Splitting line level balanced mic preamp output signal, cable wiring, trs vs ts

[cashhewn]

I was reading Hugh’s article on various methods for splitting a mic signal (https://www.soundonsound.com/sound-advi ... mic-signal) and had some questions about the wiring of a passive Y-cable to split the line level output from a microphone preamp balanced output:

I see available both TRS to dual TS cables as well as TRS to dual TRS cables, and I don’t understand the actual wiring of the latter (maybe not even the former!).

What are the implications of choosing one over the other for splitting the line level output of a balanced microphone preamp (the goal here is if a client asks me to split the signal to record both “straight to the converter” and also through the analog path of the desk)?

Many thanks.

[James Perrett]

I see available both TRS to dual TS cables as well as TRS to dual TRS cables, and I don’t understand the actual wiring of the latter (maybe not even the former!).

The first cable is for splitting a stereo signal into two mono signals - or for use with an unbalanced insert point. The second one is probably the one you need to send one output into two inputs (assuming it is wired pin to pin).

[Wonks]

You certainly need TRS to TRS if you are keeping the signal balanced.

What you might need is the sleeve connection lifted at one (or two) ends of the cable if you experience any ground loop noise.

The output impedance of the mic preamp will be low (say 100-600 ohms or less and generally at the low end on modern equipment), and the the input impedance of balanced line inputs is typically between 10k-56k. So splitting a line output signal should be possible to at least 4 devices without loading up the line output (using the input impedance >= 10 x output impedance rule of thumb).

[Hugh Robjohns]

...some questions about the wiring of a passive Y-cable to split the line level output from a microphone preamp balanced output

It's easy to passive-split line-level signals because standard line outputs and inputs are built with exactly that in mind.

In a studio situation it would normally be done using a 'mult' in a patchbay where three or more sockets are wired together — all tips linked together, all rings wired together and (usually but not always) all sleeves wired together.

In that way the balanced output from a source is shared across any and all balanced destinations plugged into the connected sockets.

You can achieve the same thing with a splitter cable by wiring two balanced output leads onto one balanced input lead. Tips to tips rings to rings, sleeves to sleeves.... although it can be tricky to get two balanced cables into a TRS plug!

I see available both TRS to dual TS cables as well as TRS to dual TRS cables, and I don’t understand the actual wiring of the latter (maybe not even the former!).

TRS to dual-TS is intended as either a stereo to separate left/right conversion (eg, from a headphone output) or, more usually, as an insert cable, designed to access the unbalanced send and return from a mixer channel.

One TS carries the unbalanced send from the TRS tip/sleeve, while the other carries the unbalanced return to the TRS ring/sleeve.

If you tried to use that sort of cable to split a balanced output, you'd get very different results depending on the nature of the output circuitry.

A symmetrical electronically balanced output would give an unbalanced signal on one TS plug, but 6dB low in level. The same would appear on the other TS plug, but with opposite polarity.

An impedance-balanced output would give a full level signal on one TS plug, and nothing on the other.

And a floating transformer output would either give the same results as the symmetrical output, or nothing at all, depending on balanced input and grounding arrangements!

....so dont use a TRS to dual-TS for splitting a balanced output!!!

I would assume that a TRS to dual-TRS cable is wired in parallel, tips to tips, rings to rings, and sleeves to sleeves... in which case it would be perfect for splitting a balanced line signal.

You can also buy line splitter boxes, which I much prefer to use. These are usually just a bunch of sockets wired together in a box (beware, some have transformers to isolate as well as split the outputs).

Decades ago I made a couple of two-channel splitter boxes using a Canford extruded case:

https://www.canford.co.uk/CANFORD-UNIVE ... UDED-BOXES

Just fit one female and two male XLRs (or three TRS sockets) to each side, and wire each set together for two channels of 1 into 2 splits.

If you're feeling frisky, fit a miniature toggle switch on each side to lift the ground of one output to break ground-loops.

Or you also can buy ready-made 1 to 2 XLR splitters here, or buy the empty box and fit your own choice of connectors:

https://www.canford.co.uk/CANFORD-UNIVE ... ER-T-PIECE

Canford have all manner of connectors available as d-type chassis that just drop in.

I use several of these hexagonal boxes for 5-pin to dual 3-pin break out boxes for stereo cables, for example.

[cashhewn]

James, Wonks, Hugh: Thank you gents so much, this is exactly the thorough information I was looking for!

A symmetrical electronically balanced output would give an unbalanced signal on one TS plug, but 6dB low in level. The same would appear on the other TS plug, but with opposite polarity.

Great to point this out since it had not occurred to me, but of course they would be opposite polarity due to the nature of how balanced circuitry eliminates noise.

In any case: TRS to multiple TRS for me then.

And many thanks for the links, and for the super handy suggestion of building a splitter box myself and putting the audio ground lift on a switch, fancy!

I've said it before but SoS is priceless to me in lieu of having physical access to experienced engineer mentors.

Good stuff chaps and thanks again!