Noisy outputs on preenfm2 with cables but not with wireless system

[Brockstar]

So I've been rearranging my stuff and noticed if I use 1/4th guitar cables in the preenfm2, there's a bad hum for some reason, but if i use my line 6 wireless unit, it works fine with no hum. It's not my cable or system as I'm now using the cables fine for something else. What is causing this hum and how can something like this be fixed? I'm a bit pissed because the person I bought it from a few months ago may have known this too.

[vurt]

could be a lot of reasons for hum when it comes to machines. grounding being the most common. your mixer (or whatever you connect to) and the preenfm2 should share a common ground.

if there's no hum with the wireless thingy (no idea what it is) then it should tell you its clearly not the preenfm2 which is the problem..

[served]

You should describe more on how and where you are connecting this.
Also what Psu are you using to power it?
There is no reason why preen should produce humm noises. Other than psu or grounding issues.

[vurt]

Powering with USB can absolutely cause ground hum.. The beatstep pro is for example a device which is known to cause this, there's even an USB adapter (ground loop adapter for it to get rid of the problem.

[vurt]

the ground hum obviously does not carry over plain air, it needs the cables to carry over... try another power outlet, preferably connect the preenfm2 to the same power line that you have your mixer/soundcard connected to.. but try various ones. i have terrible hum from my speakers, all depending on which power outlet i use.

[vurt]

the power outlet in this case is the USB connection on your computer.. just buy one of those 5v adapters for usb's and put it your usb cable into that and try the usb adapter in various power outlets. if you have a mobile phone you probably already have one of those adapters.

[Xavier]

The best signal/ratio i had was with wall adapter (9v or 7.5v), 500ma is enough, ground outside.
To use the midi over USB unplug JMP2 jumper.
Midi over USB will continue to work without providing the 5v.

Computer USB and even many USB wall adapter are often very noisy for the preenfm2.

[Paulus]

If you refer to this: https://www.thomann.de/fr/visual_sound_1_spot_9vdc.htm
It will not work, the positive is on the outside barrel and the negative on the inside. You need the other way around:
+ Inside and - outside (This should be printed on the PSU: https://upload.wikimedia.org/wikipedia/commons/thumb/2/2e/Polarity_marking_center_positive.svg/800px-Polarity_marking_center_positive.svg.png)

9V is fine.