Balanced connection for domestic audio: does it make sense?

[jasonhanjk]

It's fun watching discussion that have no ending.

Instead of focusing building an amp around 5532 using differential config and non-inverting.
The topic now sway towards equipment that are not design properly causing unbalance to be worse than balance.

 

[pma]

Well, that may be true but this thread is about domestic audio.

I know you really like these old machines, but the world has moved on since the early 80s.

Exactly. 600 ohm has never been any standard in domestic audio and is no longer used in newer pro audio. And transformers degrade the audio band signal especially if there is a SINAD measure of 120dB so widely used now (though questionable). They also make no isolation for RFI signals due to stray capacitance. Enough measurements and experience here on this.

 

[pma]

Instead of focusing building an amp around 5532 using differential config

This is a routine design, nothing to investigate. The debate is as it is because of so wide range of poster's knowledge and experience. It is an internet and this is a popular forum. It is not any scientific or engineering forum by far. It is however impossible in an internet open platform. Internet is great and horrible at the same time.

 

[KSTR]

It's fun watching discussion that have no ending.

Instead of focusing building an amp around 5532 using differential config and non-inverting.
The topic now sway towards equipment that are not design properly causing unbalance to be worse than balance.

"No Ending" just means we have a profound circle of confusion here ;-)

Using unbalanced may or may not create hum/buzz problem in the real world, sorted by importance (IME):

• When conncting gear that both has audio GND connected to mains earth, either directly (worst case) or the "GND isolator" circuit often seen, a resistor shunted with a small capacitor shunted with anti-series diodes (which must withstand the rated short-circuit current for the circuit breaker / fuse in you house's distribution panel). The larger the GND difference the bigger the issue, either from using different outlets or from I*R drop along the PE conductor that carries mains filter deflection current. "Antenna" feeds for cable TV etc also establish such a polluted GND scenario.
• When one of the components is earth-grounded is connected to a class-II (2-prong) "isolated/floating" device whose supply has significant mains coupling. SMPS are most offending as the couple the recitified mains, whereas 50/60 transformers couple the "pure" mains only (50/60Hz + some harmonics + noise)
• When both devices are class-II "isolated", the system GND being fully "floating," and have medium to high coupling to the mains, again SMPS being most problematic. The worst case -- in the US -- would be to connect one device on one phase of 110-0-110 biphase net, the other on the other. Leakage doubled. In 3-phase networks, using differernt phases.

The problem simply scales with the shield resistance of the unbalanced cable, the higher this resistance and the longer the cable the more error voltage is developped. The bottom level is set by the internal routing of audio GND in the device itself and some devices have, as noted, issues here and some even generate their own noise from internal currents sharing a GND path between inptus/output connectors.

As for the solution without modding the devices and trying to establish a system-wide common signal ground grid/plane (which is a lot of effort), the simple 4-resistor subtractor recevier is good enough to reduce the error signal to be insignificant in most cases. 20...30dB reduction is a lot here.

For precision/measurement applications, you will want something better, depending on the needs:
- transformer for best LF CMRR and more importantly, to avoid CM clipping. RF must be taken care of seperately.
- balanced CM- and RF-bootstrapped high-Z instrumentation input, Whitlock style. Pin 1 connected via direct RF path to chassis and with a series R for the DC/LF path, to avoid large balancing current for above case 1.
- use excellent cabling especially when the cable is expected to carry shield current.

 

[JSmith]

It's probably best to never assume though when buying gear;

https://www.audiosciencereview.com/...-review-av-processor.20155/page-8#post-665119

But when I measure dynamic range, RCA out is better and actually matches their spec!

You buy a high-end processor to get balanced output and seemingly its unbalanced output is lower noise.

This is why measurements in general and in turn this site are important before committing to a purchase.



JSmith

 

[Gadget Goober]

For me, it's the ability to listen with my higher impedance cans at a more enjoyable volume on my portable devices, mostly... nothing more or less. The possibility of up to twice the voltage slew rate and 4x power is the main driving force, even on my Schiit Magnius. The runs are short, so I'm not concerned about sound quality and I don't believe I can tell a difference between SE and Bal in this application. The single ended output still just won't cut it for my K240DF's, I need the added "umph"

 

[charleski]

I suppose one thing has to be pointed out so that people are absolutely clear. In a professional environment there are a huge number of reasons why you should use balanced connections by default, not least of which is the noise rejection factor brought up by @DonH56. In terms of the performance metrics we prize, a lot of professional gear is merely "good enough" rather than "state-of-the-art", but the critical aspect is that it's reliable and resilient. You need your gear to work properly even though you're tearing down the stack and rebuilding it in a different venue several times a week, and you need it to work now, when you've got a crowd of drunk fans who've already waited an hour for you to come on stage.

But these considerations simply don't apply to the vast majority of domestic systems, and there's no point solving problems you don't have. I'm not a professional engineer, but I was always told the first rule of engineering is, "If it ain't broke, don't fix it."