Join Date: Nov 2007
Location: Gaithersburg, MD
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Although I think this subject has been adequately covered, and the answer seems to be that balanced audio is not worth it. I thought this brief anecdote might be interesting.
A number of years ago, a small manufacturer of audio gear, Frank Van Alstine, built a completely balanced audio system. It required a four-channel DAC and audio circuit set, a four-channel preamp, and a four-channel power amp (or two stereo power amps) maintaining balanced operation from input to output, summing the signal at the speakers. In theory, this canceled all common mode distortion in the system, and could provide audibly superior musical operation, depending upon how much distortion was originally there to cancel. Of course it also essentially doubled the cost of the audio system.
Although this was an experiment, it had positive results. It produced an additional 3 dB in dynamic range. The audible improvement in this fully balanced system alerted him that there must be distortion from components in the audio chain that he hadn’t addressed.
This sent him on a serious effort to discover remaining weak links in the audio gear he produces and fix them at a reasonable cost, if possible. When these improved components were tried again in a fully balanced system, they resulted in only minimal improvements. The whole exercise was helpful in identifying where potential improvements might produce audible results.
An interesting question comes out of all this. Why are there never balanced interconnects coming from a phonograph? Phono cartridges put out the lowest voltage signal found in home audio, about 5 mV for a moving magnet cartridge, and they are the most prone to interference. If they don't require balanced connections, why do some people want to pay extra for balanced connections between a preamp and amp where much higher signal voltages are involved? Was it never done years ago because no one thought balanced connections were needed in home audio, or is there something inherent in these pickups that prevent using that design?