[Gumby]

I read that some preamps are not fully balanced end-to-end but have xlr inputs.    Are Bryston XLR inputs/outputs fully balanced?   What are the differences and benefits of balanced inputs which are or not true balanced design?   What’s the point of having balanced inputs if they are not?

Confused.

[James Tanner]

I read that some preamps are not fully balanced end-to-end but have xlr inputs.    Are Bryston XLR inputs/outputs fully balanced?   What are the differences and benefits of balanced inputs which are or not true balanced design?   What’s the point of having balanced inputs if they are not?

Confused.

Hi

Bryston XLR inputs and outputs are a fully 'discrete' (no transformers or IC chips) differential balanced design.  The important point about differential design is it eliminates any noise pick-up on the cables.

james

[RDavidson]

XLR's on non- balanced designs are there for hookup flexibility/options only. Yeah, a long time ago I used to think that XLR's = balanced. That is definitely not the case. Thanks to AC I know better.

More technical folks will likely chime in here, but balanced designs offer better noise cancellation / rejection. That's the primary benefit. But there's no free lunch here. Balanced designs are usually a lot more complex, in terms of circuitry. Sometimes this added complexity (and cost) is not worthwhile for the application at hand. For studio or stage use with a lot of electronics and really long cable runs, sure. Home use? Maybe...maybe not. Try it and see.

[Speedskater]

There is a great difference between an external balanced interconnect system and an internal balanced circuit. A balanced external interconnect system is always a good thing has it reduces the hum, noise & interference possibilities. An internal balanced circuit would be a possible engineering decision.

[RDavidson]

There is a great difference between an external balanced interconnect system and an internal balanced circuit. A balanced external interconnect system is always a good thing has it reduces the hum, noise & interference possibilities. An internal balanced circuit would be a possible engineering decision.

The way I understand it, balanced IC's won't really provide the benefits you list if they're not connected to a balanced system.

[James Tanner]

Hi Folks,

Here is something I wrote years ago that you may find helpful:

Is Your System Out Of Balance?

One question which keeps coming up over and over is the controversy regarding audio components being "fully balanced" versus what is sometimes referred to as "balanced converting to single ended" at the input of the electronic component (preamp, electronic crossover, amplifier etc).

The correct term for this balanced converting to single ended is more accurately referred to as "differential amplifier balancing" Popular mythology has seen fit to 'bless' the concept of 'fully-balanced' (meaning of course, two completely separate signal paths through a component, with its attendant doubling of parts cost and complexity, and halving of reliability). This approach completely misses the place, which is, of course. to eliminate hum and noise picked up by the audio cables feeding the component.

The reason for this is that a differential amplifier rejects any common-mode noise which appears at its input, by a factor equal to its common-mode rejection ratio, (normally over 1000:1). A 'fully-balanced' circuit has a common-mode rejection ratio of precisely zero, since all signal, common-mode or not, is simply amplified and passed along via the two signal paths. It then remains up to the following component to attempt to reject that amplified noise, if it has a differential amplifier.

Thus, fully-balanced circuitry is subject to passing along any noise which might be picked up on all the cables. Then it hits the final component in the system, usually the power amp, where the differential amplifier at its input is left to deal with the sum total of the common mode noise in the signal path, (multiplied by all the gain in the system). I don't think this is an ideal scenario. If each component, (source, preamp, electronic crossover, power amp), had its own differential amplifier input, it would cancel any common-mode noise which appeared ahead of it, rather than amplifying it.

[timind]

Perfect explanation James. Thanks.

[Speedskater]

The way I understand it, balanced IC's won't really provide the benefits you list if they're not connected to a balanced system.

Yes, it's the complete balanced interconnect system:

Output stage >> cable >> input stage

Not just the cable.

[CanadianMaestro]

After reading JT's explanation of differential vs balanced circuitry, I am left with the following conclusions/questions:

1. For max benefits, use balanced (XLR) cables + amp with differential circuitry. Right?

2. XLR cables + amp with "fully balanced" circuitry (not differential): no good?

3. Why do mfrs build amps with "fully balanced" (not differential) circuitry?

cheers

[RDavidson]

There are different ways to have balanced electronics. The two that I know of are dual differential (or just differential) circuitry, as most manufacturers including Bryston employ, and the use of output transformers (autoformers?). The latter can have all single ended circuitry up to the output transformer which converts to a balanced output. McIntosh does this in some of their gear I believe.

I guess there's another way to derive a balanced circuit that uses op-amps, but I don't know much about it. Might be used in some pro gear?

Note that a differential circuit basically doubles all of a component's internal parts. That's one big reason you don't see lower priced gear, especially amps, with this kind of balanced circuitry. It's expensive. Secondly, a designer may not feel balanced circuitry is needed for the intended purpose. As Bryston serves both the home audio and pro crowd, it makes sense that they produce gear that covers both bases.

[maxima95]

RDavidson

My understanding is the same.  Yet, when I read Mr. Tanner's post, which states, in part:

" ... The correct term for this balanced converting to single ended is more accurately referred to as "differential amplifier balancing" Popular mythology has seen fit to 'bless' the concept of 'fully-balanced' (meaning of course, two completely separate signal paths through a component, with its attendant doubling of parts cost and complexity, and halving of reliability). This approach completely misses the place, which is, of course. to eliminate hum and noise picked up by the audio cables feeding the component.

The reason for this is that a differential amplifier rejects any common-mode noise which appears at its input, by a factor equal to its common-mode rejection ratio, (normally over 1000:1). A 'fully-balanced' circuit has a common-mode rejection ratio of precisely zero, since all signal, common-mode or not, is simply amplified and passed along via the two signal paths. It then remains up to the following component to attempt to reject that amplified noise, if it has a differential amplifier.

Thus, fully-balanced circuitry is subject to passing along any noise which might be picked up on all the cables. Then it hits the final component in the system, usually the power amp, where the differential amplifier at its input is left to deal with the sum total of the common mode noise in the signal path, (multiplied by all the gain in the system). I don't think this is an ideal scenario. If each component, (source, preamp, electronic crossover, power amp), had its own differential amplifier input, it would cancel any common-mode noise which appeared ahead of it, rather than amplifying it. "

I have the same questions/observations as Canadian Maestro.

[RDavidson]

What I believe James is saying (and Speedskater also mentioned) is that a system has to be balanced from input to output from source to amp in order to get the noise rejection/cancellation benefits of it. Yes, that is true with my understanding. You can't have some components hooked up single ended while others are balanced. There's no partial benefit. It's all or nothing.

[James Tanner]

Hi Folks

I think maybe Maestro is asking why do some manufacturers offer a balanced signal path within the 'internal circuitry' of a component as well.

I think maybe it has a lot to do with marketing rather than a performance benefit and I believe some think that keeping the left and right channels totally separate though the internal circuitry provides for better performance. That's not Bryston's opinion of course as outlined in the above but to each his own.

james

[CanadianMaestro]

Thanks.

So....has anyone compared SQ on a reference quality track with

XLR cables throughout  + an amp with differential circuitry
versus
XLR cables throughout + an amp with "fully balanced" (separated L/R channels) circuitry?

I think that would be an acid test of the virtues of either type of circuitry.

cheers

[RDavidson]

Ideally there wouldn't be a difference in sound quality...unless your system and environment is full of noise and interference that the balanced system is rejecting. So...what I'm getting at is that one can't really say balanced is better than single ended as a blanket statement. In fact, some would argue that the lower amount of complexities in a single ended system can be better for sound quality. Like anything it's YMMV.

[James Tanner]

HI Folks,

Here's some more info on Balanced circuits I did a while back as well.

The Balancing Act

The technology of balanced-line audio wiring is quite trendy today, and there is quite a bit of information (and misinformation) in the popular press about it. For the most part, the authors are treating it as a "discovery" of some kind, and postulating all kinds of fanciful reasons as to why it is the new, the one, the only way to go. Fortunately, balanced-line technology is one of those happy circumstances, like chicken soup, which "couldn’t hurt", and sometimes can help. Since Bryston has been producing audio products which use balanced-line technology for over 20 years; we have a great deal of experience with this type of system, and have acquired an excellent understanding of the potential benefits and costs which result from it.

In general, the benefits involve a reduction in system noise. Note that I did not say a reduction in component noise. In fact, the electrical noise floor measured in each individual component, such as an amp or preamp, will at best remain the same, and may increase a bit due to the extra circuitry involved in balancing the signal, (producing a push-pull output, or accepting a pushpull, 3-wire input). The system noise can be helped, however, if you in-clude everything as installed, since on occasion a normal, 2-wire audio feed can pick up extra noise on the cable, due to the interference from power lines, RF , light dimmer buzz, or ground loops in the system. A balanced line will reject the extra induced noise by subtractive cancellation between the "plus" and "minus" sides of the signal lead, thus preventing an increase in system noise. This can be a benefit in some systems, especially when the amplifier is located at a substantial distance from the preamp. However, if the system is already well-behaved in this respect, as it should be with proper installation techniques, balanced lines will not change anything.

Other benefits have been claimed, such as an "increase in slew rate", and a "reduction in amplitude related distortions". In fact, the electrical noise floor measured in each individual component, such as an amp or preamp, will at best remain the same, and may increase a bit due to the extra circuitry involved in balancing the signal, (producing a push-pull output, or accepting a pushpull, 3-wire input). The system noise can be helped, however, if you include everything as installed, since on occasion a normal, 2-wire audio feed can pick up extra noise on the cable, due to the interference from power lines, RF , light dimmer buzz, or ground loops in the system. A balanced line will reject the extra induced noise by subtractive cancellation between the "plus" and "minus" sides of the signal lead, thus preventing an increase in system noise. This can be a benefit in some systems, especially when the amplifier is located at a substantial distance from the preamp. However, if the system is already well-behaved in this respect, as it should be with proper installation techniques, balanced lines will not change anything.

For the most part, these claims are specious. The limiting slew rate in an overall system, in terms of capability, is invariably the amplifier, unless the preamp is of exceedingly poor design. The only slew-rate which can theoretically be increased by balanced-line technology is the preamps (due to the double-ended output additively doubling the base volts per microsecond). This obviously does nothing for the amplifier. The postulated improvement in amplitude related distortions is equally unlikely. In a properly designed preamplifier, distortion is essentially invariant with amplitude, and it is more possible that the increased circuit complexity would have a small detrimental effect on the overall distortion, though in most cases this would be essentially negligible.

The claims that balanced-line technology could have some mysterious beneficial effect on the already illusory magical cable properties which are expounded upon at length by their manufacturers are so fatuous as to not justify a reply. Suffice it to say that the laws of physics still apply, whether the line is balanced, unbalanced or tied around your grandmother's left leg. Balanced-lines do not enjoy any magical properties. They do have some potential advantages for some systems which could justify the moderate extra cost
and complexity involved in their implementation, the disadvantages are inherently rather minor, and can be considered innocuous enough to ignore where the system cannot be brought under control though standard practices in installation.

Indeed, Bryston provides all of our amplifiers, most preamplifiers and our electronic crossovers (optional) with balanced-line technology as standard, since in complex sound systems, the chance for noise and interference is much higher.

IN CONCLUSION: balanced-line technology:

Will:
1. Reduce any system noise caused by ground loops, RF, power lines etc.
2. Allow shorter speaker leads by permitting the amplifier to be placed adjacent to speakers without extra noise.

Will Not:
1. Increase the slew rate of an audio system.
2. Affect the given cable properties.
3. Improve distortion characteristics in an otherwise well designed audio product.
4. Improve on the individual audio component noise.

[CanadianMaestro]

^ good stuff, thanks.

Quoting JT:

IN CONCLUSION: balanced-line technology:

Will:
1. Reduce any system noise caused by ground loops, RF, power lines etc.
2. Allow shorter speaker leads by permitting the amplifier to be placed adjacent to speakers without extra noise.


This I agree with. In my own system, going balanced made an improvement. I suspect I have power line noise, as I do not have a dedicated room, and my power amp is next to my spkrs. But all considered, I enjoy my system very much.

[Gumby]

James thanks so much.  The articles have brought me clarity regarding this whole balancing act. 

I can see now why a sound crew at a rock concert would want to implement a balanced system. 

I guess the only way to tell if a balanced setup would benefit the system at home is to demo it.  I don’t know if there is noise in the AC line.   

This leads me to the BIT 15.   Would a system with noise be better served with a power conditioner or a balanced setup?   

[James Tanner]

James thanks so much.  The articles have brought me clarity regarding this whole balancing act. 

I can see now why a sound crew at a rock concert would want to implement a balanced system. 

I guess the only way to tell if a balanced setup would benefit the system at home is to demo it.  I don’t know if there is noise in the AC line.   

This leads me to the BIT 15.   Would a system with noise be better served with a power conditioner or a balanced setup?

Hi

I think because the world is full of RF these days and getting worse all the time I would use balanced lines where-ever and when-ever you can. 

Cables are antennas and eliminating them from become a noise potential is critical in my opinion as it leads to a system where micro details are finally able to be resolved.   Noise of all kinds is insidious which continually rides on the signal and you really do not notice it till it's gone.

james