I built a custom Hz Interval Scaler module. I'm not used to V/Hz systems and didn't think scaling was easy but it is with multiplication, unlike addition in V/Hz modules. The math isn't perfectly accurate but within 0.1% as shown in this document.
V/Hz Scaling Calculations
I made the panel using 1.5mm anodized aluminum with the print graphics feature from FrontPanelExpress. There is a single CV input which is scaled to 6 different intervals: -1 octave, no scaling, minor 3rd, major 3rd, major 5th +1 octave. There are four separate channels, each with two paralleled outputs.
The PCB is hand wired and uses +18 and -9V. The +18V supply is required to reach an 8 volt CV output. Each scaler has a gain trimmer and offset trimmer. To minimize dependence on the power supplies, a +/-5V reference supply is generated for the trimmers.
I was able choose a layout that minimized hand wiring of sections. Yellow is the power supply wiring and blue is the signal wiring.
The Hz Interval Scaler works great. This video shows it in operation controlling four 4720A VCOs.