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Questions about low line voltage scenario

Discussion in 'Amps and Cabs [BG]' started by Lee Barker, Mar 19, 2009.


  1. Lee Barker

    Lee Barker Labor of evident value satisfies the soul. Supporting Member

    Oct 25, 2005
    Redmond, Oregon
    owner, Barker Musical Instruments, maker of the Barker Bass, No Longer In Production.
    I appreciate this resource for helping to solve problems. Here's mine:

    Church setting. I play through my own Workingman's 12. Over time, there are volume valleys--lasting minutes, and significant enough that I have to turn up the gain.

    I checked my instrument and had my tech go through the amp--nothing. One of our group works for a power co. (not the one in question) and he brought this monitor that plugs into the wall and randomly samples voltage and prints a report. Over two weeks, there were dips as low as 101 volts.

    While the combo was out, I subbed with my GK 400RB. At one point it dropped volume and made an audible (if you were close to the head, no music on) rhythmic chirping sound, coming from inside the head (not the speaker).

    I reported this voltage variance situation to the appropriate church committee, in writing, with copies of the printout, requesting resolution. That part is out of my hands and my control.

    My questions:

    1. Am I missing something, or are the voltage variances likely causing the volume issues?

    2. Am I risking damage to any of this equipment by using it until the issue is resolved? (I also have a GK BL300 and a Glockenklang Soul which I want to use there for periods of time to get to understand and appreciate them better.)

    Thank you in advance for the benefit of your experience in a similarly verified situation and your real world counsel about potential damage to any of my amplification stuff.

    Lee Barker
     
  2. I live in SE Asia and suffer from 'brown-outs' due to poor quality of supply. The electrical problems here in the developing world are fairly significant compared to the US, Australia, etc.

    I find that my power amp can suck juice to the extent the neighbours' lights dim ( :bassist: ) and the situation is always worse when everyone you share a supply with has their air conditioners on. I now have a few things that don't cure the problem but help.

    The first is a power controller in my rack that has a real-time voltage readout. So I can see if there is a problem.

    The second is a voltage regulator. It's big and heavy and mine doesn't correct low voltages, it just takes the spikes out.

    I also have some thick (2.5mm) flexible supply cables so I can take a direct feed from the fuse box in the event the venue's cabling is contributing to the problem i.e. long runs of narrow diameter, cheap cable to the power socket (not a problem in the US, I'm sure).

    Most sound guys here are experienced with this issue so when I play big gigs they have generally arranged in advance to run a dedicated supply to a high-wattage voltage regulator and I happily plug into that.

    I damaged an SWR head due to low voltage a couple of years ago. I was using it as a pre-amp and it started cutting out intermittently. This made me nervous enough to look into the problem further.

    The only suggestions I have are:

    - check the wiring - is it a long way from the fusebox and thin?

    - ask the ladies in the auxiliary to turn the fridges, freezers and urns off while you play :bag:

    Cheers
     
  3. Hi.

    First of all I'm not an EE, but a BEng mech, electrical appliances are only a hobby for me.

    1. The power supply in an amp is there to supply rail voltage(s) for the output devices. If the wall supply (rail) voltage drops, the power supply (OP device) draws more current to compensate and the output is kept at a constant level. At least in theory.

    Depending of the design the power supply can or can't keep up. If it can, the "over current" can cause overheating. If it can't the result is usually decreased headroom, ie. clipping, not a volume loss.

    If the amp is operated below the maximum output cabability of the design (PS/amp), there shouldn't be any noticeable effect in any way.

    2. No damage should occure, every modern quality amp has several different protective designs to prevent the exessive current draw to damage anything.

    What I think is happening (based to my SWR WM10") is that the hybrid chip is acting up.
    If WM12 uses similar chip(s) as WM10 that is. If it's a discrete design, one might be defective.

    Regards
    Sam
     
  4. Lee Barker

    Lee Barker Labor of evident value satisfies the soul. Supporting Member

    Oct 25, 2005
    Redmond, Oregon
    owner, Barker Musical Instruments, maker of the Barker Bass, No Longer In Production.
    The only suggestions I have are:

    - check the wiring - is it a long way from the fusebox and thin?

    - ask the ladies in the auxiliary to turn the fridges, freezers and urns off while you play :bag:



    Thanks Lindsay--interesting background. I know less than nothing about power conditioners, but my reading suggests you have to get into the $300 and over category to find the "fixes sags" feature--all those below that just deal with spikes.

    As to your suggestions: The building is less than 30 years old so I have confidence the wiring is to code. That said, there has been explosive residential development around it the last 5 years. One could wonder how many dryers are going on simultaneously with the inhouse freezer and coffee urns.

    My ultimate hope is that it is a power company problem and they can fix it at the pole.

    Then I read the next post from Sam, and I'm thinking, maybe the SWR WM12 has a problem (though that would not explain the GK acting up).

    I truly appreciate these thoughtful and helpful responses.
     

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