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Single ended vs xlr balanced

I have switched backwards and forwards (going slightly mad in the process) testing (long run) interconnects.
I know some sound engineers, and they tell me I am probably persuading myself that balanced is better than single ended and THERE IS NO REASON WHY SINGLE ENDED CAN SOUND INFERIOR TO BALANCED. Sorry to use capitals but this seem to be a fair summary of the be all and end all of technical discussion. If I was to guess however, my mind would tend to follow the technical opinion not go against it, surely? In my mind the balanced is a deeper more airy sound, just better presence all round. The technical response is that I am not comparing like with like, as the balanced runs at higher voltages and subsequently higher volume (6db). I had a shock at this news and found out therefore by accident that my Bryston 28bsst2s amps have a switch upping the output from 23 to 29db to compensate. Also did I hear properly that Bryston kit is set up preferring balanced? My processor is a Bryston sp3 so maybe my preferred balanced system  is what I needed anyway. But it is odd that a reputable company like Bryston would have such a policy (if it has foundation) and not stress that on their literature. If my system can be adjusted for speaker levels then volume output is irrelevant - or is it if that higher voltage has some effect?
And don't get me started on aes/ebu vs spdif! The aes to me is noticeably superior for the same reasons as the rca vs xlr debate. Then hdmi vs spdif ... (Time for my medicine ........)
So my question is - forgetting technicalities which can get more and more complicated by the minute  - do other peoples' ears agree with mine?
tatyana69
almarg's avatar
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almarg
9,670 posts
 
Excellent input from Mward. There are certainly many preamps that would not be able to drive 12K with good results, especially many tube preamps, but would be very happy driving 100K (which BTW probably means that 50K is applied to each of the two signals in the balanced signal pair).

In addition, it can be inferred from the fact that the balanced input impedance of the amp is much different than twice its unbalanced input impedance that there are considerable differences in the designs of the balanced and unbalanced input stages. (In contrast, for example, to many amp designs in which the same input stage is used for both balanced and unbalanced inputs, with one of the two input signal lines simply being grounded via a switch or an external jumper when the stage is operated with an unbalanced input signal). So even if the preamp could drive 12K without issue, it is possible that the balanced input stage of the amp simply sounds better than the unbalanced input stage. Even though the amp is not "fully balanced."

Regards,
-- Al

erik_squires
16,378 posts
 
@mward

The input buffers might be making all the difference there. Depends.

@almarg is right, impedance differences on the input are good indicators of the circuit paths not being the same.

I’ve seen some amps whose only claimed to balanced inputs was the XLR plug, but otherwise was completely single ended. However, most pro gear is at least truly balanced inputs, but single internally. That is, they use mirror imaged op amps or a transformer on the input to convert. That can make a lot of difference. The Op Amps can sound better because they work in opposition and cancel errors, the transformer in adding some warmth, and in both cases common-mode noise is greatly reduced, not to mention the ground loop issues previously discussed.

There is also some anecdotal evidence that merely raising the impedance of a input circuit sounds better. Whether it's universally true, or only sounds better for less robust designs is unknown. The math says the differences should be infinitesimally small with most well designed gear.

Sadly the Parasound A23’s I owned were of the former, I believe, and just had convenience plugs. I was unable to tell the difference in using either one. My current amps are XLR only , and truly balanced inputs, so I have no way to compare.

Best,

Erik
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kijanki
4,432 posts
 
XLR might be better where ambient electrical noise is high, but requires additional circuitry that may reduce transparency.  Terms "Fully balanced" and "Truly balanced" mean something different.  True balancing is achieved by means of the input transformer or instrumentation amp, while Full balancing is achieved by dedicating one amp for each leg of the signal with the speaker connected between outputs.  These amps should not be independent, because even slight difference in gains would greatly reduce common mode noise rejection. Fully balanced amp does not produce even harmonics while still outputting odd harmonics.  I use very short (0.5m) balanced cable.  Short, because negative effects of the cable will increase with its length, as Al stated, and balanced because my class D power amp has only balanced input (mature decision).   My small Rowland 102 utilizes THAT1200 instrumentation amp.  Link below.  Gain setting resistors in such amp reside on the same substrate and are laser trimmed to match -  for stated 90dB rejection, they are matched to 0.0015%.  B&O module inside has already balanced input, as eric_squires mentioned, but input imepedance is only 10k.  External amp increases impedance to 48k also providing (most likely) better common mode rejection.  Transformers are also a good choice but they slightly distort at low frequencies (may not be audible).

http://www.thatcorp.com/datashts/THAT_1200-Series_Datasheet.pdf

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almarg
9,670 posts
 
Good comments by Erik and Kijanki, as usual.

A clarification to comments a couple of people have made, to the effect that a fully balanced amp requires essentially two separate amps on one chassis, one amp for each polarity of the balanced signal pair. The implication being that twice as many parts are necessary than would be required for a comparable single-ended signal path.

That is one approach to implementation of a fully balanced amp. But another approach, which I suspect is used more frequently, is to use a differential stage, having differential inputs and differential outputs, for each of the active stages in the signal path.

See the section on "differential amplifiers" in this paper at Ralph’s Atma-Sphere site for a simplified schematic representation of a tube-based differential stage, and also for a summary of the advantages and disadvantages of that approach. Note this statement in the disadvantages section:
Differential amplification takes more parts to execute. For a given number of stages of gain, differential amplifiers have about 50% more parts.
Regards,
-- Al

mesch
3,527 posts
 
Though it seems that the answer in the 1st post provided by aka_ca proves correct, I truly enjoyed the education I received via followup. Thanks!
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