- Jan 16, 2011
I see some confusion here, and would like to help you understanding some amplification concepts.
SE, just as the acronym says, is Single Ended. The cable would most often be RCA for two poles - signal and ground.
Balanced means that the signal is transferred by cable via 3 poles: signal in phase, signal in opposite phase, and ground.
I guess everyone by now knows what a SE amplifier is - single output device (tube, usually, but not necessarily): a balanced connection to this type of amp would be redundant or superfluous, either only one of the signal phases would be used, or a differential amplifier would be needed to sum the two signals.
Now if you know what an SE amplifier is, you probably know what a Push-Pull amplifier is: two devices working together to drive a load. A balanced connection would be beneficial for a PP amplifier, because it could do without a phase splitter. But, as a matter of fact, PP amps (particularly tube amps) with balanced inputs are quite rare.
Obviously, a Push-Pull amplifier is balanced by design, yet it usually does not have a balanced input: the signal passes through a phase splitter and the missing component - inverted phase (opposite phase) is created.
In the same fashion, most headphones amplifiers with balanced outputs do not have balanced inputs. The point of having a balanced output is having 4x the output power compared to the SE output stage, while actually having just 2 SE output stages working in opposite phase, with ground connections separated between channels (the ground connections to the headphones are omitted and the two connectors of each channel are directly connected to the amplified signal and the amplified opposite phase signal.
I would like to add that balanced cable connections between HiFi equipment components are more a marketing hype than a real advantage. Balanced connections have much improved Common Mode Rejection Ratio, but if the signal is large enough (line level), and the cables are shorter than 2 meters, the resulting improvement in CMRR is negligible in practice.