I'm trying to build a guitar pedal switcher (efectively a box that provides multiple effect loops that can be independently bypassed from a single microprocessor) and while building a working breadboard prototype for a single loop, I've encountered some grounding issues which made me rethink my approach.

Now, I'm not exactly the EE, so grounding is a topic I don't grasp so well. Question is: do I need to route the audio ground as well, or should I just route the audio signal and link all grounds together?

  • \$\begingroup\$ Is the noise a 50Hz/60Hz hum, or rather digital noise ? Micro-controllers can be noisy depending what it is making. \$\endgroup\$ – CopperMaze Aug 30 '14 at 10:53
  • \$\begingroup\$ What are the "issues" you mentioned? \$\endgroup\$ – Andy aka Aug 30 '14 at 12:26
  • \$\begingroup\$ First, I noticed the sound was a little distorted and the whole thing started oscillating, without the signal going through the effects loop. I then realised audio ground from my guitar wasn't connected to power ground. Fixing that resolved the issue, but then I noticed the same problem on the loop part, so I connected the send effect audio ground to power ground. However, while bypassing the effects loop I noticed a distorted sound again, which would be fixed if I turned off the pedal (strange as it wasn't connected to the rest of the board - except for the ground connection). \$\endgroup\$ – CatalinM Aug 30 '14 at 12:39
  • \$\begingroup\$ Thinking I need to connect all audio grounds to power ground, I then realised there wasn't any point in routing the audio ground together with the signal, as it should be all connected to power ground anyway. I built another breadboard prototype without routing the ground and everything seems to be working OK, but I would be grateful if someone could confirm this is the correct way to do it. \$\endgroup\$ – CatalinM Aug 30 '14 at 12:41
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    \$\begingroup\$ I know too little about grounding to justify posting this as an answer, but you should connect all grounds to each other. There are some best practices you could use. First of all, use star grounding, joining every ground to a central point with a wire. As CopperMaze already said, microcontrollers and other fast switching stuff can be noisy, so it's a good idea to give all electronics a shared ground plane, and then connect that ground plane to the central star ground point with a wire. Also, physically separating digital and analog can greatly reduce noise. \$\endgroup\$ – Tom Oct 10 '14 at 11:59

It's been quite some time, so I'll go ahead and answer my own question in case any other nutjob with stupid questions comes through here:


I breadboarded the prototype and it all worked fantastic, without any hum whatsoever. Star grounding is a good idea to ensure you won't have any ground loops.

Also, I added an optocoupler into the design, to separate digital and analog sections. Will update answer after completing prototype.

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