LZX Cadet-based Scan Processor

This scan processor is my headlong leap into DIY video electronics; it is comprised of several LZX Cadet video synthesizer modules. Vector patches are some of the more fun yet mentally stimulating patches to create, and I wanted to build a standalone system to free up other modules in my system. As a touchstone for the design, I referenced the simplified block diagram of the Rutt-Etra scan processor as described in Eigenwelt der Apparatewelt. My goals for this project were as follows:

  1. Identify and assemble LZX Cadet modules to fulfill sync generation, video input, luminance control, and ramp control function shown in basic Rutt-Etra block diagram.
  2. Create a public, living document to streamline component ordering for LZX Cadet modules.
  3. Design a laser-cut acrylic panel to hold each module.

Goal 1: Recreate basic Rutt-Etra functions with LZX Cadet modules

RE_block_diagram
Basic Rutt-Etra scan processor block diagram

I got inspiration for this project from discussions on the LZX Video Synth Community group, and subsequently reading the aforementioned section on Bill Etra and Steve Rutt in Eigenwelt der Apparatewelt. By building LZX Cadet modules, I sought to recreate the system illustrated by the block diagram above. As can be seen, the block diagram calls for a video input source, sync separator/generator, H/V ramp generator, 5 multipliers, and 3 summing blocks. Each of these operations could be realized with the following Cadet modules:

  • Cadet III – Video Input
  • Cadet I – Sync Generation
  • Cadet IV – Video Ramps
  • Cadet X Multiplier – Luma Contrast, H + V Size, Depth
  • Cadet VII Processor – Luma Brightness, H + V Position

When I embarked on this project in early December 2017, LZX had long-since discontinued the sale of premade kits. With the exception of a few B-stock kits, I needed to source components for each of the building blocks. LZX provides the Bill of Materials for each, citing Mouser part numbers for easy cart-building.

 

Goal 2: Create a public document to aid in sourcing Cadet components

While ordering the necessary materials for this build, I was inspired to help others quickly source components by compiling information into a Google Doc with pre-made Mouser projects. Per the recommendation of the LZX Facebook group, I made Mouser projects for each of the BOMs for easy order of duplicates. At the time of writing, there have been a few cases of parts going out of stock. Thankfully, alternative parts can be recommended, and the comments feature allows users to add notices in real-time.

 

Goal 3: Design a laser-cut acrylic panel

By this point, I decided I was far enough into the DIY hole that I may as well make a panel too. :^) Using the panels that shipped with the Cadet PCBs, I measured the hole diameter and position for each module, designed a singular panel in Adobe Illustrator, and sent it to Ponoko to laser-cut from 3mm clear acrylic. From this process, I developed a new respect for panel design — although it looks cool, the PCBs are tight, and patching quickly becomes messy. Furthermore, the 3mm acrylic proved too thick; I owe thanks to Chris Miller at the Bozeman Makerspace for using his CNC to counterbore 1mm out of each hole, allowing for the 3.5mm jack nuts to securely fasten!

Counterbored 3mm acrylic frontpanel, courtesy of Chris Miller
Counterbored 3mm acrylic front panel — thanks to Chris Miller @ Bozeman Makerspace!

Next steps

While I am able to perform the desired vector rescan functions, some debugging is necessary. The Contrast multiplier circuit introduces noise in the power bus, the Brightness processor circuit seems to be outputting a constant 1V, and the video ramps introduce some sort of logarithmic pattern in the raster (visible in the first demo). However, it’s still a very functional system!

I also plan to take advantage of the switch input on the 3.5mm jacks to create normalized connections for “semi-modular” functionality; note the engraved lines indicating typical signal flow. This would essentially create a default patch, allowing ease of use, and freeing up patch cables/panel space.

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