Balance ??

I want to understand (in layman's terms) what the term "balanced" means. I see amplifiers with balanced outputs and balanced interconnects. Do all amplifiers have balanced imputs ?? Do you need special digital source equipment with balanced outputs ?? Is this different from a "digital" connection ?? Help !! and Thanks
Not all amplifiers, not even all good modern ones, have balanced inputs. Pass Aleph 3, for example, doesn't. Not all digital sources have balanced outputs. Likewise not all preamps: the CAT's are an example. A balanced circuit involves doubling a lot of signal path components, and the CAT designer thinks money is better spent otherwise. One advantage of balanced is that you can use XLR connectors, where, arguably, the cheapest are better than the most expensive RCA's. Ability to use long interconnects is another virtue of balanced. I'm sure others will tell you more, but these are some fundamentals, as I understand it.
O.K., your audio signal is nothing but a wave (Dude!) with a positive cycle and a negative cycle... with me so far? Anyway, imajine spliting off the positive part and sending it to amplifier "A" and likewise sending the negative part to amp "B" (there are actually two amps for each channel which is why Balanced costs more). Onward... Now that you have the two halves isolated, you compare them to each other (the ground-wire value is used somehow as a reference. ever notice balanced interconects have 3 wires?) with the understanding that they should be complete opposites. If anything is found in common, it is assumed to be hum or noise of some kind and stopped dead in its tracks (does not get out of the amp). The result is a very quiet background for your music (Shazam)!
A balanced interface, whether low-level (interconnect) or high-level (amp output) means that there is no signal-ground reference. When a differential signal swings positive on one leg it is simultaneously swinging negative on the other leg. Ground is used only for shielding & does not carry either leg of the signal. Advantages are noise-immunity esp. with longer interconnects, and 6dB greater signal level than unbalanced. My full-balanced power amp. is dead quiet, compared to the very low-level noise of another amp which is unbalanced. Cost is a factor in balanced designs because there are more electronics involved. No need for any 'special' sources. Digital outputs (from a CD player) may be either unbal. or bal. just as analog connections can be done either way. An industry standard impedance for bal. is 600 ohm, vs. unbal. interfaces which vary.
[email protected] : great post. you b the dude! now, can u 'splain the jitter differentials in sacd v. dvd-a?
So, my follow up question is that if you have a choice between rca's and a balanced interconnect, then the balanced choice is a "no brainer", then, right ??
Actually, balanced circuits have nothing to do with signal symmetry. Rather, it refers to the balancing of the common mode impedances. In a balanced circuit, the signal is not bound to be symmetrical around an arbitrary point (like ground) but will be divided according to the mismatch of resultant generator / load impedances. Further, there is no obligation to have a higher output level, though this might result with some topologies. This subject is rather basic, yet in the audiophile community there seems to be a great deal of misunderstanding. Consider a phono cartridge. This is a nearly perfect balanced generator, yet defies the definition of a "three wire circuit". None-the-less, you would be hard pressed to define a better balanced generator (nearly perfectly balanced common mode impedance). In a more "typical" configuration where a source is driving a load the advantage of a balanced circuit is in its ability to reject common mode signals. The amount of rejection is defined as CMRR (common mode rejection ratio) and it is typically expressed in dB below the differential level. Here, the impedance balance of the generator and load will affect the CMRR. While it is true that an XLR connector is the standard for use in balanced audio circuits, it should be noted that it is not the connector that makes a device balanced and that balanced is not an absolute term. One product can be much more balanced than another. Kevin Halverson