This could also be a bad jack in combination with grounding issues. To help troubleshoot, when the humming starts, try touching a wire to the lip of the jack at each end of the cable at the same time and see if the humming goes away. Also, does additional wiggling of the cable ever stop the humming?
So far I think this is the one that I have done that I am most pleased with.
Eurorack modules are capable of much higher output levels than line level gear. You can send eurorack signals directly into line level gear if you are very careful, but a mistake could damage the line level gear. It's a lot safer to have an interface module. Also, although line levels going into eurorack gear can't damage anything, the level does need to be boosted or it will be very quiet. I have the Audio Interface II and am quite happy with it.
Do all the modules work if connected by themselves? Also, a lot of power supplies have overcurrent protection and will shut themselves down to protect your equipment if too much amperage is drawn. It's possible you could have a power supply that doesn't match it's published ratings or a module drawing more power than the spec. Have you tried starting with just one module and adding the others back one at a time?
Even though it's not DIY or pure analog, you might want to check this module out anyway. I just got one and it seems a perfect fit for the styles you mentioned.
https://www.modulargrid.net/e/4ms-company-spectral-multiband-resonant-filter
Below is the layout for my first eurorack modular synth. The actual case is an SKB 3U shallow rack with a Happy Ending kit. It's a bit of an odd duck because I already have the Korg MS-20 mini, Korg SQ-1, Arturia BeatStep Pro, Arturia KeyStep, etc. I looked toward adding sounds rather than duplicating functions that I already have for my first purchase. In spite of that, I think it's a fairly interesting synth even standalone. I've already gotten some intriguing sounds out of it. The guys at Control Voltage in Portland did a great job helping me out.
So now that I've explained a bit about my synth, what would you suggest for the wish list that I'll be working off of when I'm ready to add another row?
