millipz wrote:It seems to be a lively and helpful community you have here...
It is -- there are a lot of very knowledgeable and talented people here who enjoy helping others in a kind and supportive way. It makes this a very different and special forum from most of the others out there!
I will definitely read up on ground loops...
A 'ground-loop' is formed when two class-1 mains-powered devices are connected together via audio cables. What happens is that there is always some AC current flowing in the earth wires of the building's mains wiring. Any length of cable has some inherent resistance, and current flowing through a resistance creates a voltage difference across it. So when you plug one device into one mains socket, and another device into a different one, their mains safety earth connections are at slightly different voltages. If you then join those two devices with an audio cable, the shield of the cable effectively links their earths together and, as they are at different voltages an AC current flows in the audio cable's shield.
The ground-loop current flows from the building wiring, into one device via its mains cable, through the audio cable to the other device, and through that device's mains cable back into the building's wiring. hence the 'loop'.
Now, if the audio cable is a balanced one, the wanted audio signal is kept entirely separate from the cable ground -- it flows back and forth only over the hot and cold signal wires -- and there's no problem. (Well, actually there can be sometimes, but only if the equipment isn't designed and built properly!).
However, an unbalanced signal flows back and forth over the signal wire and the cable shield... but if there is a ground-loop current already flowing in the shield as well that inherently gets added to the wanted audio signal -- and that's when you hear those nasty hums and buzzes. And it doesn't take much ground loop current to make a nasty noise on an audio signal!
1. At what distance would the unbalanced connection begin to be an issue? This may be somewhat subjective and need testing. Is it a case of external interference or will the cables in the snake start to affect each other?
Crosstalk between cables isn't likely to be a problem even with 10 or 20 metres. What makes the difference is the destination (and source) impedance, the signal level, and the environment. The greatest risk is from external RF interference, so the nastier the environment, the higher the impedances involved, the lower signal levels, and the longer the cable all increase the risk of problems.
But if you keep the cables away from anything radiating nasties, work with normal line level signals and standard line interface impedances, you should be able to run out to 30 feet or more without problems. Shorter is always better, though!
2. Linked to the above, I am considering plugging the "wall warts" as you colourfully call them into a PDU, rack mounted with the XR18, and running power (barrel plug extensions) through the snake to the pedals. Maybe also a USB A extension cable for power to the OP-Z. might these power runs cause interference?
I'd hope not, but it depends on the quality of the power supplies! bear in mind that you may end up losing power voltage if you extend the supplies over long cables, potentially resulting in reduced headroom, lower output levels, and less reliability... So test carefully before committing!
