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Ground loop filter

Discussion in 'General Electronics Discussion' started by cjdelphi, Dec 11, 2015.

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  1. cjdelphi


    Oct 26, 2011
    The GLF is there to remove any DC bias it simply removes the annoying hum via a 1:1 audio transformer...

    I'm no Audio expert, at all lol... but just logically thinking about it, could an optoisolator be up to the same job? Or am I barking up the wrong tree?
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    The ground loop filter not only removes DC bias, it elaiminates the closed path for AC return currents as well - DC wouldn't produce a hum. The hum comes from the 50/60 Hz mains frequency currents flowing the path of least resistance.

    An optoisolator can interrupt the ground path, but is a very very very poor analog component. Optoisolators are typically used as digital parts, although analog optoisolators exist which, with a bit of circuitry around them can transmit analog signals with approx. 10-12 bit accuracy. For HiFi these are not suitable. You'd have to digitize the signal (A/D), the send it through the optoisolator, then convert it back to analog (D/A).
  3. duke37


    Jan 9, 2011
    I think I remember many years ago of seeing a circuit to transmit audio via a optoisolator. The idea was to use two identical isolators, one transmits across the gap and the other is used for feedback to adjust the drive so that the output matches the signal.
  4. GPG


    Sep 18, 2015
  5. cjdelphi


    Oct 26, 2011
    Ahhh got it, that fills in the gaps, I'm going to experiment out of curiosity sakes :) Thanks!
  6. AnalogKid


    Jun 10, 2015
    Yes, an optoisolator will work. The problems is that both the conversion from current to light, and light to current and non-linear and not complimentary. So as a simple interface device similar to a transformer, harmonic distortion is added to the signal. There are circuit design tricks to minimize this with standard optos, and there are specialty devices optimized for analog signal transfer.

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