Assembly procedure for 3 to 1 Precision Adder - V1.0c

Here is the recommended order to assemble the 3 to 1 Precision Adder module Version 1.0c. Please read the entire procedure before starting the soldering job. Feel free to adapt these steps to your needs and personal workflow.

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.

R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11 and R12 are 100 kilo Ohms, **0.1% precision** (Brown, Black, Black, Orange, Violet).

R19, R20, R25 and R26 are 1.5 kilo Ohms, 1% precision (Brown, Green, Black, Brown, Brown).

R13 and R14 are 100 Ohms, 1% precision (Brown, Black, Black, Black, Brown.

R15 and R16 are 27 kilo Ohms, 1% precision (Red, Violet, Black, Red, Brown.

R21 and R22 are 47 kilo Ohms, 1% precision (Yellow, Violet, Black, Red, Brown.

IC Sockets

U1, U2, U3 and U4 (TL071) require a 8-pin DIP socket. Be careful, the sockets are polarized. Align the notch to the silkscreen indication on the PCB. Do not insert the ICs themselves yet.

Small capacitors

Small, ceramic or plastic capacitors are not polarized.

C3, C4, C7, C8, C9, C10, C11 and C12 are 100 nano Farads.

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 1N5817 (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! An incorrectly positioned capacitor may explode.

C5 and C6 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.

Trimmer Potentiometers

Components mounted or aligned 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 on the PCB, without soldering them. Second, present the front panel over the components, then secure them in place by tightening the nuts. Example here: J1 and J8.

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 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.

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

Last steps

Test the module without U1-U4 inserted. Check voltage polarities at test points T5, 6 and 7.

Finally, insert the TL071 chips in their sockets. Be careful to not damage the pins. Please be careful: U1-U4 are polarized. Align the notch on the chip to the PCB indication.