7805 causing noise on 12V supply line in this video?

[oldskool1]

I can't figure out what is causing this annoying whine on the 12 supply line when either the Arduino or keyboard encoder draw current from the 7805V regulator feeding off it. I am attaching a video because I think it might be easier to convey the problem by showing the system. The whine appears prominently in the audio outputs of the Virus synthesizer which is powered by the 12V line.

It sounds like the 7805 is a switching regulator in the audio band... I have never heard this kind of noise from a 7805 before. I really am lost with this and would appreciate some other eyeballs on it.

One other data point not mentioned in the video is that the Arduino and keyboard encoder both have 3.3V regulators on them.

 

[radardoug]

Its not going to be the 7805. You need to remove the other items one at a time and determine which one is causing it. Are they part of the synthesizer or addons?

 

[oldskool1]

Its not going to be the 7805. You need to remove the other items one at a time and determine which one is causing it. Are they part of the synthesizer or addons?

The Arduino and keyboard encoder are add-ons to the Nord and Virus synthesizers. The 12V line exhibits the same noise when either or both the Arduino or encoder are on, but not when the relays and leds are engaged, and they all draw from the same TL7805. How can those different boards make the same exact noise? This should be simple, but I can't figure it out.

 

[oldskool1]

You are right Doug, it's not the 7805.

I have a few more data points:

The whine emanates from the display of the Virus. It is not injected on the 12V line as I originally thought, it is actually on the GND line.

The whine is not present when the rig is plugged directly into a speaker. It is present when the rig is plugged into a mixer and then into a speaker. How this makes sense I'd love to know.

The whine (from the Virus display) is still only present when the keyboard encoder or Arduino are plugged in.

 

[oldskool1]

I found the problem! I had drilled a mounting hole in the 4 layer encoder PCB and the steel screw was shorting an internal layer to the the ground plane. This was hard to find, because the symptoms all pointed elsewhere. How this short caused the Virus display whine to appear, but only when going through a mixer, and not when directly plugged into a monitor is beyond me. I still don't understand the strange paths of the ground in this system.

But I do have to thank radardoug for "resetting" my head and causing me to look in other places than I was looking. Thanks Doug!

 

[radardoug]

No problem.