Audio in/out pins +/- confusion

#1

Hi Guys,

My board is sitting inside a 1U rack box.
It has 4 MONO jacks for in/out and a USB socket, so it is OK for me.
Now, I'm working on my studio, bought a few new furniture, etc., and I'd like to designs a new and proper front panel for the Axoloti.
I'm a bit confused now, I checked my connections. As I had some noise issues with the board, I think, I connected the jacks in the wrong way.
I used, for example, LOUT + and GND, and ROUT + and GND, same for the input.
Is it OK like this? If not, how to?

#2

Hello Snaper,
This is the first time I contribute in this community forum... glad is to help instead of asking for help, which I will need shortly :smile:

I'm quite new to Axoloti, but experienced in audio engineer stuff, lately I've been studying the Axoloti board to build an enclosure, and like you stumbled in some doubts regarding pinout wiring.

For what I can understand, the PCB pins marked with L IN+, L IN- and R IN+, R IN-, will allow a stereo "balanced" audio input in Axoloti. Using L OUT+- and R OUT+- will allow a stereo "balanced" audio output.

The two jacks that Axoloti has from "factory" are stereo in and out, but unbalanced, since each of the connectors uses one TRS JACK for L and R. I guess to save space and costs.

For the audio Jack soldering, you must use the following:
-TIP: Will use the pin marked with + (plus)
-RING: Will use the pin marked with - (minus)
-Sleeve: Goes to GND

I checked with a Multi-meter and found no connection between Jacks in the board, and the prototyping pins, that puzzles me. Not sure if they are isolated for some reason, or you can actually access more in/outs this way...

Hopefully somebody can shine some light here.

Well I hope this info it's of some help for you!
Cheers!

#3

I see, thank you very much.
I connected them in the wrong way then, used the + and the ground only.
I have some noise, mostly USB type noise on my outs, could this badly wired socket the cause?

#4

Hello Snaper,
Yes, in theory a balanced connection will eliminate some noise if it's introduced in the cable from axoloti to whatever amp or soundcard you connect it to. So this may help in a less noisy connection.

However, I'm not sure if this is your issue. Check audio jack for bad soldering point, but I think is due to powering the Axoloti with USB.

This is an important aspect because USB normally introduces noise in the audio stream when powered from a computer or similar source, check if powering the Axoloti using the DC Power Jack and avoid the USB connection helps in getting rid of the noise. USB may still be needed to transfer files to and from axoloti, but when not in use, better to just use the DC Jack.

Hope it helps!
Cheers.

PS: Hopefully Johannes or somebody with deep knowledge in the Axoloti board can shine some light in the description of Audio IO pins.

#5

Ok, so, little update.
Actually, (it is not the most beautiful way, I know), I soldered wires to the bottom of the board, and basically, "wired" out the original on-board connectors, to 6.3 mm jacks to the back of my 1U case.
I am very surprised, but my noise issue is now gone, I mean, totally!