Analog AC meter to subwoofer signal

Discussion in 'General Electronics Chat' started by Engineerer, Jun 16, 2015.

  1. Engineerer

    Thread Starter New Member

    May 22, 2013
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    Hi,

    I know that you can use atleast digital multimeter to measure subwoofer amplifiers output voltage with or without subwoofer connected. I would like to install analog panel AC meter permanently to indicate subwoofer level. Max voltage without clipping is about 40 VAC, so I'm looking vor 0-50V analog gauge. Do you see any problem with that? I have only high level signal accessible, no RCA.

    I also know that there are VU meters, but those require driver and it seems that ready made drivers can't handle 40 VAC. Thanks in advance.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Yes, you can connect an AC voltmeter directly at the subwoofer amp output.
    A VU type meter would be easier to read since it has a calibrated response to sound level, similar to the human ear.
    If the VU meter is too sensitive just add a resistive attenuator in series with the voltmeter input.
     
  3. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Should you opt against a VU meter be advised that, as per @crutschow, meaningful indication will require a movement featuring a logarithmic scale..

    Best regards
    HP
     
    Last edited: Jun 16, 2015
  4. Lestraveled

    Well-Known Member

    May 19, 2014
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    You can also use led bar graphs. There is a large variety to pick from on ebay. As HP suggested, go for the log or audio bar graphs. Do not get linear.
     
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  5. Engineerer

    Thread Starter New Member

    May 22, 2013
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    Good point about that logaritmic scale. Altough I mostly need that meter to see when I'm close to max power and clipping.
     
  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    I don't see the need for a meter to read the full voltage scale. a simple resistive divider could offer up a reduced voltage for a meter that accurately represents your true signal voltage level. divide by 1000 to get a zero to 40 millivolt signal and use a 50 millivolt panel meter.
     
  7. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    if the pointer "wiggles" to much due to the low freq nature of the signal a capacitor would smooth it and give a slightly delayed response with less jerk to the readings. 1 - 10 uf would be sufficient I would think.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    If looking for signal power peaks then you don't want to filter the signal very much since then you may miss the magnitude of the peaks.
    The natural inertia of a mechanical meter likely will be sufficient.
     
  9. alfacliff

    Well-Known Member

    Dec 13, 2013
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    you would have to go into the meter to connect capacitor to a point where the input signal was rectified.
     
  10. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    you're correct. I did not consider the sealed nature of chinese plastic units that are so prolific these days. "wiggle" while annoying, is not a condition that would prevent one from gathering the needed information the meter is providing.
     
  11. tcmtech

    Well-Known Member

    Nov 4, 2013
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    The simplest clipping indicator I know of is to put a LED and resistor across your amplifier's output devices and supply rails. When the LED goes out the amp is likely clipping or very close to clipping.
     
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