Balanced and Unbalanced Signal

Balanced and Unbalanced

And how to turn one into the other


On Balanced, the signals being 180° apart enables you to summ them “loosing” the noise in the process.
Another plus for balanced is the fact the shield (= Ground/GND) does not carry any signal, it soley shields the signal from EMF.

That is all fine and good. Turning unbalanced to balanced is easily done using what is called a DI-Box.

The components in them varies, the concepts are super simple:

Op-Amp balanced (active balanced)
This circuit needs power (to feed the Op-Amps) and creates a “true” balanced signal.


A signal fed in from the left will cause each amplifier to “excite” a voltage in a different direction (180° phase shift).


Transformer balanced (passive balanced)
This method does not require external power, it soley relies on the way transformers behave.
passive_balanced
A current flowing in from the coil on the left generates current in the right coil, there magic (= physics) happens:
GND is the negative pole for the +
GND is also the plus pole for the -


You may now ask which one you should buy. I’ll answer that later.

But how do I turn a balanced signal into an unbalanced signal?

With transformer balanced DI-Boxes, you can just plug them in backwards. Simple as that!
balanced_unbalanced

But what to do when the stores have closed for the night and you realy need to hook up that one device?

If you look at the transformer balanced circuit again, + to GND is still a complete circuit.
So you can just hook + to Tip (or Pin on RCA), and - to Sleeve. (Or vice versa)


This however is a dirty bodge and you should feel bad for doing stopping at this!

So what to do with the floating ground?
Just soldering the loose pin in the XLR to Sleeve too will probably result in a nasty ground loop.

If you add essentially a low pass filter to the GND connection, it is mostly fine though. As powers are rather low, any 0.6W resistor will do. Capacitor is between 20nF and 5nF.

Congrats! You made your own Pseudo Balanced Cable!


That is great and all, but what DI-Box should I buy?

A big DEPENDS
The passive one will be a set-and-forget installation. For 80% of use cases, a passive one (~$20/20€) will be just fine! The GND-Lift can come in handy.
Active DI-Boxes often got small but helpful features such as attenuation, at the cost of having to change batteries or having to plug in a power adapter.

Am I in the 20%?

Probably not.

Lastly: Don’t spend 200 bucks on $40 worth of hardware. Physics stays the same for everyone!

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Addition:

The “what does what”-table:

Connector Signal L Signal R Signal !L Signal !R GND
2 pole jack “mono” :white_check_mark: :white_check_mark:
3 pole jack “stereo” :white_check_mark: :white_check_mark: :white_check_mark:
3-pin XLR :white_check_mark: :white_check_mark: :white_check_mark:
4-pin XLR :white_check_mark: :white_check_mark: :white_check_mark: :white_check_mark:
5-pin XLR DMX SIGNAL! DO NOT PLUG IN TO AUDIO GEAR!

As another note: 3 pin jack can also be used for balanced signal (common on mixers and audio interfaces. Then the pinout is T = Hot (Signal L), R = Cold (Signal !L), S = GND


Where is Ground on a headphone?
There is none.
A headphone has no grounding. At the powers involved, radio frequencies and other EMF is simply too weak to make a more-than-measureable difference. (When you can measure the difference, you are one step away from building a radio).

Balanced headphone pinouts:

4-pin XLR:
image

4-pole 2.5mm jack:
image

So, how do my headphones make sound without Ground?
Look at the first image in this thread again. When the signal is balanced, the signals are the inverse of another, meaning you have a voltage difference. A voltage difference will cause a current to flow. (Technically speaking, the lack of current causes voltage, different story).

Your headphone simply connects from the high of one signal to the low of another. This increased voltage is also the reason why balanced has more power (Power P = Voltage U x Current I), double the voltage, the power doubles too.

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