Impedence Balanced Connections

[SteveECrane]

Hello lovely people!

Short version of my question:

Should I treat Impedance Balanced Connections in exactly the same way as actual balanced connections (whether transformer or electronically balanced)?

Longer version of said question:-

I have a couple of Behringer RX1602 line level mixers which I've always connected directly to all my synth gear (or via the odd pedal or two) and then onto a FoH or studio mixer, either via a DI box (Radial JPC or Behringer DI800 / DI4000) or simply via a couple of mono TR cables in the studio, if the runs were short enough.

Because I'm finally dumping my Behringer MX9000 desk (it's started to play up a bit too much - failing channels and failing routing - and takes up too much studio real estate these days, given my own composing/playing needs) I decided to patch the RX1602's into the Behringer PX3000 (balanced) patchbays (patch-bay? Hyphenated?) so I can add in effects pedals and other such goodies at a whim.

However, I'd always thought of the Main Outs on the RX1602 as (TR mono jack) unbalanced outputs ... but I consulted the manual and it stated TRS jacks. "Hmmmm, that's a l'il bit weird", I thought! This got me thinking. I initially suspected a misprint as the spec sheet at the rear of the manual clearly said the outputs were unbalanced ... and that's how I'd used them in the past, without much trouble.

Nevertheless, a bit of digging around online mentioned something called "impedance balanced" - it's in the RX1602 v2 manual spec sheet at the rear of the 'new' User Guide - which I'd never heard of. It seems it was something of a marketing ploy by Mackie in their early days, something which Behringer (unsurprisingly) 'borrowed' as it has some definite signal transfer benefits. Unfortunately, I'm finding it hard to separate the fact from the BS and understand precisely what the benefits (and downsides, if any) are! It also means I'm unsure how to connect it to the patchbay.

That's where you wonderful people come in...

There's a lot of jibberish concerning this online - marketing hyperbole, sales rhetoric, amateur opinion, guesswork, etc. - so I thought I'd seek a definitive clarification from the one-and-only expert on all such matters, namely Mr Robjohns!

More seriously, what I would like to know is whether I should connect these RX1602 sub-mixers to my patchbay using stereo TRS balanced interconnect cables or via the mono TR leads I've used in the past?

I try to use balanced cables/connections everywhere I can to alleviate any common mode noise but what I don't wish to do here is introduce any future problems (it took aeons to remove all ground loops from my setup years ago) by making any 'common sense' assumptions based on my obvious ignorance.


So, any and all help appreciated!

Thanks in advance,

Steve.

Pages 12 and 18, if anyone's interested:

https://mediadl.musictribe.com/media/PL ... 602_WW.pdf

and the patchbay:

https://mediadl.musictribe.com/media/sy ... 673246.pdf

[James Perrett]

If they are feeding balanced inputs then you might as well treat them as balanced outputs and use balanced cables everywhere. You will gain all the interference rejection advantages of balanced connections.

[Hugh Robjohns]

Short version of my question:

Should I treat Impedance Balanced Connections in exactly the same way as actual balanced connections (whether transformer or electronically balanced)?

Short version of my answer:

YES

Mind-numbingly longer version:

ALL balanced interfaces are impedance-balanced because having matched (hence balanced) impedances to ground is what allows them to reject interference... which is their whole raison d'etre.

So the 'balanced-impedance' name is a really poor and confusing one that doesn't actually describe the true nature of whats going on at all... but we're stuck with it.

The ONLY difference between what you describe as an "actual balanced output (transformer or electronically balanced)" and an impedance-balanced output is signal symmetry (or its absence).

I prefer to use the terms, symmetrical and asymmetrical balanced interfaces.

A symmetrical balanced output (transformer or electronically balanced) conveys half the signal voltage on the hot side of the connection, and half (polarity inverted) on the cold side. This is the classic view with equal and opposite waveforms...

An asymmetrical balanced output (impedance-balanced) conveys the entire signal voltage on the hot side only, with nothing (other than the signal voltage reference) on the cold side.

All receiving balanced inputs — whether electronic or transformer — effectively look for the signal voltage between the hot and cold sides: = Hot –Cold.

Let's call the signal voltage V.

The asymmetrical format is thus sending V on the hot side and nothing on the cold, so = V – 0 = V. Thus, the output from the balanced receiver is the whole signal, V.

The symmetrical format is sending half the voltage on each side, with the cold side inverted. So = V/2 – (–V/2)
Which can be simplified to = V/2+V/2
Which is = 2V/2
Which is = V

In other words, both systems deliver exactly the same signal.

And because both systems have matched impedances to ground from each side, any external interference generates identical voltages (let's call it U) on each side. So, as the balanced receiver is looking for = Hot – Cold
Interferencec = U– U = 0

... the interference cancelled out. Hurrah!

As you can hopefully see, both symmetrical and asymmetrical interfaces work in exactly the same way, do exactly the same thing, and should be used in exactly the same way.

Naturally there are some technical differences between the two formats that benefit different situations and applications, but that's the icing on the cake, rather than the cake itself and 90% of the time such technicalities are irrelevant... but if you want to know, a basic comparison is:

1. Transformer balanced outputs generally provide the best rejection of RF interference, prevent ground-loops, and deliver the full signal level to both balanced and unbalanced destinations. They can also be configured to boost the output level, giving the electronics greater internal headroom.

Against those benefits, they are also expensive, bulky, heavy, can introduce distortion, and are prone to picking up hum from mains transformers.

2. Electronically balanced outputs are inherently much cheaper, smaller, lighter, with lower colouration. But against that some designs are very fussy about how they are wired to feed unbalanced destinations, and only deliver half the signal voltage.

3. Impedance balanced outputs are slightly cheaper still, and smaller, and they are unfazed whether feeding balanced or unbalanced destinations, both receiving the same signal level. But some designs are less effective at rejecting RF interference, and they all have 6dB less headroom than an electronically balanced output.

There's a lot of jibberish concerning this online - marketing hyperbole, sales rhetoric, amateur opinion, guesswork, etc. - so I thought I'd seek a definitive clarification from the one-and-only expert on all such matters, namely Mr Robjohns!

There is a lot of jibberish and nonsense uttered in fora and marketing blurb.. and you've just had my clarification

There's more with diagrams here: https://www.soundonsound.com/sound-advi ... -balancing

More seriously, what I would like to know is whether I should connect these RX1602 sub-mixers to my patchbay using stereo TRS balanced interconnect cables or via the mono TR leads I've used in the past?

Balanced TRS is definitely preferable, giving the best of both worlds and supporting optimal connections to both balanced and unbalanced gear.

...what I don't wish to do here is introduce any future problems (it took aeons to remove all ground loops from my setup years ago)...

Ground loops are always a risk when connecting unbalanced equipment, but at least if you use TRS cables you shouldn't have that problem when patching to balanced destinations.

[SteveECrane]

Hugh,
I really would like to say more than a simple "Thank you" as these words just doesn't (ever) seem sufficient given the quality of the responses that you always provide.
I'm reasonably literate as far as analogue electronics is concerned but your responses have a focus, brevity and clarity that only an expert with real-world experience - that can actually teach - can deliver.
You really should write a book ... or update an existing one to include more of these techy tidbits!
So ... thank you.
Damnit!
Steve.

PS For anyone who's reading this, you should buy this: https://www.amazon.co.uk/gp/product/0415823862/

Updated link. The original led to a 'page not found' error -- ED.

[ef37a]

Can I just add that another useful property of 'impedance' balanced outputs apart from reduced cost is that it is impossible to reverse the polarity of the signal. Get it wrong and you get nowt.

To add to the above, anyone building a system using balanced connections would do well to make up a simple TRS in/out box with a P flip switch to check polarity 'as you go'.

Dave.

[Hugh Robjohns]

Can I just add that another useful property of 'impedance' balanced outputs apart from reduced cost is that it is impossible to reverse the polarity of the signal. Get it wrong and you get nowt.

Hmmmm..... You can most definitely reverse the polarity of the signal if feeding a balanced input! Just swap the hot and cold lines. Voila! Upside down output.

But if you wire the cold side to an unbalanced input you do, indeed, get nowt.

[Hugh Robjohns]

Hugh,
I really would like to say more than a simple "Thank you" as these words just doesn't (ever) seem sufficient given the quality of the responses that you always provide.

Thanks Steve, I appreciate that.