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newbie electrical question

Discussion in 'Amps and Cabs [BG]' started by romiso, Jul 8, 2001.

  1. Hi,

    I apologize in advance if this has been covered before -- an exhaustive search didn't turn up anything.

    I just got my first amp/cab setup -- a second-hand SWR Workingman's 300 amp and a brand new Ampeg SVT210 Classic cabinet.

    Periodically, I hear some distortion, followed by a loud pop, after which everything is fine (except for my nerves). Very disheartening.

    Some more info:

    - The amp has two speaker jacks -- I'm using the top one, although there's no indication to use one or the other.

    - I'm using 16-gauge speaker cable (1/4" jacks) to connect the amp to the cab.

    - The amp handles 4 ohms, and the cab is an 8-ohm (just stating the obvious)

    - The amp did not come with an AC power adapter -- I bought a new one. I assume all three prong (male and female) adapters handle the same amount of current.

    - The amp is plugged directly into the wall.

    - There are a good number of electrical devices plugged into the room -- including a fan and computer. It is an old house with what I assume to be pretty old wiring.

    My guess is that the wiring in my old house doesn't like the power-hungry amp, and that getting a power strip with a surge protector will do the trick. But I wanted to make sure I wasn't overlooking anything. I suppose there's a chance that there's a problem with the AC adapter, but I highly doubt it.

    Any assistance you could provide would be very greatly appreciated.

    Many thanks,
  2. Brad Johnson

    Brad Johnson Supporting Member

    Mar 8, 2000
    Gaithersburg, Md
    Do the noises coincide with anything occurring in the house, like AC, a refrigerator or freezer or a furnace kicking in?

    A surge protector is a good idea for electrical equipment but I have a feeling you may be experiencing an under-voltage situation, which a surge protector can't address. You need a power regulator for that and last time I checked they weren't cheap.

    There could also be something wrong with the amp or your bass (is it active?). Does it happen frequently? If it's easy to reproduce, can you try your gear in another location (not your house)?
  3. Brad,

    I think you're right -- although I can't guarantee that it happens when the refrigerator turns on, I know the lights dim when it does, and I imagine that that's what it is.

    I'm looking into UPS devices and the like -- the ones I saw were under $200 -- I don't know what you considered "not cheap."

    To me, a UPS is a good investment, as I can also plug my computer into it.

    Thanks for the good advice...

    -- Robert
  4. the cheapest UPS i know of is $ 90
    300w ups
  5. AllodoX,

    How much wattage do I need if I only plan on plugging my amp, and possibly my computer into it?

    I'm thinking of getting a UPS with automatic voltage regulation (it monitors the incoming power and regulates as necessary), which run a little more than the straight battery-backup boxes. Just need to know how much power it needs to be able to handle...

  6. Consider using voltage regulating equipment for your bass amp instead of a battery backup UPS. There is a big input power difference between a computer and a bass amp. I install UPS units as part of my computer consulting business, and these must be sized correctly for the amount of power the protected device will draw.

    A bass amp capable of drawing 750 to 1800 watts is going to require much more than an entry level UPS. Calculate the maximum VA (volts x amps) your bass amp will draw, and use this to size your power equipment. Volts are assumed to be 120 VAC for this calculation. For example, 1800VA is 120 volts x 15 amps.

    As for your popping, etc, try plugging your amp into a separate circuit in the house. Check the breaker box and see if your present circuit is on the same breaker as the kitchen, laundry, or air conditioning. If so, you may be experiencing transients when heavy load devices turn on and off. Last, your house itself may be under powered. My old house only had 100 amp service and this subjected everything in the house to transients when the air conditioning kicked on and off. I installed 200 amp service and fixed that problem.
  7. CYoung


    Nov 30, 2000
    Gainesville, FL
    You may also have a ground leak, which is common in older houses. Radio Shack has a cheap tester that can verify this. Fixing it, though, is a job for a qualified electrician.
  8. Every musician should have a power outlet tester. This is a standard $5.99 stock item at Radio Shack. It should be used at EVERY gig you play to make sure you don't get yourself killed (it does happen) from miswired power. Test both your amplifier and the PA amplifier, as musicians get hurt using their bodies as bridges between mismatched PA and amplifier power.
  9. jcadmus


    Apr 2, 2000
    Agreed, with gusto. Even if you don't killed, you can seriously, seriously screw up your gear.

    Heck you don't even need to go to Radio Shack -- you can get them at Walmart. Keep one in your gig bag and check the receptacle before you plug in EVERY TIME!

    Think of it as your six-dollar insurance policy.
  10. Thanks for the good replies all...

    I'm off UPS as a solution -- I don't think it will handle the power.

    Unfortunately, this is just a rental -- our entire apartment runs off of one breaker -- we hope to move soon. For the time being, I'm stuck with the electricity we've got.

    I did some more research and found a couple of more solutions:

    -- Sutton NETSAVERS LC1250.
    -- ACP 1250W line regulator.

    People seem to be using these successfully in studios with power amps, so I assume they'll work for me too. The Sutton goes for about $175, the ACP about $125.

    Anyone with any experience with these?
  11. APC is a big name in UPS and power regulation. Furman is another, but I think they might be exclusive to rack mount gear. All my experience is with APC, and it is all good experience.
  12. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Romiso, I think you probably have something wrong with the amp. Maybe something intermittant. An intermittant fault in the power supply might cause one or both supply rails to sag dramatically, causing the audio circuitry to clip prematurely. When the fault goes away, that could certainly cause a pop.

    An intermittant in the audio circuitry could also cause the problem you describe.

    I don't think a UPS or power conditioner would help, even for an amp in perfect working condition.
  13. I'm going to have the amp looked at this weekend. I encountered the same problem last night at a friend's house with "modern" wiring. Hopefully nothing major.

    Thanks again for all of your assistance...
  14. Just wanted to report a happy ending to my saga.

    The person who traded me the amp agreed to take it back. I came home with a nice used SM400. No snaps, crackles or deafening pops, and the sounds I'm getting are amazing.

    Thanks again for all your help -- sorry I wasn't more suspicious of the amp in the first place.

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