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Unbalanced and Balanced Clarification

Discussion in 'Sound Science' started by exsion, Jun 10, 2017.
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  1. pinnahertz
    Yes, ground loop noise is "common mode".
    Balanced mode rejects common-mode noise, either induced our coupled from the outside environment or impressed on the line because of a difference in ground potential. The fact that your balanced input doesn't reject it indicates one of two conditions: the balanced input has a limited common-mode rejection ratio (yes, you can have a balanced input with poor CMRR, it's done all the time, and CMRR is almost never included in the specifications!), or the noise is not common-mode (unlikely).
    That would be common-mode noise.

    Good CMRR is greater than 70dB, hopefully. There are many variations on design, and many suffer from poor CMRR under certain conditions, such as an imbalance in source impedance.

    Here's a link to a good monolithic solution, a THAT 1200. It is an expensive part, and not typically used in consumer applications. Note the data about CMRR under a condition of imbalanced source resistance, and note too that CMRR is not flat across the entire audio band. This is very typical, and the THAT 1200 solves the problem mostly. Less expensive designs use a simple differential input with terrible CMRR and intolerance to impedance imbalances, or they use a conventional instrumentation amp configuration, better, but still can have issues if not properly done.

    A good balanced line receiver will have 90dB CMRR across the audio band, a bad design might hit 60dB at 60Hz, then collapse to 10dB mid-band and up.

    There are also maximum voltage limits to a devices CMRR, which is one of the advantages of using a transformer as a balanced line interface. That and complete isolation.
     
    Last edited: Jul 9, 2017
  2. TYATYA
    I conclude : A$K dap Balance mode active just when play and deactive when pause.
    When feeding bal. via Trrs to dual xlr3 (use pin 2 and 3 of each, no ground) to amp, if touch any thing incl the charge metal wire on any pin of trrs or xlr, nothing happen. Do the same but stop, big noise will be heard.
    Why a quite big nois signal dont transfer to the amp w/o grounded? I do believe that is effective of balance.

    When stop the dap, balance mode no active( to save battery or somehow). Touch a hand or any thing can see phenomenon
     
  3. pinnahertz
    OK.

    I do not conclude the same thing. But then I really can't troubleshoot anything this way.
     
  4. Sujay Rao
    I have a question. I have an Onkyo DP-X1 which I use a lot. It has a balanced 2.5 mm TRRS out. If I should want to use a portable balanced amp to run a modded balanced high impedance Beyerdynamic, doesn't it make sense for the amp to have a balanced input. What is the point in boosting signal from a balanced output capable high-end DAP if one has to feed it into an unbalanced input in the balanced amplifier? Is there a way for the separation of each balanced channel to be maintained from the DAP all the way through to a a pair of balanced cans?
    Is there such a thing as a balanced portable amp with balanced input?
     
  5. pinnahertz
    Not necessarily. In a headphone amp a balanced input and balanced output sever two entirely different purposes that are mutually exclusive.
    Not much. But then running short balanced interconnects within a home system doesn't make much sense to begin with.
    Yes, but there is really nothing to be gained.
    Doubtful, but I'll leave it to others.
     
  6. Speedskater
    When I asked about a TRRS being a balanced connector, I was thinking that the 'S' Sleeve was acting as a shield for a balanced interconnect system. But of course a headphone cable doesn't need a shield. And neither do some of the Cat5 balanced interconnect cables.
    * * * * * * * * * * * * * * * *
    Is there such a thing as a balanced portable amp with balanced input?
    I don't know if there are, but unbalanced interconnects are a thing of the past and there's good reasons for having balanced inputs.
     
  7. pinnahertz
    ...and for stereo a pair of balanced lines requires 4 conductors.
    * * * * * * * * * * * * * * * *
    Well, back in reality on earth, the vast majority...and I mean VAST...is unbalanced only, today, now, currently. And that's not likely to change...ever. There's simply no need to balance in most cases. The "thing of the past" would be balanced interface which predates consumer audio by st least a couple-three of decades.
     
  8. thedesigner2011
    Say I have a DAC that has balanced outputs that I use to connect to the balanced inputs of a headphone amp, then out to a headphone with a balanced cable. What is the difference there as opposed to the same DAC with RCA outputs to the RCA inputs of that same headphone amp, which I then send out to a headphone with a balanced cable?
     
  9. pinnahertz
    Apparently a few things need to be understood first.

    1. There is one purpose, and one purpose only, of a balanced interconnect between two devices: noise immunity. Specifically noise occurring equally and in phase (common mode) on both signal wires, which is termed Common-mode noise. Common mode noise can come from several sources, but the important part is that it's common to both signal wires.

    2. To accomplish this noise immunity takes additional circuitry and components resulting in a more complex, and expensive interface with more opportunities for noise and distortion. Circuit noise is not common mode noise, so it is not cancelled. More devices result in slightly higher noise. Achieving high Common Mode Rejection Ratio is difficult with discrete components, and circuits would require custom trimming to maximize CMRR, thus the effective way to do it is to us integrated/monolithic solutions with extremely high precision trimmed internal parts. Passive balanced interfaces use transformers which while excellent in some cases do produce some distortion at very least, and lots of it along with poor transient response in the worst cases. Balancing is not a free ride!

    3. The necessity for all this noise immunity is prevalent in pro audio systems where long cable runs of many meters are common, and interconnecting rooms or entire facilities is required. The necessity for additional noise immunity in home systems with 1 meter or so interconnects is virtually nonexistent.

    4. The use of balanced headphone amp outputs driving headphones wired for balanced drive has the advantage of gaining 6dB of additional voltage swing over a single-ended system using the same power supply voltage. That last bit is key because designers are not necessarily limited by power supply voltage alone. It's possible, and easy, to design and single-ended amp with as much or more voltage swing as a differential output amp (a loose definition of "balanced") simply by properly designing the power supply. There is a point to wiring headphones with two separate wire pairs all the way to the drivers, but a common ground can be shared at the connector with no ill effects, and that makes the headphones unbalanced.

    So to your question, "What is the difference there as opposed to the same DAC with RCA outputs to the RCA inputs of that same headphone amp, which I then send out to a headphone with a balanced cable?", the answer would be: no difference other than the addition of whatever anomalies are added by the additional required circuitry.

    If you are a minimalist, purist, economist, or pragmatist, you'll leave the balanced interconnect for the applications that actually require it.
     
  10. thedesigner2011
    Thanks for the explanation
     
  11. bigshot
    I'm always amazed at how much discussion is generated in audiophile circles by things that really don't matter.
     
  12. L8MDL
    Having had the pleasure of listening to a Pono player using balanced lines to Sennheiser HD600's or HiFiMan 400s' or Meze 99 Neo's, compared to single ended, I'd say it does matter.
     
    Last edited: Jul 10, 2017
  13. bigshot
    How far away from your player are you sitting when you listen to it? A block away?
     
  14. castleofargh Contributor
    something like the pono is based on atypical design decisions, so IMO it's a mistake to use it to draw conclusions about balanced vs SE. and in any case, one device can't possibly be representative of a category, that's just very wrong. the SE vs balanced of the pono tells us about the SE vs balanced of the pono.
    also the change in loudness on Pono and many other amps makes any uncontrolled listening test mainly irrelevant because then we're not judging the sound, we're judging the subjective impact of louder sound. this has to be in the top five of mistakes most made by audiophiles.


    @bigshot, there are many instances where using the balanced output sounds very audibly different. we can't just rule out all testimonies as placebo or failure to properly volume match before testing. it's for sure a huge part of the testimonies but not all them. ^_^
    fairly often we end up with double the impedance using balanced output. that alone can make audible changes in many circumstances.
    I agree with @pinnahertz and the logical understanding that we really don't need a balanced output for high gain, low noise, and low crosstalk in a 3 meters headphone cable. but that alone doesn't mean we can't find devices and usage conditions that are far enough from ideal to make it seems like going balanced is a big deal for headphones on a given amp.
     
  15. bigshot
    I guess I'm speaking about listening to music on a typical player and set of headphones in the home. Perhaps you're thinking of some other application.

    It's great to dot i's and cross t's but you have to be careful not to be so thorough that you give the wrong overall impression. In general, there's no point to balanced for home listening on headphones.
     
    Last edited: Jul 10, 2017
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