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Originally Posted by Koyaan I. Sqatsi /img/forum/go_quote.gif
Not necessary unless the amp's input will only accept a balanced input, in which case you'd need to use an adaptor or make an adaptor cable.
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No adapter needed.
If the input is "active balanced," which all modern inputs are, you can just drive one side.
If the input is balanced by the use of a transformer, which is the way it was done first in the phone company, then in broadcasting, then in sound reinforcement when tubes were in use, you have to ground the other side of the transformer, or at least tie it to the other side (ground) of the unbalanced feed.
Balanced inputs are only used for the common mode rejection. Any field cutting a wire will induce a small current. The longer the run, the greater the chance. If the field is induced in BOTH wires (as it will) of a balanced line, the common mode rejection of a transformer input will completely cancel the errant signal.
In the case of active balanced inputs, it will be nearly as good, based on the quality of the input stage.
Many active balanced inputs are done with only one op-amp. This stage will pretty much suck in the real world in situations where an actual balanced input is needed.
A real active balanced input requires a minimum of three op-amp stages. Still, to have the common mode rejection of an actual transformer, you need a servo circuit to actually --- well this gets to complicated to explain without drawing it. There are some recent patents on a way to apply this.
In a home, there is absolutely no reason for balanced interconnects. All it does is greatly increase the costs.
In a conventional broadcast facility, this can become important, but less so over time as technology progresses. Modern radio stations are being built around routers, so the audio doesn't go far making balanced audio overkill. (See router based mixing "console" systems by SAS, Sierra Automation Systems, and Harris Corp., or even Telos Systems.)
TV stations have been built around video routers for at least three decades. Hum on video is much more of a problem, yet unbalanced video is the standard. I have only seen balanced video used once, and that was when a video feed came from and AT&T microwave site, about a block to my site, and fed another, broadcaster owned micorwave transmitter. The only real reason to use balanced video in this case was because both sites were on different power feeds, and both on generator back-up systems. When one or both would go on generator, things could really go down hill without some sort of isolation.
In other words, balanced interconnects is a waste of money in a home situation.
From the output of the amp to the drivers in the headphones and argument COULD be made to keep them separate. HOWEVER, since most amps have pretty heavy ground returns, and most headphones have separate returns anyway, the chance of the IR losses causing a significant enough voltage to actually cause measurable, much less audible crosstalk is laughable.
But, if you use mono-blocks, and want to rewire your headphones so you cannot use them anywhere else without an adapter, go for it. You aren't going to make anything worse (unless you reverse the phase).
