Lots of noise on 16 circuits in one rack unit

[Esppse]

Hello,

A while back, I started a rack project with 16 circuits in it. They all have in and out Jacks on the back, 16 ins, 16 outs. The Jacks are isolated from the chassis, and so is the ground from the power coming in.

There are 6 isolated DC plugs entering the unit, so each about 3-4 circuits share the same power. When I rested the unit, there was little to no noise, I tried one effect at a time, and one power supply at a time.

I am getting a bit of noise and I'm trying to isolate it.

Should I ground the chassis to all the grounds? Everything is isolated from it now, which means I'm considering grounding everything together, which defeats the point of isolated DC outputs?

As far as the DC plugs, they are 2 conductor, like 2 separate wires joined, instead of the one wire wrapped in a shield. They all travel together about 3 feet from the rear power supply mounted in my rack, to the unit. Could this be the source of the noise?

https://www.amazon.com/Gauge-Speaker-Audiopipe-Black-Copper/dp/B01BYJ4EF2

[DIY Bass]

Standard practise would be to ground the casing.  I suspect you will get less noise as a result.

[blackieNYC]

Show us this thing!

[ElectricDruid]

I think in this case the separate power supplies might actually cause you more trouble rather than less.

The reason why is because the "grounds" will not actually all be at the same voltage. There'll be differences from one to another, and the longer cables back to the power supply will make that worse by increasing the resistance of those return paths to ground.

I'd have been inclined to provide one hefty power supply for the whole rack, with the rack and all the panels grounded for shielding, and then make sure each circuit has a low resistance path to a single star ground point at the back of the rack somewhere. Like that, ground should be ground, everywhere. Of course, it's easy for me to say this, but it doesn't prove that doing it my way would ultimately finish up any less noisy than yours...

[amptramp]

If this is a design using mainly op amps, I would provide a regulated ±12 VDC supply so supply currents do not get mixed up with ground currents.  Since you have control of the input impedances of each effect, you can make the input impedance high so the output impedance doesn't have to be as extremely low as it would be for a general-purpose pedal that is expected to connect to everything.

As for hum, I agree that a star ground with the chassis also being grounded to it is the best way to keep the grounds equalized.

[Esppse]

OK thanks for the suggestions all. I found out that the Analog bit crusher circuit was leaking noise into everything else for some reason. There is still a bit of noise, I'll try out the mentioned ideas!