for quite I while now I'm working on a setup that has 1 external Input that is being sent to two boards and audio that is being sent back and forth between the two boards via the rts pinouts on the back of the board.
I tried to make a drawing of it, I'm sorry I'm really bad at documenting this technical stuff:
Just once more in text here:
External Input, goes into Board 1, Jack In and is being tapped to Board 2 to Pin T (left input)
Connection from R Out to R In between both boards, back and forth (right output / input)
Each Board sends out via T (Left) in Mono and the outputs are summed in a little mixer, this one:
The Boards and a little Mixer run of the Same 12V DC power supply.
Furthermore I only send Midi from Board 1 to 2, and got GPio connections between the boards.
The Problem is:
I've got a lot of noise with this configuration. It is not that 50hz grounding noise But more like white noise and a really high pitched drone.
I tried powering all from a battery but I've got same noise still.
When I skip the little mixer and go directly into the main Sudio Mixer the Noise gets even worse. So it seems as if the little china mixer cleans the signal up, but the whole setup is still quite noisy.
Furthermore the leds of my midi controllers (Nanokontrol 2, Launchcontrol XL) add some more high pitched drones.
Any suggestions how I could get rid of the noise?
Is the Groundconnection between the boards important? Right now I went from the Input "S" (sleeve of the jack) to a GND of the other board, but they also share a ground via the powersupply.
I also tried powering the little mixer with seperta PSU, no effect.
This is what Ableton's EQ analyzer shows me (I bosted the noise a lot)
With a really loud peak at 3k, low frequency rumbe and two hearable tones at 150 and 200 hz (harmonics of 50hz?)