front panel:

Instead, I suggest to first position the jack sockets and the potentiometer on the PCB, without soldering them. Second, present the front panel over the components, then secure them in place by tightening the nuts of a couple of jack sockets (preferably the two furthest apart) and the potentiometer. Example here: J1 and J5 and the potentiometer R1. If you can, tighten all the nuts.

Once everything is in place, solder only one pin per component. Check the alignement. Reflow the soldered pad for any component that would require an adjustment.

When you're satisfied, finish by soldering all the remaining pads.

This manipulation can be tedious, but the goal is to get both a perfect alignment of the controls and avoid any tension on the solder joints. If you start by soldering the pins before, and tighten the nuts and screws afterward, you might risk to damage the pads on the PCB, bend the front panel and get poorly aligned components. Of course, the difficulty here is to keep everything in place without soldering. If needed, you can solder just one pin before positioning the front panel, but remember to reflow that pin once the nuts are tightened, in order to release the tension on the pad.

R1 is 9mm "Alpha" style linear potentiometer. If it comes with a protruding tab on its front (below the shaft) remove it with pliers before assembling it.

Place the front panel, secure it with a couple nuts and the spacer. Then solder one pin of each component, as discussed above.

Last steps

Test the module without U1 inserted. Check voltage polarities at test points T1, 2 and 3.

Finally, insert the LM13700 chip in its socket. Be careful to not damage the pins. Please be careful: U1 is polarized. Align the notch on the chip to the PCB indication.