OT: mixing unblanced gear in a balanced patch bay

[Dave Labrecque]

Attic studio build on the horizon. I have four or five old ADC TT bays loomed out to punch-down blocks that I plan to install in an effort to over-engineer my dream home project studio. I have a few unbalanced outboard pieces I'd like to make available at the bays (Lexicon LXP-1, dbx half-rack stuff). Been doing a lot of reading on the best way to handle this. Getting mixed signals (see what I did there?).

Any sage advice welcome. I found an SOS article that mentioned creating a special patch cable that connected the unbalanced sleeve to the ring (cold or -) wire--I assume on the unbalanced cable end to make use of the balanced shielding. The guy didn't specify if that was for inputs or outputs. Maybe both? Downside (is it, though?) of this approach is a 12dB signal discrepancy/expectancy 'tween the two. (Also: wouldn't it make more sense to do this alteration/soldering at the connector to the unit itself, and then just use a normal patch cord at the bay?

I've also read about balancing all my unbalanced ins and outs using transformers (coloring the sound?) or op amps (noise? distortion?). I see ready-to-populate as well as fully-populated (except for a power supply) boards on Ebay for this purpose. But it's irritatingly hard to find noise and distortion specs to inform my buying decision if I were to go this route. Would love to find sufficiently-vetted, ready-to-solder kits.

Thoughts? Please and thank you.

[cgrafx]

Hi Dave,

Don't overthink this. Set aside a section of the patch bay for unbalanced gear, (meaning leave yourself a few extra spots for expansion), and just normalize the wiring of the patch bay for the unbalanced gear.

Don't keep different patch cables that will inevitably lead to plugging in the wrong cable in the wrong location.

What ever difference in gain between the balanced/unbalanced gear is irrelevant, as all of that will be normalized through the input/output gain knobs.

Adding transformers or OpAmp balance circuits to the inputs and outputs is not worth the time/effort.

Way more important to pay attention to ground loops.

[Dave Labrecque]

Thanks, Philip. I like what I'm hearing so far.

When you say "normalize," I don't suppose you mean as in "normaling" any of those connections? Because any of this unbalanced stuff will be patched into as-needed; no plans for any of it being part of a normal chain.

So what about interfacing the unbalanced with the balanced? For inputs and outputs? The best thing I've found is this page from my dbx 463x manual:



Which indicates that there are variations that may be needed depending on the specifics of the gear involved. Not ideal. Although, I suppose I could custom-wire the connections as needed at each piece of gear's in and out plugs.

Thoughts?

[cgrafx]

here is a really good article with diagrams

https://www.ranecommercial.com/kb_ar...p?article=2107

The most critical issue is going to be mitigating ground loops which unfortunately will depend on how each piece of outboard gear is designed (meaning, if needed, it will likely be different solutions for each piece of gear).

What I meant by normalizing was just to wire the patch bay connectors with the correct wiring for the unbalanced equipment. (probably should have used a different term as normalling actually has a specific meaning with patch bays.)

[jmh]

You might be able to just leave everything wired as balanced to and from the patchbay then you could use a t-s patch cable to bridge between the devices then always use an unbalanced cable to make the link to the unbalanced gear so that plugging in the cable shorts the ring to ground (using a t-s wouldn't be needed if that gear uses a trs female with the ring grounded).

I never remember the terminology of half, normal, and I think the tt have the little tip? But even if you can't get a t-s, you could modify a few trs by jumping the rs on on one end and mark them all with a color.

I'm still crawling under my desk to sort through cables and contemplating these things for myself. and it seems you always have the wrong gender when you have to patch line xlr to trs - and quoting Seinfeld: 'not that there is any thing wrong with that...'

In the short runs that you would have in a room studio the unbalanced picking up noise or even reducing the output of an balanced out by 6db isn't the concern but as Phillip pointed out it is grounding. PCs engineers don't have the same audio concerns so they are always a potential wrinkle - a re-patch might make that more noticeable.

I'm not an expert with patchbays and now I'm wondering when you have the setup where inserting a cable disconnects the default (through) patch, do they typically disconnect the tip, ring - and the sleeve?

[Dave Labrecque]

I'm not worried about noise getting into unbalanced runs so much, just want to be sure the sound gets through. These'll be short runs, with the gear close to the bay (I think).

In all typical normaling scenarios (including half- and double-normals), on the normal-breaking jack, both tip and ring are switched when a plug is inserted.

Good article (with pictures) at SOS here.

[Dave Labrecque]

here is a really good article with diagrams

https://www.ranecommercial.com/kb_ar...p?article=2107

The most critical issue is going to be mitigating ground loops which unfortunately will depend on how each piece of outboard gear is designed (meaning, if needed, it will likely be different solutions for each piece of gear).

What I meant by normalizing was just to wire the patch bay connectors with the correct wiring for the unbalanced equipment. (probably should have used a different term as normalling actually has a specific meaning with patch bays.)

Thanks for the link. Good stuff.

What do you mean by "wire the patch bay connectors with the correct wiring for the unbalanced equipment"? The patch bays are all TRS; unbalanced stuff, as you know, is TS (or RCA). Or do you mean follow Rane's suggestions on how to interface the two?

[cgrafx]

Thanks for the link. Good stuff.

What do you mean by "wire the patch bay connectors with the correct wiring for the unbalanced equipment"? The patch bays are all TRS; unbalanced stuff, as you know, is TS (or RCA). Or do you mean follow Rane's suggestions on how to interface the two?

Will depend on the patch bay, but if it's a wire soldered to the back, then you would specifically wire as TS, not TRS. Also you'll need to know if the sends and returns need to have the Ring grounded or can float. That will be specific to the interface being used for the sends/returns.

If the patch bay is TRS connectors then you would have to make TRS->TS and TS->TRS cables and you'd still need to know if the Send/Recieve interface needs to have the Ring grounded or can float.

[Dave Labrecque]

Will depend on the patch bay, but if it's a wire soldered to the back, then you would specifically wire as TS, not TRS. Also you'll need to know if the sends and returns need to have the Ring grounded or can float. That will be specific to the interface being used for the sends/returns.

If the patch bay is TRS connectors then you would have to make TRS->TS and TS->TRS cables and you'd still need to know if the Send/Recieve interface needs to have the Ring grounded or can float.

So it sounds like we're back to where I started, making up my own custom cables to use for unbalanced gear patching.

Since I need to consider the specific wiring on a by-device basis, and it's a TRS patch bay, is there any reason I can't do the custom wiring at the individual device I/O connectors or patch bay solder lugs (yes, they're that kind of bays)--depending on sleeve grounding preferences--and then use regular TRS patch cables for all patching?

[cgrafx]

So it sounds like we're back to where I started, making up my own custom cables to use for unbalanced gear patching.

Since I need to consider the specific wiring on a by-device basis, and it's a TRS patch bay, is there any reason I can't do the custom wiring at the individual device I/O connectors or patch bay solder lugs (yes, they're that kind of bays)--depending on sleeve grounding preferences--and then use regular TRS patch cables for all patching?

Yes, I was specifically suggesting doing the custom wiring at the individual device patch bay solder lugs but could also be on the individual device connectors.

Yes, all patch cables will be TRS.