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Thread: What are the benefits to things that have balanced differential inputs?

  1. Back To Top    #21

    Re: What are the benefits to things that have balanced differential inputs?

    Just thinking out loud here, and trying to do that scientifically.
    Here are the two parts that actually differ, to help think through it:
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    Click image for larger version. 

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    The balanced receiver end, is same for both:
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    In the coax cable, the signal and shield are separate at the source, and therefore from the perspective of the balanced receiver, "lo" and "sh" have to be soldered. Also, on the source end "shield" is often at the ground potential. And on the receiver end, pin 1 is grounded - therefore pin 2 is also.

    On the shielded twisted pair (or quad), they show the shield and one conductor soldered at the source. Then at the receiver, you have 3 distinct pins [with only pin 3 grounded, in the receiver].
    Overall, it's true pin 2 is also grounded (because they are connected, on the source side), however I think it has to factor in the length of the cable and the assumption that the noise is entering somewhere during that cable length.

    That could result in the noise being on pin 2 but not the double-grounded shield, and therefore the balanced circuit able to remove it - but since we're not dealing with a balanced differential driver or inverted signal on pin 2, I'm not yet understanding the removal or rejection mechanism fully.

    And actually - maybe I'm thinking of that wrong anyway. There's only one op amp in the receiver and I think actual balanced receivers require 3, with two of them doing that noise removal by inverting and combining...
    But regardless I'm not seeing how the noise is attenuated. Has to do with pin 2 not being grounded...
    Last edited by geolemon; 05-27-2021 at 07:54 AM.

  2. Back To Top    #22
    Noob Jdunk54nl's Avatar
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    Re: What are the benefits to things that have balanced differential inputs?

    I am glad I am not the only one struggling with this.

    I did start a post on ASR as well, some more people in the "industry" live over there so thought it might help:

    https://www.audiosciencereview.com/f...rential.23746/
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  3. Back To Top    #23

    Re: What are the benefits to things that have balanced differential inputs?

    I was in electrical engineering for three years but never finished...

    Had a too-good-to-waste opportunity with some of the best data warehousing and business intelligence pioneers in the late '90s and that changed my whooole professional and education direction.

    So - back to this stuff just being a hobby!

    25 years later... My EE teachers would be disappointed with me. I still feel like I should know this.

    Sent from my LM-G820 using Tapatalk

  4. Back To Top    #24

    Re: What are the benefits to things that have balanced differential inputs?

    Quote Originally Posted by geolemon View Post
    I was in electrical engineering for three years but never finished...

    Had a too-good-to-waste opportunity with some of the best data warehousing and business intelligence pioneers in the late '90s and that changed my whooole professional and education direction.

    So - back to this stuff just being a hobby!

    25 years later... My EE teachers would be disappointed with me. I still feel like I should know this.

    Sent from my LM-G820 using Tapatalk
    Seriously thinking about going to school for EE. Thoughts?

    Sent from my XT1710-02 using Tapatalk

  5. Back To Top    #25
    Noob Jdunk54nl's Avatar
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    Re: What are the benefits to things that have balanced differential inputs?

    What career do you want from an EE degree?
    2014 F150 Limited -> Kenwood DDX-9907xr -> Helix DSP.2 -> Alpine PDX-V9 -> SI M25 mki in Valicar Stuttgart Pods, Rear SB17's, Sub SI BM MKV's in MTI BOX. Alpine PDX-F6 -> SI Tm65 mkIV, SI M3 mkI in Valicar Stuttgart Pods

  6. Back To Top    #26

    Re: What are the benefits to things that have balanced differential inputs?

    I think it's a great career, with a few caveats:
    1) I found it more difficult than I anticipated to get started - I was shocked that the majority of the class already knew quite a bit... Either their fathers were electoral engineers, or they'd been raised building electronics like Heathkits. It was impressive - but the teacher taught to their level. I thrive with my feet in the fire (it's why I was recruited by the BI IT consultant team) but it was hard.

    2) There's a range of careers, and what you land in can depend on your school. There are electronics repair people - those jobs don't pay too well but lots of people find that fun. I wish I even qualified to do that - I have several old amps I'd fix!
    Actual electrical engineers can work on anything from consumer product development projects, to aerospace. A couple decades back I helped co-found an SMT contract manufacturing business, and slid into the role of manufacturing engineer, I programmed and set up and ran the solder printer, the pick and place machines, and the oven (ours had 7 zones, all programmable) and we targeted the aerospace and medical contractors - big money and difficult standards. We had to automatically (that one was mine) manually and X-ray inspect all the boards to guarantee if they were dosing anesthesia or up in a satellite, they'd work. Very different than consumer electronics.
    Other electrical engineers work on large scale power distribution - buildings, factories, power companies - I feel like the sky is the limit.

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    Noob Julian's Avatar
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    Re: What are the benefits to things that have balanced differential inputs?

    Quote Originally Posted by Jscoyne2 View Post
    Seriously thinking about going to school for EE. Thoughts?

    Sent from my XT1710-02 using Tapatalk
    Good job opportunities, I would do it. Just be prepared for how difficult it is. You will learn theory, start simulating circuits in software, and test on the breadboard in the lab. That is just the start. It is a very unique way of thinking. The best EEs have a near instant grasp when learning new things coupled with the creative mind of an artist. The best of both worlds.

    Look around you at everything electronic and the career options are many. I know an EE that works in product testing. They hand him a prototype and he does every stupid thing the end user might do to try to break it. Also knew a guy in VLSI circuit design.

    In college, we worked a bit in the lab on implanted sensors in the human body. And there is also the patent law side of it if you want.

    Im just Physics with some EE. Ive worked with LVDS, digital, and by presenting the differential signal at each side, the noise is subtracted out. That is the obvious theory. Beyond that, youd need someone who works specifically in that area to explain it. EE is specialized like everything else and is a pretty broad field in and of itself.

  8. Back To Top    #28

    Re: What are the benefits to things that have balanced differential inputs?

    there aren't any balanced line output sources anyway, so the start of the signal chain will be unbalanced (signal and shield on an RCA cable) and would need to have a conversion to become "signal, inverted signal and ground reference". that is where the 3 signals would come from, so that the reversion process of combining the "signal (+) and the "inverted signal" (-) would be combined after the "-" signal is inverted again to add constructively to the "+" signal, and the "noise " that is present in both signals, would have one half of it inverted, and then that would combine destructively with the + signal and be cancelled out, reducing the noise induced over the length of the signal wire. but we do not have that in car audio, so most source outputs are just signal and shield. that means if the shield is used improperly or does not shield enough, the noise and the signal are both amplified.
    kenwood had a cd player (KDC-X911) that had fully balanced outputs using RCA outs, where one RCA was the + and one RCA was the -. worked AMAZINGLY well, sadly, never caught on.

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