[SOLVED] Digital noise coming from axo

#1

Hi,

I stacked 4 axos on top of each other and connected their power pins (big fat 1mm copper wires). I power the axobank from a decent 1500mAh, 12V power supply.
I also bridged the MIDI-in pins, so If I connect one DIN midi-in, all axo's are connected.

image.jpg1131x848 291 KB

image.jpg636x848 157 KB

This all works great, but I have a digital hum
video link
So I started measuring, and I found something weird:

if I put my multimeter in the "beep" mode, WHILE AXOS POWERED ON

BLACK probe on the case, RED on axo GND multimeter is beeping
you can see in the video that when I'm pulling the axo to make contact with the case... it beeps.
RED probe on the case, BLACK probe on Axo GND (any) multimeter silent

WHILE AXOS POWERED OFF
always connectivity (beeping)

the sound you hear goes away when making contact between Axo and case. You see me pushing the power plug in de video, I thought it was the plug, but it happens anywahere I push the axo.
Should I just solder the case to the axo GND?
is this a good idea?

#2

I made a scope picture of the noise, it's the major sinelike wave, not the noise... that reamains, although on a flat like when I make contact.

image.jpg1131x848 297 KB

also, I found out the hum is exactly 3000Hz...

image.jpg382x848 94.8 KB

hope this helps

#3

Wow what an axo tower :grinning:

I have had the same kind of noise when putting several axos to the same power supply.

Did you connect the ground to the case?

If that doesn't help I can recomend getting one of these:
https://www.thomann.de/de/harley_benton_powerplant_iso_1_pro.htm

That isolates the grounds between the axo boards. I have had the same 3k noise + lots of noise from the leds of my midi controller. These isolated power supplies really solved it for me.

I don't think this is a good Idea. You are basically doing an unbuffered midi split/thru. As far as I know you could loose midi bytes like this, and thus have glitches in your signal. So I guess an active midi splitter or going making a midi chain between the boards would be better.

#4

It's an old hard drive enclosure

I don't think that would help, because sometimes (well basically always) I plug audio from one to the other axo, thus connecting the grounds anyway. I noticed hum is different with less/more LEDs lit on the midi controller, but also with a different USB cable...

But so I connected the boards to the case...
like this, using a broken 230VAC wall plug

image.jpg636x848 222 KB

problem solved for now... I can always look for the isolated power supply option, did not know about it yet...
I never experienced problems with the MIDI yet. If it occurs I know where to look, but for now, no problems!

Thanks!

#5

I also had audio going between my boards. Axoloti has a ground loop break circuit at the audio in, so I can tell you it does work, and for me also solves the problem with the LED on the midi controller.

Glad that grounding to the enclosure seems to work though!

#6

Is the supply a switching supply? Often they will introduce noise into audio systems (ty[ically high frequency though).

#7

I've tried both, I think (a small one from a soundcard - switching, a big bulky heat generating one, probably not switching...)

both had the issue, but it's gone now!

#8

I finally bought one of these... found out the polarity is reversed, the connector is center-negative, How do you connect these?

#10

I cut the cables and crossed them, which seemed to be the easiest option... 10 minutes of soldering for 5 cables.
The digital noise is gone, replaced by a softer lower frequency analogue noise hum, but only on very high gain....