A couple things…
I agree, as a general practice, it’s best to avoid putting your mic inputs on a patchbay, at least avoid putting it on a patchbay shared by anything other than the mic inputs, and this is because of the aforementioned presence of phantom power. Now I realize the 388 doesn’t have phantom power, but I just wanted to plop that here for the general reader whose device might have phantom power. And I never understood what the need was to put mic inputs on a patchbay anyway. Mine are on a snake with a stage box. You might have yours on a snake with a fan or maybe the snake terminates in a wall panel. Whatever. My point is usually the need is simply being able to access the mic inputs and your “patching” is plugging and unplugging what mic needs to go to which input on your stage box/fan/wall panel. Hopefully that makes sense. But if your mic inputs have phantom power it’s just best not put those on a patchbay with other input types like line level because if you screw up and patch a line source to a mic input with phantom power engaged you will likely zorch your line source.
Another comment…balanced audio and ground loops…I think it is 1. incorrect and 2. even haphazard to draw a connection or otherwise assume there is a direct correlation to balanced audio and the elimination of ground loops. And I speak from the vantage point of having done my own deep dives into modifying the ground schemes of several larger consoles and also many smaller audio devices, and working through the processes of aligning the entire ground scheme of my setup, which includes a console with a total of 128 inputs, not including the insert points, and about 80 rack units of outboard processors and recording devices, and all of it connected to six 96-point TT patchbays. It’s been an interesting type of hell. BUT…this has all been supported by doing a lot of reading, asking A LOT of questions, actually tearing apart large consoles and analyzing how the audio system grounding is designed throughout the whole console, and ahead of ALL of this and throughout the console projects being mentored/coached directly by people who know a lot more than me, and primarily by a gentleman who wrote a widely referenced paper on audio system grounding and the “pin 1 problem”, the late great Neil Muncy.
Balancing audio signal is intended for the purpose of mitigating induced noise interference…radio and other ultra-high-frequency environmental noise. It was developed many decades ago by the telephone industry because, you betcha, signal lines hundreds and thousands of miles long can induce unwanted noise. But if you have a ground loop and the hum associated with it, balancing that signal is not necessarily going to fix your pin 1 problem. That has to be mitigated in other ways after careful analysis.
For you, I wouldn’t over-think it. If your cable runs are 20 feet or so or less, and you have outboard gear that can handle both balanced and unbalanced sources and loads, don’t worry about balancing your unbalanced sources and loads to that equipment just because that outboard gear *can* accommodate balanced sources and loads. Use good quality shielded cable, and only worry about balancing signals to outboard gear that can only accommodate balanced sources and loads…and that’s rare. I know you have a compressor that appears to be that way. But in general read the manuals to your gear. I have a number of devices that appear to have only balanced interconnections, but the manuals all have specific instructions for how to interface unbalanced gear. Sometimes these details are important (like to avoid noise problems or even avoid damaging equipment). As they say, RTFM. But if I was you, since your console is largely unbalanced (except for the mic inputs and balanced main outputs), I would just use unbalanced cable runs and patchbays. There’s no reason you can’t use a balanced patchbay, but understand, even if you run balanced cabling between the patchbay and devices with balanced interconnections, as soon as you patch a balanced input or output to an unbalanced source or load, the balanced input or output is now unbalanced anyway…there’s nothing connected to the parallel inverted input (or, depending on your cabling, the parallel inverted input is now connected to signal ground). I would just keep your cable runs short, use good quality cable, and wire things up and see where you are at…use the LA-40 in cases where balanced input/output is your only option for a given device. If you have hum problems those are going to have to be teased out by analyzing how each device is connected to building ground (or if there are cases where the chassis ground is floating)…basically figuring out if or how all devices chassis are grounded and how they connect to each other…ideally every devices chassis is connected to the ground pin of its grounded power cord and everything connects to the building ground on the same circuit…that’s step 1. And I know you have devices with only two-wire non-grounded power cords. So that’s fun. In my case I modified everything in that category. And THEN the next step is to figure out how the SIGNAL ground in each device connects to the chassis ground. And that is the “pin 1 problem” and the source of most signal ground issues in an audio environment. Some devices follow best practices and others most certainly do not. But don’t go rabbit trailing on this. Hook things up…short cable runs…good quality cable…see where you’re at. You also have to be mindful of how the signal grounds are handled in the patchbays…they might be bussed…they might not. And this can be a problem. But hook things up and see where you’re at.
FWIW I went balanced on everything in my space, but that was driven by the fact everything is balanced on my console (and in fact signal is balanced all the way through the signal pathways on my console…it is balanced internally as well as at the inputs and outputs), and most everything outboard is balance-capable, so I decided to keep everything that way based on my own past experience dealing with noise interference. I used to live really close to a high-power AM radio station, which is what spurred my journey into all the audio system grounding learning and projects. That’s not the environment now, but old habits are hard to break.
