Waveform Magazine Catwalk Cattenuator - DIY Build
As we tackled the Waveform Magazine Cattenuator, it was now time to tackle the new LPG/VCA. Like the previous build and the Mini Mult Catwalk, these modules take up about 12HP of space in your rack. Their footprint is small and their impact is huge. As previously stated, Waveform Magazine is on point with their Catwalk series. In case you have missed any of the previous builds or reviews, check out the quick links below to learn more.
Let’s get onto the builds shall we? Building the Catwalk VCA or the Catwalk LPG is relatively easy. The most difficult part of this build is assembling the vactrol or optocoupler as its sometimes called. An opto-isolator (also called an optocoupler, photocoupler, or optical isolator) is an electronic component that transfers electrical signals between two isolated circuits by using light.
You will be putting together 2 of the optocouplers for this set of Catwalks, so turn on your iron and get ready to dive right in.
Building the Optocoupler... (vactrol)
Use the supplied LED and the LDR to make the coupler. Start by taking each component and placing them end to end so that their legs are sticking out away from each other. Take the shrink tubing and place it over both components where they meet. Heat this tubing up to bring the two components together.
Seal it up as tight as you can so that light does not escape when triggered. You just build your first vactrol… good work! Now, make another and set it aside. There will be a total of two of these and that is a great place to start when laying out the build.
Next, separate everything out and remember that the LPG uses the supplied capacitor whereas the VCA uses the 1K resistor. The top panels are the same on both sides so do not be confused about that. One side is for the LPG and the other is for the VCA.
Catwalk LPG - Time Lapse Build (v1 - slower)
Catwalk LPG - Time Lapse Build (v2 - stylized)
Resistor or Capacitor?
Starting with the VCA, take the 1K resistor and solder into the points next to the output jack. You will do the same with the capacitor on the LPG. Once these are in place on each board, grab the jacks (there are 3 per board) and begin placing them in the correct locations.
Now flip the PCB over and tack down the middle leg of the jack so that it stays in place as you continue to move forward with the build. Do not tack down the other legs just yet.
Catwalk VCA - Time Lapse Build (v1 - slower)
Catwalk VCA - Time Lapse Build (v2 - stylized)
The Build ... continued
Grab the vactrol you placed aside and start by placing the short leg of the LED side into the square pad on the PCB. Once you set the LED, carefully bend over the vactrol and place the LDR legs into the pads that are located on the sides of the output. Tack down the LED legs of the vactrol and set it aside. Here is where it can get tricky… we have to take the other LED that came with the kit and go “around” the vactrol into the PCB.We took some closeup shots and actually redid our LPG after this build to clean up the module. Our VCA we nailed on the first shot. Anyways, bend the legs of the LED so that the vactrol can be in-between the legs of the LED. You might have to use fine tipped tweezers to make the bends and get the legs placed correctly. As with anything, make sure the legs of the new LED are not touching the metal legs of the vactrol.
Just take your time and slowly bend them around the vactrol. Do not solder the LED legs just yet.
Catwalk LPG/VCA Gallery
Lining it all up...
Finally, we get to the panel placement. This is where it all comes together. If you are building the VCA, make sure you are using the correct panel side and vice versa for the LPG. Place the panel on top of the jacks and LED that you recently placed. As long as everything lines up, hand tighten the nuts onto the jacks to hold the panel in place.
Flip the board over and tack down the rest of the jacks and the LED once it has been pushed up through the bottom of the panel. When everything is in place and soldered down, pat yourself on the back you have completed the Waveform Magazine Catwalk LPG/VCA. Now it is time to mount them to your rack.
Mounting the Catwalk
Scope out a place that measures approximately 12HP from hole to hole. You might need to rearrange your modules to create this space. Don’t forget that you can install on the top or bottom of your modules too. When you have found your spot, remove the screws that held the modules you will be using to mount the Catwalks to.
Insert the hex standoffs into these holes and hand tighten them into place. Make sure you do not over-tighten. Place the Catwalk over the hex standoffs and attach it to the standoffs with the screws that were provided. You might need to use a washer with the standoff, so if you do make sure you place it between the panel and the standoff and not above the panel.
If things seem loose once everything is in place, you can use a small set of needle nose pliers to carefully tighten down the standoffs. You are now ready to patch and play!
Catwalk LPG/VCA Final Thoughts...
Waveform Magazine has done it yet again with its Catwalk series. This project is innovative, inspiring and thoughtful of them as rack space is very cherished by artists. As we wind up our review and build guide, we have to say thanks to the gang at WF. We can’t wait to see what the next project is!
If you have questions about the build process or suggestions/feedback about this article, feel free to let us know by contacting us We look forward to hearing from you!
Until the next build …