Humidiity, Hum and Heat wave?

Discussion in 'Pro Audio' started by Guest, Jun 11, 2008.

  1. Guest

    Guest Guest

    Hello,

    We recently had a heat wave on the East coast starting on Saturday. That
    same day I turned on my home recording computer system and had a nasty hum.

    I ripped apart the system and isolated the hum between the power amp and the
    speakers. I have a Hafler TA1600 power amp. If I plugged one speaker into
    the amp with no input signal, the hum was there.

    I've been reading up on ground loops and such - but they all talk about
    mismatched ground across electrical components. Can I have a ground loop
    between an amp and "just" speakers"?

    Does humidity in the air cause hum somehow? Can I get fancy speakers to
    eliminate this? Or maybe my speaker wire shielding is bad?

    The heat wave broke last night - humidity is back to normal for NJ. And the
    hum is gone....

    Thanks in advance,
    bruce
     
    Guest, Jun 11, 2008
    #1
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  2. Guest

    Scott Dorsey Guest

    No, because the speakers are not grounded. A ground loop is when there are
    multiple ground paths from any given piece of equipment.
    No, you had a power supply capacitor fail in the Hafler. Get it fixed.
    Or else you have an internal ground connection that has come loose.
    It'll be back.
    --scott
     
    Scott Dorsey, Jun 11, 2008
    #2
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  3. Bruce wrote ...
    Meanwhile, here on the west coast (at least where I am in southern
    Oregon) we are unusually cold. We've been burning wood in the stove
    to keep the house warm at night (and several days, as well).
    If NOTHING was connected to the amp but the power cord
    and the speaker(s), then you should have no ground loop(s).
    This is assuming that you don't have your speaker wires
    grounded anywhere (accidentally?)
    Not as you are describing.
    No. Speakers only reproduce what the amp is putting out.
    Speaker wires do not require shielding unless you have an
    unusually severe RFI problem.
    I would strongly suspect that something went wonky with your
    power then. Most equipment doesn't like operating properly
    when the power is much lower (or higher) than the nominal
    mains voltage (120V in North America).

    If the power is doing things that crazy, I would be concerned
    about my electronic equipment. I would at least be monitoring
    the power mains voltage to be sure I wasn't frying my stuff.

    If the hum *had not* gone away, I would have suspected
    the combined effects of age and extra heat to have dried out
    one or more of the electrolytic capacitors in the amp.
     
    Richard Crowley, Jun 11, 2008
    #3
  4. Guest

    GregS Guest

    You didn't specify exactly what you did. Were the inputs removed completly or just
    shut off. You could try headphones or a local speaker. Does the amp have a ground
    plug ? A speaker is sorta ground or the ground at its working position which may be different than
    the amp ground. Most electrical components are isolated from a wood cabinet, but you never know.
    Its not likely electrostatic noise can affect a speaker, but currents
    through the signal chain can cause current noise.

    greg
     
    GregS, Jun 11, 2008
    #4
  5. Guest

    Guest Guest

    I disconnected everything - mixer, computer, amp.

    I moved the Hafler amp to another room with 1 speaker attached and there was
    still hum. There was not any input into the amp.

    I read that humidity can cause resistance in ground and then thought. most
    studios are usually pretty cool in the control room. So, I was thinking
    that the humidity somehow resulted in this.

    Thanks.
     
    Guest, Jun 11, 2008
    #5
  6. Guest

    Mark Guest


    low line voltage can cause hum in an amp with marginal power supply
    regulation..

    running lots of air conditioners can cause low line voltage

    Mark
     
    Mark, Jun 11, 2008
    #6
  7. Guest

    jakdedert Guest

    You've either, like Scott says, have a filter cap going out; or (I think
    more likely), have something in the amp which is corroding. The excess
    heat/humidity caused a temporary bridge between two things which should
    not be connected...or caused something which should be connected to
    become intermittent.

    Check for dust or other contamination in the amp which could become
    slightly conductive when moist. Clean all that out (if present) with a
    vacuum or blower. Then check every mounting screw, especially ones
    which hold down circuit boards. Finally clean every control/switch with
    a good contact cleaner. Most people swear by Caig products. Expensive,
    but worth it.

    If it never comes back, it was one of the above. If it does, a clean
    'operating field' will make further dx easier.

    jak
     
    jakdedert, Jun 11, 2008
    #7
  8. Guest

    Eric B Guest

    Quite likely if you checked your lines voltage you were under going a
    brown-out.
    Eric B
     
    Eric B, Jun 11, 2008
    #8
  9. Guest

    Paul Stamler Guest

    <<low line voltage can cause hum in an amp with marginal power supply
    regulation..

    running lots of air conditioners can cause low line voltage>>

    And that's usually the cause of hum during heat waves: the line voltage goes
    low, the unregulated DC voltage drops, and there's no longer enough voltage
    across the regulator for it to regulate properly.

    This usually happens in equipment handling low-level signals, though, not
    power amps. Most power amps have unregulated supplies, so the only result of
    low line voltage is less output before it clips.

    Some power amplifiers, though, have a regulator for the input sections. Does
    the Hafler? If so, that'd explain the problem. And it would indicate that
    the amp isn't broken, just not designed for extreme low-line conditions.

    Peace,
    Paul
     
    Paul Stamler, Jun 12, 2008
    #9
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