CCTV Active Multiple Build Guide
The Active Multiple Kit is an easy-to-build, low parts count eurorack module that lets you create perfect copies of voltages or audio signals.
An Active, or "buffered", multiple is especially useful for splitting signals going into low impedance inputs, especially common on vintage equipment or clones of vintage modules. An Active Multiple amplifies each output at 1:1 gain, providing current gain and isolation between outputs. If you find that using a passive multiple causes signal distortion or pitch changes, an Active Multiple might be what you need.
The kit contains everything you need to build an Active Multiple. The BOM (Bill of Materials) below is a spreadsheet outlining all components included in the kit.
We'll start with the resistors and diodes. Resistors can go in either way around, but pay attention to the polarity of the diodes. The stripe on the diode needs to match the stripe on the PCB footprint.
Solder the legs.
And clip them off!
Next up we'll solder the 2 TL074 Op-Amps. These are 14 pin integrated circuits, and each chip contains 4 Op-Amps. Op-Amps can be configured as 1:1 gain buffers, perfect for our multiple application.
It's very important that you orient the chip in the correct way! The photo below shows how the notch on the chip matches the notch on the footprint.
Both op-amps are oriented the same way. Bend their legs a little on a table to get them in line and make sure they sit flush against the PCB.
Now is a perfect time to DOUBLE CHECK YOUR ORIENTATION!!! Once they're soldered it will be very difficult to fix. Solder each pin on the underside. These pins do not need to be cut.
Now we will move on to the 4 100nF ceramic capacitors. These do not have polarity (they can go in either way). These capacitors are used for power supply filtering. Solder these the same way you soldered the resistors, and clip off the excess legs.
Insert the 8 jacks as shown on the footprint. Some jacks share one ground point, so their legs need to touch, as shown in this photo:
Last component is the power header. Insert the short legs of this connector through the BACK SIDE of the PCB. This is the only component that goes on the back.
All that's left is the panel! Thread the nuts on the jacks and tighten them down.
Test your module by sending a signal into the IN jacks and patching out through the OUT jacks. You should see the exact same signal.