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Originally Posted by kwkarth
This whole idea of a "balanced" amp for headphones is a misnomer.
What we're really talking about IS dual mono. Whether or not it accepts a balanced input really is of no consequence in this application.
The Blockhead uses dual Max amps in a balanced push pull configuration to achieve double the headroom/output, but headphone drivers themselves in ALL cases, no exceptions whatsoever, are "unbalanced" devices. This also means nothing in the context for which a balanced system was developed.
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Note: I'm including some explanations of concepts that I know that you know, but I'm also trying to be comprehensible to others reading this thread.
"Balanced", in terms of headphones, may have originally been a misnomer, in that it referred to a different type of configuration and purpose than pro "balanced" gear, which is primarily used for noise reduction over long cable runs.
However, it is also very different from dual mono in the conventional sense as well. Dual mono would be two single-ended circuits, each with a hot lead and a ground, as long as the circuits were kept completely apart. Balanced headphone amps would have to be described as quad mono, except that doesn't quite fit either.
Push-pull traditionally involves a phase-splitter so that a given output device is not handling the entire waveform of the output. The actual output of a push-pull device is normally single-ended as far as the transducer is concerned, with the output of the push-pull devices combined to form the "signal". What we've got is something a bit different, as with four active channels, each output device is handling the entire waveform. If we attempted to combine these signals within the amplifier, as in a conventional push-pull device, we'd hear nothing but noise. By combining them at the transducer, they complement rather than cancel each other, with some effect on common mode noise as an almost incidental byproduct (reduction of common mode noise is the raison d'etre of balanced signals in pro audio).
Balanced headphone amps do provide a different kind of signal, as there is active amplification on both sides of the driver. Although the driver itself is not altered (electrostatics excepted, it makes no sense to call a headphone balanced or unbalanced, except as a reference to the type of connector attached), the nature of signal is indeed different in a balanced configuration. A + and - active signal is indeed different than a + signal and ground.
So, balanced headphone amps do not neatly fit into any of the existing categories. Since they use the same + and - signals as balanced pro gear (but drop the ground as unnecessary), "balanced" seems to be as good a terminology as any.