Passive split with a balanced patch bay and balanced and unbalanced connections

dooper

Member
2004-01-12 4:40 am
Canada
I'm mixing pro and prosumer/semi-pro equipment and want the results to be as good as they can be.

I want to take the balanced direct outputs from 24 channels on a Soundcraft Series FIVE console and split them using an ART P48 balanced patch bay as shown in the attachment.

The first signal destination is a Cymatic Audio uTrack24 recorder which has 24 balanced inputs on DB25 connectors using the TASCAM standard. No problem so far - all of the connections and cables are balanced.

The second signal destination is an Allen and Heath ICE-16 recorder which has 16 unbalanced 1/4" TS inputs. This will be my backup recorder and I will obviously not be able to capture all 24 mixer channels on the 16-track recorder.

I don't want to use TS/unbalanced cabling from the patch bay to the ICE-16 so I had an idea to use these adapters.

I have two 8-channel RCA-M to TS-M snakes and I can use these to pull hot and ground from each adapter to the ICE-16 recorder without tying hot and cold together on the balanced signals coming from the mixer.

The uTrack24 is not here yet so I will not be able to test for a few days.

What I am wondering is will I muck up the balanced connection from mixer to uTrack24 by splitting the signal in this manner? Thanks for any and all knowledge!
 

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I don't want to use TS/unbalanced cabling from the patch bay to the ICE-16 so I had an idea to use these adapters.

Each RCA connector on that adaptor branches out to one side of the balanced signal... one is connected to the tip, the other to the ring, both rca grounds should be tied to the sleeve... so yes it should work.
 
Thanks Douglas. What I’m wondering though is will I upset the balance of the connection by feeding hot to both sides of the split while only feeding cold to one of the two sides of the split. If this was water the pressures would not be even. How do electrons behave?

Like water ... they go wherever the voltage pressure sends them.

But, a long time ago engineers figured out that impedance matching had the downside you're fussing over... two inputs on one output could be a problem. So they came up with Impedance Bridging to address the problem.

Basically the modern scheme is that each output has a low impedance, usually around 100 ohms or less. Then each input has a much higher impedance, typically 10k or higher. In this way any line level output can drive any line level input without fear of signal degradation. In fact it can usually drive several inputs without serious consequences.

The actual current in an RCA cable is minimal... Figure 2 volts at 10k ... Ohm's law tells us that is 2 / 10,000 == 0.0002 amps or about 200 microamps... So, it's mostly a voltage thing, power in microwatts.

With your splitter setup you will have a tiny impact on the hot signal but as long as you aren't dumping into a half dozen or more splitters and/or very long patch cords you'll be fine. Any pro-audio system with a good XLR receiver at it's input should easily be able to cope with it.
 
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dooper

Member
2004-01-12 4:40 am
Canada
I did my first run last Saturday evening and everything worked as expected. The recording levels on the unbalanced recorder are a bit lower than the levels on the balanced recorder. I will take a closer look at the WAV files this evening and come back with the exact difference between the levels. Till then, cheers!
 
Each RCA connector on that adaptor branches out to one side of the balanced signal... one is connected to the tip, the other to the ring, both rca grounds should be tied to the sleeve... so yes it should work.
Well it might work.
But if the output stage is a transformer, it won't work.
and if the output stage is a passive/impedance one. Then only one of the lines will work.
 
Results: Track 16 on both machines is a mono sum of the front-of-house mix from the Soundcraft console. I loaded track 16 from the first song of the first set from both machines and compared them. In Audacity for Windows, the loudest peak in the file that was recorded on the balanced uTrack24 machine measured -18.102dB and the loudest peak recorded on the unbalanced ICE-16 machine measured -24.201dB. The difference, for all intents and purposes, is 6dB which is what you would expect it to be.