Connect with us

Signal noise?

Discussion in 'Electronic Basics' started by davidd31415, May 24, 2005.

Scroll to continue with content
  1. davidd31415

    davidd31415 Guest


    I am trying to troubleshoot a problem with an electro-dynamic shaker.
    There is a coaxial output from a computer to an amplifier and outputs
    from the amplifier to the shaker. I am sending a 15-150Hz 0-1V signal
    to the shaker.

    There was a "ground loop isolator" between the computer and the amp
    (coax converted to rca, then back to coax), which had been used to
    remove 60Hz line noise in the past. I know 60Hz is the AC line
    frequency but have not yet understood why this particular frequency
    manages to cause interference through ground loops so often; an
    explanation of that would be great here as well.

    What I am ultimately hoping to understand is what might be going on
    with the signal:

    The shaker is intermittently knocking and does not seem to be working
    properly (with THIS amp only). If the ground loop isolator is hooked
    up and I touch the shielding around the connectors with my hand, the
    knocking goes away (otherwise the ground loop isolator makes the
    knocking occur on a regular basis). I'm curious how my touching the
    connector could have anything to do with this? I would initially guess
    ground it has something to do with me being grounded, but to such a low
    voltage does my being grounded (through shoes) make a difference to the

    The knocking occurs intermittently when the ground loop isolator is not
    connected. I've hooked a Y up to the output of the computer and
    watched the signal with an oscilloscope (no ground loop isolator) and
    have not noticed anything strange there, but when the scope is hooked
    up and the input to the scope is disconnected (but the coax remains
    connected to the Y), the shaker starts knocking more often than in any
    other situation. I've also noticed that if I use the other (red) set
    of rca leads on the ground loop isolator (rather than the white), there
    is no knocking.

    I'm thinking there may be something wrong with the ground loop isolator
    since only one set of its leads causes regular knocking, but seeing as
    the knocking occurs even without it and my touching it effects it, I've
    though perhaps electromagnetic waves or something else may be involved
    here as well.

    Any input would be appreciated! Thanks,

  2. Line powered equipment often leaks significant current into ground
    through either resistive paths or capacitive ones. This current
    alters the local potential of ground at line frequency. If you
    amplify a voltage compared to local ground, and it was generated with
    respect to a different local ground potential, the difference between
    the two local ground voltages gets added to the signal.
    There is probably something in the vicinity that is radiating strong
    electric fields that the cable shield is picking up as capacitive
    current (probably where multiple cables run parallel). Your body adds
    a lumped capacitive load to that shield when you touch it. How is the
    cable shield on each side of the ground isolator grounded?
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day