What are the benefits or non-benefits of using balanced lines?

I have balanced input and output on my pre-amp and have often wondered this question as I did try them once and heard absolutely no sonic improvements.

 

Dave,

You should have heard the level drop though. Can't remember if it's 3dB or 6dB.

Regards,
Metralla

 

Steve or anyone,

I've seen balanced lines a lot and is there any practicle application?

 

Dave,

The textbook (sophamore electronics) answer to your question is: balanced interconnects are more immune to noise. A differential pair amplifies the difference of balanced signals on the + and - lines with a much higher gain than it does the common mode signal (think of it as the signal that appears on both lines, or mathematically their average). The ratio of the two gains is called common-mode rejection ratio, which can easily exceed 70 dB. Your preamp outputs a pair of 180 degree out of phase signals at its balanced outputs. Any noise that couples into both lines appears as a common-mode signal at the inputs of the differential amplifier in your power amp. You can simply think of the noise being added to both the + and - lines and gets cancelled out when the differential signal is amplified.

Does unbalanced always sound better balanced? Unless you have a balanced audio signal to begin with (in most cases you don't), the unbalanced signal has to be converted into a balanced one by a single-ended-to-differentail converter so at least one active stage is added to the signal path. This is why unbalanced sounds more musical, in Steve's words.

So use the balanced interconnects only if your gears are close to electromagnetic noise sources (e.g. Yoko), or you have balanced sources and a fully balanced pre-amp.

 

Only if the balanced (differential) signal is converted back to single-ended will you lose half of the voltage swing (i.e. 6 dB drop), assuming the two signal paths are matched.

 

Paul,

I could hook up balanced as my preamp does have both input and output balanced lines but, if there's no sonic benefit, never mind degredation, why bother.

 

A fully balanced preamp? How many gold records (in RIAA's term) did you put out? Well, it could be either fully balanced or faked (balanced -> single-ended -> balanced). Like I said, you've got to feed it with balanced sources too. And don't for a minute believe that your CD player has one. The DAC has to be balanced too.

 

Paul,

Nope my cd player doesn't, but I have seen ones that are.

 

It doesn't mean a thing even if a CD player or an outboard DAC has balanced outputs. The outputs of the D/A converter IC inside have to be balanced as well. Then you have something balanced to begin with.

Don't forget the "fake" balanced amps with balanced I/O but single-ended signal paths. Why are such products made? The manufacturers want to sell them to the uninitiated customers at premium prices without taking a hit on the higher costs of fully balanced designs. Fully balanced means two signal paths per channel, as opposed to one per in single-ended plus B-to-U & U-to-B converters.