Building a Eurorack 3340 VCO – Part 3 Finishing the VCO Breadboards

This is part three of the Eurorack 3340 VCO build guide. In part one, we covered the 3340 VCO circuit schematic and bill of materials. In part two, we built the three boards comprising the Eurorack module.

With the three boards built, we now add the pin headers to each board, using the other boards to help with alignment. The photo to the right shows the final pin header configuration, and the following steps detail the order in which we recommend adding the pin headers to the boards.

On this page

Photo of the Eurorack 3340 VCO from the side showing pin header alignment

Adding pin headers to 3340 VCO Core Board

We’ll use the VCO I/O board to help us align the VCO core board’s six 1×10 female pin headers and four 1×2 female headers, PH1 – PH10.

1. Insert six 1×10 male pin headers in their female equivalents and four 1×2 male pin headers into the female equivalents. We are using the short female pin headers, not the longer stackable type. 

2. Position the combined headers on the VCO core board. The female headers should be on the VCO core board, with the male headers pointing upward. Position the VCO I/O board on the male end of the combined headers. Flip both boards over, ready to solder the female pin headers to the VCO core board. 

3. Check that the IO board has the same orientation as the VCO core – the screen-printed numbers should correspond with the number one at the top.

4. Solder one pin of each of the ten combined headers to the VCO core board. Check they are perpendicular to the board before soldering the remaining pins. The addition of the IO board helps align the headers correctly.

5. Solder the male side of four 1×2 headers to the VCO IO board; these carry power between the boards. Do not solder the six 1×10 male headers to the IO board. They will mounted on the Control Deck in the next step.

6. Gently remove the IO board with its four 1×2 male pin headers from the VCO core board. For now, leave the six 1×10 male headers in their female equivalents on the VCO core board.

Adding pin headers to 3340 VCO Control Deck

1. Position the Control deck on the male end of the combined headers you solder to the VCO core board in the last step.

2 Check that the Control Deck has the correct orientation – the four output jacks sit over the power connector of the VCO core board.

3. Solder one pin of each 1×10 pin header to the Control Deck. Check the pin headers are perpendicular to the Control Deck before soldering the remaining pins. 

Adding the power connector

1. Separate the VCO core board from the Control Deck.

2. Solder the power headed J10 to the rear of the VCO core board. If using a box-type power connector, ensure that it is correctly oriented so the red stripe on the power cable aligns with the white screen printed bar on the -12V side of the power connector – see photo.

Adding stackable pin headers to the VCO IO board

We’ll use the Control Deck to correctly align the six 1×10 stackable female pin headers for soldering to the VCO IO board.

1.  Push six 1×10 stackable female pin headers onto the six male pin headers you previously soldered to the Control Deck.

2. Turn the Control Deck over and slide the VCO IO board on the long pins of the stackable headers.

3. Check the IO board’s orientation. Row number one should be at the top above the Control Decks two CV input jacks, J1 and J2

4. Solder one pin of each stackable pin header to the rear of the VCO IO board. Check the alignment before soldering the remaining pins.

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