Hi-Rez Highway

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RE: Balanced versus unbalanced analog connections

Posted by Charles Hansen on June 2, 2017 at 19:14:02:
Oppo claims the outputs on its player sound identical, yet a reviewer found "major sonic differences...noticeable immediately". So what's up with that?

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In my experience, most (even those who should know better) don't control all the variables properly when conducting comparisons such as this. I've seen experienced reviewers writing for print magazines attempt to reach conclusions while using different brands and models of cables for each connection. And even if there is a difference, is it due to the source or the receiver?

It's a difficult experiment to control, and may not even be possible with some equipment. An example of this was Sony's original SACD player, the SCD-1. It was pretty much universally agreed that the single-ended outputs sounded better than the balanced outputs. When you look at the circuit, this makes perfect sense. At some point after the DAC chip, the signal was purely single ended. The RCA jacks connected directly to this point, but the positive (+) and negative pin (-) of the XLR went through two op-amp buffers with 100% negative feedback (to create unity gain), one wired in non-inverting mode and the other in inverting mode (to create the out-of-phase signal). It's no surprise that when connecting that output signal to a true differential balanced input on a preamplifier that the result would be a reduction in sound quality, as signal was passing through an additional amplification stage of lower performance than the discrete unbalanced circuitry used for the single-ended output.

The reason for audiophiles to use balanced has almost nothing to do with the reason balanced connections are mandatory in professional recording studios. In the pro environment they are worried about picking up external magnetic hum fields in long (100') cables carrying low-level (microphone) signals. That is not a problem at all for home playback - I've even used 20' unbalanced cables between a low-level MC phono cartridge and the preamp without hum problems.

The real sonic advantage of balanced only comes into play if the internal circuitry is truly differential from input to output. Since every circuit in the world (analog or digital, tube or solid-state, audio or video) is nothing more than a modulated power supply, it only makes sense that the quality of the power supply is important. And as there is no such thing as a "perfect" power supply, gains can be made by reducing the audio circuit's sensitivity to imperfections in the power supply. A differential balanced stage will typically exhibit an increase in power-supply rejection ratio (PSRR) between 40dB (100x) and 80dB (10,000x) over identical single-ended circuitry. Therefore using balanced differential circuitry is like making the power supply between 100x and 10,000x better.

The easiest way to hear what difference this makes is to listen to a Pono Player using a headphone with detachable cables. When comparing otherwise identical single-ended and balanced harnesses (same cable manufacturer and model), the signal path from the DAC chip to the headphone driver is fully balanced differential all the way through for a balanced harness, while a single-ended harness is fully balanced differential *except* for the final output buffer stage. The only variable in this test is whether a single stage in the chain is operated in single-ended or differential balanced mode. There are many reports on the internet about the improvement in sound quality available from using a balanced connection, but I've never seen the opposite conclusion.

The bottom line is that properly executed differential balanced circuitry will always sound better - but only if all else is held equal. The penalty is pretty much a doubling of the circuitry and parts count - hence price, size, and power consumption. There are other ways to both improve power supplies and also reduce a circuit's sensitivity to imperfections in the power supply, but those can also be applied to differential balanced circuits for further improved performance. In other words, it is also possible to make a single-ended circuit perform better than a balanced circuit - but only by improving the single-ended circuit and not the balanced one. That is why the caveat "if all else is equal" is so critical.

As usual, strictly my personal opinion and not necessarily that of my employer or hairdresser.