I’m using the second phones output of my Xone 96 to sample live on my Octatrack mkii. It means I can select the source to sample independant of my mix. However, using a normal stereo TRS to L&R mono TS splitter caused a very bad ground loop hum.
This sometimes happens when trying to send an unbalanced stereo output (e.g. headphone out) to balanced mono inputs like on the Octatrack mkii.
I resolved this by making a stereo TRS to L&R mono TRS splitter where the ground goes to both rings on the mono ends, not the sleeves.
You could try a cheap pair of isolating transformers like this:
They’r change the sound a bit but whether its for the better or for the worse is subjective. I’ve got a pair of old DuKane isolation transformers (the kind that would have been in a cheap mixer in the 60s) that I run stuff through a lot because I like what it does to the sound, but I have no idea what something like what I linked would do to it.
Since you’r eOK with soldering, if you wanted some nice sounding, professional transformer balancing and could spend a bit of money, a pair of Jensen 1:1 balancing transformers is pretty affordable as good transformers go:
Just wire up TRS and TS jacks to the balanced and unbalanced sides and put it all in a box and you’re set. Balancing AND isolation AND a little subtle but nice coloration.
Unfortunately, anything approaching transparent in the world of transformers doesn’t come cheap (base line would be around $100 minimum per channel) but that doesn’t mean the cheaper ones can’t ahve their own useful flavor.
Anyway, it sounds like your splitter cable is wired your Octatrack’s inputs don’t have the ground connected at all, you’ve got the ground from your stereo out connected to half of the balanced audio input in the OT, so the first thing to do would be to sort that out. The shielding on your cables would normally be collecting any electromagnetic interference and routing it to ground, but you’ve got it routed to your inputs instead (on top of any ground loop issues you might have and also on top of the cables no longer being properly shielded, and on top of the two pieces of gear no longer sharing a common ground).
The shield is going to the ring and the sleeve is left floating, by design I guess.
Using a TS at the Octatrack end connects the ring to sleeve, and as the sleeve is connected right to left at both ends it causes a ground loop.
Having the ring floating and just connecting the shield to sleeves leaves you with the same problem.
Pulling the rings to ground is a fine solution in my mind, as the rings aren’t connected L-R so no loop occurs and the cable is still shielded.
Transformer isolation is wonderful but probably overkill in this situation. It would be 100% necessary if I was having ground issues between two balanced devices. But I might yet make a transformer box as I do love the subtle warm sound of jensens and cinemags!
Right, but because the Octatrack’s inputs are balanced that means the shield is connected to the audio input rather than ground. So you have no shielding, and the EMF that the shield picks up is part of your audio signal.
If you put a TS cable into the inputs, the ring is shorted to the sleeve and both pass to ground. Because you left the sleeve floating, there’s no ground connection between the Xone and the Octatrack.
