Half or full normal is going to register continuity between upper and lower pairs of jacks. What you are looking for is to see if the signal ground is bussed on the patchbay (all jacks’ shield connections are tied together) or if they are isolated to each pair of upper and lower jacks. You checked both the signal conductor pin as well as the shield/signal ground conductor of the patchbay jacks, yes? And the upper and lower jack pairs are totally isolated to each other from the rest of the pairs? In your case that is probably best if that’s the case.
People do all sorts of things to deal with ground loop hum or improper system grounding resulting in noise induction…lift grounds, buy devices like noise filters, strap a small value cap in series with ground connections…I get it…sometimes you do what you have to do when it’s too hairy. I hope the noise filter works. But all of that is a band aid fix to either a design flaw in a device or an inconsistency in the application of signal ground theory between different devices in your array.
The bottom line is this:
If each device in your array of devices handles signal ground in the same way, and if each device’s ground plane is strapped to each other through a single path in order to eliminate any voltage differential between each device, and if each device has a proper ground scheme that doesn’t include any internal ground loops that induce noise, then hum and environmental noise induction should not be a problem. With a lot of help I completely reworked multiple facets of the ground scheme on a Soundtracs console I used to have. It was pretty jacked up all around. I had an AM radio station down the street and you could hear it loud and clear in every pathway. When the redesign was done, nothing…wonderful silence. I could even put my cell phone on a live call and set it right on the master section and open up every output and there was not one inkling of data chatter.
The big fat PITA is that it can be a major puzzle to investigate how each device’s manufacturer handled signal and chassis grounding (if signal ground references chassis ground…if the signal ground floats relative to the chassis we don’t care so much about the chassis, but then we have to pay attention to how the chassis references the building ground relative to the other devices in the array…and if the chassis floats also then there’s the potential safety issue…it’s all unfortunately complicated), and then beyond that another helping of PITA to get everything to align. Most the time we plug everything up, twist the key and hope it’s okay. Sometimes we twist the key and go “aw man wth…” Like you.
Most devices I’ve encountered are okay out of the box. But for me it’s part of getting to know a new device that enters my realm to open it up as soon as possible and look and see how they did it. Which usually also involves cross-referencing the schematics. But it is essential to look at the physical device to see how they handled signal grounding, and then the next step is to look for bad design issues that result in internal ground loops. What I’m going for is that each input and output jacks’ signal ground bonds to the chassis as close as possible to the jack, and that there is good positive bonding of the audio path 0V reference to the chassis, and then that the chassis is bonded to building ground through only one path. This avoids ground loops, offers a very low resistance path to ground for any noise, and ensures each device in the array is referencing the same ground reference through only one path. Again, most the time I open up a device to take a look and end up saying “good” or at least “that’ll work”, but in some cases I’m like “what were they thinking…” My Soundtracs MX-32 mixing console was a good example. But I think doing all that and knowing what to look for is understandably beyond most people and it’s only not so much for me because A. I’ve had some really nice smart people help me through some pretty exhaustive projects to correct issues, and B. I’ve studied the issue relative to my own array of gear and have enough of a grip on how things need to be to avoid the headaches. I’ve studied and had people teach me relative to a need to fix a problem. So I know what to look for now. It shouldn’t be so complicated. Manufacturers should be interested in making it simple for the end user. I think things have improved with time, but for those of us using devices manufactured across many decades, we are at risk of running into greater inconsistencies the further back in time we go with what gear we’re using.
For you, knowing you can connect a few fundamental devices and things are okay is a great start. And then from there do the add one thing in at a time until things go to pot and post some detail of what device it is, how it’s inputs and outputs are connected to other devices in your setup, like what devices and what type of connections, where and how the device is mounted, and what type of power connector it has.
