True balanced?

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For many years audio equipment gave only token acceptance to balance outs and ins. Treated more as a courtesy or 'sure, we have them too' attitude, designers quickly hustled out recycled products with balanced outs to differentiate themselves without regard to their actual benefit. I think that happens less today but it certainly isn't gone. Before balanced circuitry became more popular than it is today the norm was to simply graft on an output inverter to an existing unbalanced design and call it balanced. Indeed, these products produced the requisite in phase/ out of phase signals needed to supply a balanced cable. Worse still, a number of designers also shoehorned inputs that accepted balanced signals but took little advantage of their common mode rejection potential. This practice was more prevalent than you might think, and still happens today. I can't tell you the number of 'balanced' audio circuits I've looked at that tacked on a courtesy inverted output signal to a single ended amplifier circuit. In fact, I would go so far as to suggest it was the norm, while a true balanced circuit was the exception. What does this added inverter look like? In most cases it was nothing more than a $0.25 op amp configured to feed off the amplifier's output and invert the signal. It requires a few resistors and an op amp. Inverted While this certainly qualifies as a balanced output it does not qualify as a balanced circuit. It is mostly just grafted onto an existing unbalanced circuit. Tomorrow let's look at what the real deal looks like.
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Paul McGowan

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