Amplifiers

[richteer]

Originally Posted by MatrixS2000

Those are balanced inputs. Most people are familar with unbalanced RCA connections where the postive signal is on the centre post and the negative is on the sleeve. Balanced connectors have 3 connections. A +, - and ground. It's advantage is that it can carry a higher level signal and that an amp with balanced input should not have any hum.

Close, but not quite accurate. Single-ended (normal) connections have two signals: +ive and ground. These type of connection can be susceptible to RFI (radio frequency interferance); the longer the cable and/or more electrically noisy the environment, the worse the problem will potentially be.

In a balanced connection, the audio signal mirrored, the original signal using the + connection and its mirror using the - side (the ground is used in the same way it is in single-ended connections). Each of the signal cables is susceptible to RFI in the same manner as single-ended connections, but because the two halves of the signal are 180 degrees out of phase with each other, the induced noise sums to zero. (This is a bit hard to explain with drawing a picture!)

The signal in a balanced connection isn't necessarily a higher level one than that found in single-ended connetions, I guess hum might still be an issue.