Modular Melody Maker Build Log 1: Acknowledge and Accept the Spaghetti 

As an ex pro-audio service engineer, I feel your pain. I strongly suspect one of your modules is putting noise onto the power ground, and that's what's causing the system to misbehave. You could try a semi-star ground, don't connect any grounds between modules, just run them all to a ground rail on one of your breadboards that is connected directly to the incoming ground. You could do the same with all the positive rail connections as well, that would mean you could twist the two supply wires together to prevent any inductive coupling. You could also try lifting the signal ground on the ADC input cable. Next up, I'd try decoupling and smoothing, add a 100n and 100uf cap across the power input to each module in turn, as close as you can. That might help prevent the troublesome module from creating the noise in the first place, I know some display driver chips are particularly bad at that. There's lots more I could suggest, but I hope that gets the problem solved. Though as others have said, perhaps it's just a dodgy connection somewhere, and a rewire is the first thing you should do.

Love the build log, looking forward to more! :) As a self-educated, creative-background electronics learner myself its reassuring to know that these kinds of 'stumped' moments really are universal. 😂 I'm still early in my own analog electronics learning journey but one thing I've seen a lot in repairing test gear is the use of a separate filtered power rail and ground plane for anything analog. Usually there's one or two types of small caps (electrolytic for filling in gaps, ceramic for filtering out high-frequency noise) between power and ground, some deliberate design to focus on 'star' grounding, and typically a separately regulated (usually with a linear regulator like a 7805) power rail just for ADCs/DACs or op-amps. Breadboards definitely make analog stuff more complex to play with though. My breadboard analog projects have all run into weird power rail blips, which I learned a bit more about from binge watching Ben Eater's lovely "breadboard computer" series. If I recall right in the earlier ones he gets into a bit of detail on where/how/why to drop power rail decoupling capacitors on breadboards to clean up power but I can't find the specific video at the moment. 😅 Hope some of that helps, and we'll all be looking forward to the next one! -fivesixzero

I just love watching these videos. Because I learn a lot and your voice is soo relaxing. 👧 Thanks a lot.

I love the yellow and green switches.

Excellent video 🏆 I’m learning more than i thought i would Thank you kindly

Не работал с подобными схемами, но было приятно погрузиться в процесс разработки. Удачи и вдохновения =)

I just found your channel today. You have a new sub for embracing the spaghetti. I have some spaghetti on my workbench right now!

Great buildlog video - like the format, especially when things go sideways. No build survives first contact with implementation! RE: the noise issue. I would strongly suspect a grounding or PSU-related issue, especially with power being derived from multiple places i.e the Eurorack PSU, USB power for the Pico, the 3v3 to 5v I2C stuff - all recipes for a ground loop or something similar. Not too familiar with the particular ADC and DAC you're using, but from past experience leaving any unused analogue inputs floating can be bad for noise rejection. Some ADC/DACs need to have separate analogue and digital grounds too - the datasheets will probably indicate if this is case. Good luck with the trouble-shooting. Sounds like you're on the right track.

With that large a tangle of spaghetti it is most likely to be a loose or swapped connection. I often find it easier to start over (much like patching a modular synth) when a build gets complicated.

Making videos as buildlogs is such a good idea! I wasn't exactly sure how I was going to document my own DIY synth making process but that's a perfect way of putting it! I hope you don't mind me stealing this idea.

This is so cool! I'm early on my journey but your videos are super inspiring!

Could current be limited or uncontrolled? Perhaps having some buffering from an op-amp between stages could help.

🙂 Modular Melody Maker. That's 3 Ms. You should trademark 3M - I'm sure nobody is using it 🙂

thats cool. but i really dont know any programming therefore i do not like arduino and such microcontrollers. and all that stuffs. i rather just use you know. IC chips , analog, ya know that sorta. thing. you ever play with CD4040 chip ? some interesting things.

I like you. #1 subs provider -> 'Promosm'.