What is balanced input/output in regards to factory head unit/ aftermarket amp?

Hello,

I'm taking my time and researching upgrading my stereo. I have a non HK system.

I have the NAV so I don't want to change my head unit, so I’ve noticed the best way to go as far as an amp is one that will accept a balanced input. What does that mean and what amp should I get? I don't want to get screwed by my local radio shop!

By the way all I want to add is new speakers all around. I'll probably not add a SUB if the only place I can put it is in the trunk.

Thanks for the Help!

Grabbed from http://www.gainesaudio.com/faq.htm :

What's a balanced line interface, and where would I use one?

A balanced line interface is a go-between that allows audio products which have differing input/output standards to talk to each other. For example, the CD player in your home stereo system might have an unbalanced RCA output operating at a nominal signal level of -20 dBV and with an output impedance of 1,000 ohms. That's fine if you're connecting it to another piece of equipment - say, your home stereo receiver - that's talking the same language. However, if you try to connect that same CD player to a professional mixing console that's expecting a balanced line operating at a nominal signal level of +4 dBV and with a 600 ohm source impedance, the results may not be what you hoped for. You might experience noise, high frequency loss, or distortion. A proper interface assures that consumer (or semi-pro) gear will be a good match for professional equipment.
What's a balanced line anyway?

An unbalanced audio line uses two wires to make a connection: hot (signal) and ground. A balanced line uses three wires to make the same connection: signal plus (+), signal minus (-), and shield (ground). Because the signal lines are independent of the shield, you have more flexibility in determining how the shield is connected - or not connected - and a better chance of eliminating ground loops (ground what? Don't worry, we'll get to that) and hum. If that balanced line is then connected to equipment with a balanced input, noise induced into the cable is greatly reduced, resulting in the highest quality transmission from your source to your destination. That's why balanced lines are the standard in all broadcast and professional audio installations.

So basically a balanced output from a headunit theoretically gives a much cleaner signal than an unbalanced one. Higher end amps like Xtant and JL Audio accept balanced inputs.

I just did an audio upgrade for my 1999 323i. I also read up on the balanced differential signals coming from our oem head unit to the oem amp. I installed a Kicker KX600.4 amp that takes RCA and speaker level inputs. The amp took my inputs directly from my head unit (I intercepted them in the trunk just upstream of my stock amp). But, I am experiencing faint alternator whine on my system now. I ordered the Peripheral Vendetta http://store.autotoys.com/cgi-bin/wfp53024.storefront which is suppose to convert the balanced signal to unbalanced. This should cure my noise problem since I did verify that my noise is coming in from my inputs to the amp.............I will let you know how it goes after I install it. I would think that a higher end amp like the ones you mentioned that acept the balanced signals would not have this noise.

I installed the Peripheral Ven4 differential line converter and that took care of my alternator whine noise on my system.

Thanks for the info. I will look into getting a JL audio or A/D/S Amp in the comming weeks. Thanks again!!!!