Ground hum

alfred · 2014-12-09T02:06:37.000Z

I experienced some nasty AC hum out of the stereo outs of my A4 (no USB connected). Strangely it was only present when I connected the A4s MIDI out to sync my pedals. The only way to prevent the hum was to put two (very expensive) line isolator boxes in between the stereo outs of the A4 and my practise space mixing desk.

I recently changed my setup and now I am running the A4 sync into an MPC1000 and use the MPCs MIDI output to sync my pedals. The hum is not present anymore in this new setup but I thought I put the info out there in case someone at Elektron wants to look into this.

Could it be there’s something wrong with the grounding of the A4s MIDI outs? Has anyone else experienced problems like this?

hellcore · 2014-12-09T03:53:54.000Z

""alfred"":

I experienced some nasty AC hum out of the stereo outs of my A4 (no USB connected). Strangely it was only present when I connected the A4s MIDI out to sync my pedals. The only way to prevent the hum was to put two (very expensive) line isolator boxes in between the stereo outs of the A4 and my practise space mixing desk.

I recently changed my setup and now I am running the A4 sync into an MPC1000 and use the MPCs MIDI output to sync my pedals. The hum is not present anymore in this new setup but I thought I put the info out there in case someone at Elektron wants to look into this.

Could it be there’s something wrong with the grounding of the A4s MIDI outs? Has anyone else experienced problems like this?

DIN MIDI is opto-isolated by design. Sounds like you have a ground loop between devices which is pretty common. Did you rearrange your power connections/strips when you MIDI synced the pedals?

Make sure your earthed devices share the same power strip.
Optionally, try non-earthed devices on their own strip (like the A4 and, I’m guessing, your pedals).

Try the setup with your monitors powered off and using the headphone out on your mixer to see if the loop is between your mixer and monitors or your sounds sources and mixer.
Are you using balanced cables and/or getting a good connection? Check for dirty jacks /sockets/broken cables etc…

alfred · 2014-12-09T04:57:40.000Z

yes, as i said the ground loop can be broken by putting line isolators in between A4 and mixer.

but that doesn’t change the fact that it is definitely MIDI connection related. as i said:
MIDI connection in -> hum
MIDI cable out-> no hum
no other changes made

i even tried it with a MIDI splitter box in between which is definitely opto-isolated. but it was the same. maybe there’s something weird with the A4 MIDI output.

t · 2014-12-09T08:20:40.000Z

MIDI is sometimes grounded to the case which can also result in ground loops.

hellcore · 2014-12-09T23:09:29.000Z

""alfred"":

yes, as i said the ground loop can be broken by putting line isolators in between A4 and mixer.

but that doesn’t change the fact that it is definitely MIDI connection related. as i said:
MIDI connection in → hum
MIDI cable out-> no hum
no other changes made

i even tried it with a MIDI splitter box in between which is definitely opto-isolated. but it was the same. maybe there’s something weird with the A4 MIDI output.

Is the pedal connected by midi both in and out? Try using only MIDI out from the A4.

MIDI inputs should never (as in, by design) be grounded, only outputs. If you have a multimeter you could test this yourself to check for a defect.

Edit: Reading again about the splitter… sounds like the MIDI in on the pedal is grounded… Try with the A4 not MIDI connected, just audio and the MIDI from the splitter to the pedal?