Try adding ferrite torus to the data cables of your midi modules.

https://www.amazon.com/MAG-FT-140-43-Ferrite- … 39&gad_source=1

Run a figure 8 through the torus.

Oh, shit, you already tried that?

Have you tried putting the rings on the POWER cables, or on the VGA cable?

Hi, I also think that ferrites are a good idea.

If it doesn't help, some ideas:
a) try turning the AC plugs, maybe "hot ground" is an issue

b) try to use galvanic insulation.
A pair of opto-couplers or a pair of AF transformers can help to electrically insulate audio connections.
In its simplest form, a pair of capacitors can be installed in the audio line (for audio, a few µF are enough).
Maybe there are commercial solutions.

c) this isn't for beginners, but there are separation transformers for AC devices.
Just remember that things like fuses and RCDs don't work anymore if something goes wrong on the other side of the transformer.

Anyway, these are just some ideas that come to mind.

Thanks for trying to help me. I have already put several feritte rings on and I will receive another 20 just now. No matter how much I put it everywhere (VGA cable, midi, audio), I don't see any effects! I'm going to add more but I doubt :s

I also put the power supplies of my midi modules on other sockets, no change.

I have learned a little about octocouplers, but I admit that we are entering an area that I am completely unfamiliar with 🙁

Is the outlet ground properly earthed?

wierd_w wrote on 2024-05-29, 14:46:

Is the outlet ground properly earthed?

Yes.

Have you checked if the data cable's ground/shield is properly connected to the earth ground?

Sometimes vintage computing devices dont properly connect the ground, leading to 'floating' grounds, and unreliable ground states.

(The tape cable on old TI99/4A systems have this problem, and expect the tape deck to connect/combine grounds. This leads to ground-hum, and failure to decode fsk data from the tape. I've had to cobble together kludges to make this work properly from this incorrect ground loop design.)

I'd use, briefly and temporarily of course just for the test, an adapter that lifts the ground (that converts for example 3 pins->2) on the power supplies one by one in order to maybe identify a specific device.

Thanks a lot for your help.

I think I have identified the two (and yes) guilty.

I currently power my Yamaha mod and my Roland CM64 with 2 universal adapters (https://www.amazon.com.be/dp/B08R6VSK3F?psc=1 … customerReviews)

I have the impression that they are the problem... I don't know how to solve the problem.