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Topic: What does a balanced connection actually do and why have it on a headphone amp? (Read 1523 times) previous topic - next topic
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What does a balanced connection actually do and why have it on a headphone amp?

My (probably incorrect) understanding is that balanced (XLR) connections are used on microphones to reduce hum and interference over the cable, particularly on longer runs. How does that work (I can just Google it if no one want to explain)?

Given that, why do people state that xlr outputs on headphone amps are louder? Why would you want to use an xlr termination on a headphone cable with a max of a 10' run? How could be an improvement over the standard jacks, and why do most expensive headphone amps seem to have them?  Is it because the cable is often in motion on your body as you shift about, or rock back and forth as I do?
Music lover and recovering high end audiophile

Re: What does a balanced connection actually do and why have it on a headphone amp?

Reply #1 –
Hello BearcatSandor!
Good question - you know the advantages of a balanced connection for microphone input.
If you have a balanced headphone output and your device has four amplifiers (!) then they can work counter-phase, two amps for each channel. This doubles the output voltage and so quadruples the output power.
If you really need it louder, then this can be the solution. But you sure know that your ears do not like too much volume and once the hair cells are damaged, nothing can heal them ;)

Re: What does a balanced connection actually do and why have it on a headphone amp?

Reply #2 –
As Sunhillow pointed out balanced and balanced is two.

A balanced connection in the headphone world has nothing to do with a balanced connection as we know from connecting two pieces of gear e.g. a pre-amp and a power amp using a XLR.
XLR is a 3 wire connection, a hot, a cold and a common ground.
At the receiver there is a differential amp removing all common noise.

A headphone, having 2 wires for the left and 2 for the right, is identical to how we connect our speakers to an amp. Nothing “balanced” about this symmetrical connection but it does allow for amplifier topologies like indeed a balanced amp. That is why this single ended connection is called "balanced" in the headphone world.
TheWellTemperedComputer.com

Re: What does a balanced connection actually do and why have it on a headphone amp?

Reply #3 –
Quote
Given that, why do people state that xlr outputs on headphone amps are louder?
A normal signal has a signal-wire carrying an AC voltage that swings positive and negative, plus a ground.

A balanced connection has two signals with opposite polarity.   There is no ground (with balanced headphones).   All else being equal, that doubles the voltage across the load which also doubles the current for four times the power (wattage), and a 6dB increase.

A "regular" headphone shares a common connection (ground) between left & right so it won't work with a balanced-output.

Or, you could simply double the power supply voltage.

With power amplifiers (for speakers) this is called a "bridge" connection.  Some stereo power amps have a switch that inverts one channel to make a bridged mono-amplifier with double or 4-times the power.    (You don't always get 4 times the power if it can't supply the voltage and the current.)   The speaker is connected across the left & right "hot" outputs, so again there is no ground to the speaker. 

Some car amplifiers are made that way to get 4 times as much power as you normally get with 12V.   But real "high power" car amps have a DC-DC voltage booster built-in to boost the power supply voltage.

Quote
My (probably incorrect) understanding is that balanced (XLR) connections are used on microphones to reduce hum and interference over the cable, particularly on longer runs.
The same hum-noise is picked-up (in phase) by both wires.  The  audio signal is out-of-phase and the preamp has a differential amplifier where only the difference-voltage is amplified, and the common-mode noise is "canceled".    

It's more of an issue with microphone signals because any noise is going to be amplified, and the higher (but still "low") impedance means you get more noise pick-up.  With headphones & speakers you can't pick-up enough electrical noise-energy to be audible. 
 

Re: What does a balanced connection actually do and why have it on a headphone amp?

Reply #4 –
Thanks all! So to summarize what you're all saying: all of the ad copy about XLR headphone connections being better to reduce hum and interference is a misdirection because it doesn't apply to headphones anyway. It does provide a gain of +6db, but if you want that turn up your volume. If you actually need to boost it through XLR past what your volume control will do, you're probably damaging your hearing at that point or have the worlds most inefficient headphones.

Do I have that about right?
Music lover and recovering high end audiophile