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Старый 14.04.2011, 21:02   #23
Serge44
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http://www.headphone.com/learning-ce...y-balanced.php
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What's the Difference Between Balanced Transmission and a HeadRoom Fully Balanced Headphone System?



The most common use of balanced audio signal transmission has actually little to do with driving headphones in balanced mode. In many professional audio applications, signals are routed from place to place via balanced cables in an effort to reduce common mode interference from radio frequency (RF) noise sources like fluorescent lights and motors. Because the voltage developed on the transmission line from RF interference is identical on both normal and inverted signal conductors, and because the balancing transformers only allow current flow when the signals are opposing, the common interference signal is cancelled out (fig.1). This problem is not typically an issue even with single-ended headphones because the low output impedance of the power amp prevents a significant RF interference noise voltage from ever developing. But there are other excellent reasons to drive headphones with a particular type of balanced amplifier.Certainly, there are a number of amplifier designs that are single-ended internally, but use transformer coupled outputs (fig.2); these amplifiers improve headphone performance largely because of the removal of the common ground.



However, there is an entirely different approach that can be used to get significant and measurable performance improvements at a lower cost than would normally be available against the diminishing returns curve of component upgrades. Often called “fully balanced” designs (fig.3), this type of amplifier has completely separate and matching electronics circuits for all four (left normal and inverted, and right normal and inverted) audio signal paths. The advantage of this design is that there are two power amps driving each coil; each amp effectively drives half the coil, with a virtual ground or zero voltage point halfway into the coil. Since each amp is only driving half the load, a significant improvement in control can be achieved, and because the voltages are in opposition, an effective doubling of slew rate (volts per second the amp can swing) is realized compared to the normal slew rate of either amp by itself. In other words, by doubling the amount of electronics circuits, a two-fold performance increase in some critical areas can be achieved with only a 50%-70% increase in cost. Normally, a doubling of measured performance would easily cost much more to achieve.

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gorion (18.04.2011)