Balanced connection for domestic audio: does it make sense?

[jasonhanjk]

Lower distortion? There’s a blog post from Benchmark that states the opposite is the case for headphone outputs, as you have twice the number of amplifiers driving half the impedance. They still recommend balanced for line-level, but their claim of “substantial performance improvements” is somewhat vague and frustrating.

Balanced connections certainly promise better SNR, but what length of cable do you need for this to become significant? Sure, problems with the mains wiring can cause ground loops in some installations, but in the absence of a specific problem like that, how much would the SNR improve over a single-ended connection?

The one circumstance I can think of in which it would make sense to use balanced by default would be running long cables from a DAC to powered speakers through ducts that also contain power and network cabling. But then most active speakers only have balanced inputs anyway.

Unbalance are better if your cable from the DAC to amp is very short.
Look at OPA1678 datasheet, non-inverting have superior THD+N than inverting configuration.

Good book to read [Small Signal Audio Design]

 

[Veri]

Unbalance are better if your cable from the DAC to amp is very short.
Look at OPA1678 datasheet, non-inverting have superior THD+N than inverting configuration.

Good book to read [Small Signal Audio Design]
View attachment 116295

Well yeah if noise in SE circuit will be n, identical dual mono set-up will be 2n. If n is low enough that still shouldn't have to be a problem, though.

 

[KSTR]

Balanced inputs are what's important. Balanced output are not required or extraordinarily simple to create: just mirror the output impedance of the hot leg on the ground. Balanced connection means impedance-balanced connection, not voltage-balanced connection. The actual voltages don't matter, only the difference -- the core of the working principle, the subtraction of the voltages and the referencing of the difference to the local ground.
Don't ever let the shield current be part of signal current.

Unbalanced was never developped for connecting gear, it was designed for connection within the same unit where the circuit ground potential is guaranteed to be the same.

The noise penalty in balanced receivers can be mitigated by circuit design

 

[Mnyb]

I never got the idea of balanced headphones really . Here i think benchmark are 100% correct . there is only one coil in each driver we don't have balanced passive speakers either for obvious reasons even if the amp can be bridged coupled (which is kinda balanced ).

But some headphone amp has their best performance in balanced mode and you have to get that special cable ? but it's kinda of a solution searching for a problem .

For active speakers i would very much like balanced xlr here we start to have lengths even at home and possible tangled together with power .

Wonder why audio never uses balanced/differential current loops like industrial sensors do ?

 

[jasonhanjk]

Well yeah if noise in SE circuit will be n, identical dual mono set-up will be 2n. If n is low enough that still shouldn't have to be a problem, though.

Dual mono for speaker amp?
Playing 2 identical mono speakers will reduce noise by 3dB.

 

[KSTR]

Wonder why audio never uses balanced/differential current loops like industrial sensors do ?

Some companies have done so (unbalanced current loops at least). Designing a low-noise precision differential current source is not that easy and has the same stability issues that voltage drive (albeit inductance is the offender here). I don't think it has any benefits.

 

[Mnyb]

Some companies have done so (unbalanced current loops at least). Designing a low-noise precision differential current source is not that easy and has the same stability issues that voltage drive (albeit inductance is the offender here). I don't think it has any benefits.

maybe you don't have 200 meter long cables in audio and absolute level might not be important . You mitigate the voltage dropp with a current loop .
You get predicable signal levels . And the inputs of industrial current loops are often low impedance 100-500 ohm ? it may impact noise pickup if the whole loop is low impedance ? But here ends my hands on competence with the actual circuit design I just use these kind of things and noted that voltage signals in heavy industry are nosier and have losses in practice . And the actual resolution is anyway far lower than audio so some obvious cons you mentioned might not even be an issue.

 

[KSTR]

Signal voltage drop is a non-issue.
The one and only problem with unbalanced connections that the voltage drop on the signal "return" path (the cable shield) is part of the signal as seen by the receiver and the receiver cannot discern between signal and R*I noise when some stray I is flowing on the shield...

 

[Mnyb]

Signal voltage drop is a non-issue.
..

yes in audio i agree you just adjust the gain everything is relative and the losses in audio system are very small anyway non-issue as you say fraction of dB .

 

[josh358]

Lower distortion? There’s a blog post from Benchmark that states the opposite is the case for headphone outputs, as you have twice the number of amplifiers driving half the impedance. They still recommend balanced for line-level, but their claim of “substantial performance improvements” is somewhat vague and frustrating.

Balanced connections certainly promise better SNR, but what length of cable do you need for this to become significant? Sure, problems with the mains wiring can cause ground loops in some installations, but in the absence of a specific problem like that, how much would the SNR improve over a single-ended connection?

The one circumstance I can think of in which it would make sense to use balanced by default would be running long cables from a DAC to powered speakers through ducts that also contain power and network cabling. But then most active speakers only have balanced inputs anyway.

This depends entirely on circumstances. I have bad hum here when I used balanced lines with certain equipment, even with ground lifters. I suspect it's because the cheapskate power company gives us two phases of three-phase commercial power, but whatever the cause, it doesn't affect balanced lines.

The point is that you're going to have hum in some circumstances, and if you buy unbalanced equipment, there may be no safe or economical way to eliminate it. Subtler issues aren't the problem -- the S/N ratio of something like the AHB2 may be a bit impaired if you use lower levels and/or unbalanced connectors in a good environment, but in practice, the S/N is so spectacular that you're never going to hear the difference.

 

[DonH56]

Lower distortion? There’s a blog post from Benchmark that states the opposite is the case for headphone outputs, as you have twice the number of amplifiers driving half the impedance. They still recommend balanced for line-level, but their claim of “substantial performance improvements” is somewhat vague and frustrating.

Balanced connections certainly promise better SNR, but what length of cable do you need for this to become significant? Sure, problems with the mains wiring can cause ground loops in some installations, but in the absence of a specific problem like that, how much would the SNR improve over a single-ended connection?

The one circumstance I can think of in which it would make sense to use balanced by default would be running long cables from a DAC to powered speakers through ducts that also contain power and network cabling. But then most active speakers only have balanced inputs anyway.

I have no dog in this hunt, do what you want. I did not read Benchmark's blog. I took your question as a generic ask and not applied to a specific device. But if your argument is to convince people differential/balanced circuits do not matter in the home, my experience differs.

I have a couple of short posts on the subject:
Differential circuits: https://www.audiosciencereview.com/...d-balanced-unbalanced-and-all-that-jazz.1352/
Ground loops: https://www.audiosciencereview.com/forum/index.php?threads/ground-loops-101.7162/

Yes, using differential circuits provides lower distortion, in theory and in practice, but of course it depends upon implementation. My world is at frequencies well above audio but the circuits often have to work to DC, and differential operation does what I said IME. Like Ripley, believe it or not, or review the info on the Web or engineering texts. Note there are several "flavors" of balanced circuits in audio, and not all are fully-differential, so do not all provide the same level of benefit. Twice the amplifiers is not how all differential circuits work, but for those that do, noise is not usually correlated so you get twice the signal swing but noise only increases by a factor of sqrt(2) and thus a 3 dB improvement in SNR. Distortion improves to the extent the two sides are matched; ideally even-order distortion is completely canceled (odd-order distortion is not affected).

The SNR and distortion improvement is not related to cable length except as regards to noise rejection. Ground loops are not a wiring "problem"; they are a fact of life when you have different ground paths in a system. They are pretty common in audio systems, home or pro, as evidenced by the many threads on the subject. At least in my experience they seem fairly common. So I would not discount that advantage.

As for noise rejection, many consumers bundle wires together for a "clean" look and that can lead to noise coupling. A balanced connection better rejections LF and HF noise. LF noise is usually inductively coupled by adjacent power lines. HF noise can be injected directly into the power lines or radiated and injected "over the air" from things like switching power supplies, dimmers, refrigerator and HVAC motors. In one case an aquarium pump was the culprit. The cable lengths do not need to be long, and in most but not all cases low-level inputs like phono inputs are most affected. However, I have seen plenty of cases where RFI was coupled onto line- or high-level cables and caused problems. Having balanced cables that isolate the signal path from the shield provides greater immunity to LF and HF noise sources. Again in my experience, which may not match yours, there are plenty of noise sources in the home that problematic. Aside from my systems and that of some friends (plus the 'net, of course), most of my experience in this area is from years ago when I was helping to install home and pro systems (hundreds of them) and, while I would not say the problems were really "common", nor were they at all rare in home installations. Since those years I have helped many friends deal with noise issues, and dealt with them in my own systems through the years (then and now).

It seems our background and experience is quite different on this subject. It happens.

Balanced differential is not in general the same as bridging amplifiers for greater voltage swing; bridging offers some of the benefits but generally in a lesser way, and additional drawbacks.

 

[restorer-john]

Some companies have done so (unbalanced current loops at least).

Sony introduced a range of amplifiers and even a few external components (tuners etc) in the very early 1980s which implemented what they called ACT (Audio Current Transfer). Internally, the stages were coupled with VI converteres with servos. Some amplifiers had a special "ACT" RCA connections from current drive external components.

Here's a basic description and concept:

Sony TAF-555es Integrated amplifier (1982)

Significantly improved S/N at low listening levels:

Here's the relevant VI section (across the two images) for the TAF-555es:

Here's one of the internal VI sections in the TA-AX500 integrated (1982):

 

[DonH56]

Off-topic post inspired by John, blame him...

Has anyone read this book on using current drive for speakers? I've had it in my cart for a year or more but never got around to buying it. The concept has been around "forever" though few amplifiers implemented the approach AFAIK. I had another book on the subject and went digging through my shelves a year or three ago but it must be in the black hole masquerading as our basement "storage" room.

Current-Driving of Loudspeakers: Eliminating Major Distortion and Interference Effects by the Physically Correct Operation Method, by Esa Meriläinen
https://smile.amazon.com/gp/product/1450544002/ref=ox_sc_saved_title_9?smid=ATVPDKIKX0DER&psc=1

 

[SIY]

Has anyone read this book on using current drive for speakers?

Yes. It's interesting, though the author is a bit... obsessed. At the end, I felt like I didn't get much more than I learned from the Mills and Hawksford papers. Still, I'm glad I bought it and read it. And I remain unconvinced that this is, as a practical matter, the "universally right" way to drive loudspeakers.

 

[Helicopter]

Yes. Yes it definitely makes sense, more for the ground hum elimination and voltage increase than anything else, but the noise rejection and connectors are also worth it.

Especially sensible with phono gear that is so prone to ground hum.

RCA is an inherantly flawed design. It is prone to poor connections, noise, and hums.

On systems under $1000, RCA may have a cost advantage, and we shouldn't be willing to pay obscene amounts for balanced connections though.

 

[Standingstones]

A few years back I had a ground hum problem with an amplifier I had. I tried XLR cables and that cleared up my problem. I decided to stick with XLR cables ever since.

 

[Harmonie]

I'm lucky enough to have no hum issue with my RCA cables pugged into a simple CD transport, dac, power amp, speaker system.
The only hum I get is when connecting carelessly with fingers touching the hot point and making a loop.
But once connected, I enjoy the silence.

 

[rcstevensonaz]

It also typically gives you 2x the output voltage, which can be useful.

But, that voltage bump can also become a problem when all of your other audio components are unbalanced.

In my case, most of the audio sources routing into my home audio mixer (Ashly LX-308B) are unbalanced: Squeezebox, Topping D30, Echo Input, Turntable. So, I just bring in the other sources (Topping D90) as unbalanced so that it is easier to balance volume levels across the sources.

But in my case, all interconnects are short, and all equipment is sitting on the same ground via a shared power strip (Furman M-8x2)

 

[Lambda]

we don't have balanced passive speakers

I only have balanced speakers? since all my Amps are full bridge...

Note there are several "flavors" of balanced circuits in audio, and not all are fully-differential, so do not all provide the same level of benefit. Twice the amplifiers is not how all differential circuits work, but for those that do, noise is not usually correlated so you get twice the signal swing but noise only increases by a factor of sqrt(2) and thus a 3 dB improvement in SNR. Distortion improves to the extent the two sides are matched;

I came here to say this!
Verry well said, thalks for this.

 

[KSTR]

Off-topic post inspired by John, blame him...

Has anyone read this book on using current drive for speakers? I've had it in my cart for a year or more but never got around to buying it. The concept has been around "forever" though few amplifiers implemented the approach AFAIK. I had another book on the subject and went digging through my shelves a year or three ago but it must be in the black hole masquerading as our basement "storage" room.

Current-Driving of Loudspeakers: Eliminating Major Distortion and Interference Effects by the Physically Correct Operation Method, by Esa Meriläinen
https://smile.amazon.com/gp/product/1450544002/ref=ox_sc_saved_title_9?smid=ATVPDKIKX0DER&psc=1

I've been using current-drive for a long time, more exactly, a "best-compromise" source impedance profile vs. frequency. Any drive impedance may span a range from -Re (undoing the coil DCR) to infinity and any given driver will have a profile that gives best results. For AMT tweeters it's pure current drive, for VC-type mids and woofers (especially when ported) you need some "spot" damping, also to avoid chaotic phenomena/instability. The lesser the quality of the magnetic circuit the more it helps but it can help only so much until other effects become dominant errors. At any rate, higher drive impedance, even if it's only a few ohms, reduces power compression.