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Simple Gates Build Guide

Updated: Oct 22, 2021

Simple Gates is a dual low pass vactrol gate module with 3 filter types and a 2-pole mode in a 4HP DIY Kit. Inspired by classic Buchla designs, Simple Gates is entirely passive, drawing power from the incoming CV only.

This Build Guide will outling the construction of this dual gate from the kit.

Schematic and Board View files are available at the bottom of this page.

The BOM (Bill of Materials) outlines all the parts included in this kit:

Firstly, solder the 1K resistors. There are 6 of them. Orientation does not matter, but you'll receive Synth DIY cred if all the colour stripes are in the same direction. Solder each leg on the other side and clip them down with side cutters after.

Next solder the 100nF Film Capacitors, there are 2 of them. The 100nF are the smaller red boxes, do not get them confused with the larger 1uF capacitors, or your switch will work in the opposite direction.

1uF Film Capacitors go right next to the 100nF ones.

Prepare the vactrols by bending the legs at 90 degrees to the body using needle nose pliers. When bending the ST VTL text should be facing upwards (while bending the legs downward). Be gentle with this step.

Note: If your vactrols do not say ST VTL, you have Luna brand vactrols in your kit. Skip down for instructions on how to install the Luna Vactrols.

Position the vactrols as shown in the photo. The ST VTL text should be inline with the 'VACTROL' text on the board. Make sure all 4 pins are through the PCB and solder them on the other side.

Luna Vactrols

We are in the midst of a global component shortage, and us humble kit builders are doing the best we can. Some kits will be supplied with Luna Vactrols instead of the ST VTL type. These have almost identical electrical properties, but are physically a little different. Luna Vactrols are small cylinders with text written around them. They look like this:

The long legs are the LDR side, the shorter legs are the LED side. There is a small dot to indicate the cathod (negative, -) side of the led.

You'll need to bend the legs to match the footprint on the PCB. If you're looking at the dot, the legs need to be bent down.

The Luna vactrol takes up less space than the ST vactrols, bend the legs so it sits centered on the footprint. In the following photo the small silver dot is at the top right.

At this point we can fit the 1/8" jacks. Be sure to solder one leg first and check orientation, flatness and striaghtness before committing and soldering the other 2.

The LEDs and switches will be soldered with the panel in place. Double check the orientation of your LEDs when inserting - the longer leg is the ANODE and the shorter leg is the CATHODE. The ANODE is inserted in the top most pad. Compare yours to this photo before soldering.

Add some nuts to the switches (Note: The 2 switches use a different type of nut than the jacks do) and fit the panel with 2 jack nuts to keep it in place. You can now adjust the switches and LEDs so they are positioned perfectly, then solder them in place.

Simple Gates has an optional '2 Pole Normalization' solder jumper on the back. What this means is the output of the first gate can be fed back into the input of the second gate. This results in a sharper cutoff at the second output than the first. This normalization can be broken by inserting a jack on the input of the second gate, or the output on the first gate.

CV Input 1 is normalized to CV Input 2. To break this, insert a cable into CV input 2.

If you'd like to make use of 2-pole normalization (recommended) - Close the jumper with a lump of solder.

You are ready to test!


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