SS amp and a "pop" when powered up?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by 3Sides, Oct 1, 2006.

  1. 3Sides

    3Sides Member

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    I just got this Marshall acoustic amp (used) and when I power it up there is this loud "fizzy pop" that happens. It only lasts a second, and then the amp is fine and functions normally. It concerns me because in the past, electronic devices that have exhibited this type of behavior died within in a few months.

    Any ideas what it could be? A short, moisture exposure?
     
  2. donnyjaguar

    donnyjaguar Member

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    This is more common than you might think. Many home hifi amp's have a muting circuit which delays the sound to the speaker for a second or two after powering on. If I had to guess, and that's all I can do really, I'd say one half of the output section is coming on harder and faster than the other and charging up the large value electrolytic on the output. Then as the other half of the push-pull output section starts conducting it pulls it back down to 0V (or somewhere near there). As for a fix, well give the complexity of many solid state amplifiers it would call for more detailed troubleshooting on the bench.

    Of course, it could be that this is normal operating for this amplifier too. Try turning it on with the volume all the way down. If this helps then the above is not the problem and you have something similar happening in the preamplifier chain.
     
  3. Big0range

    Big0range Member

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    I've got an SWR California Blonde acoustic amp, all solid state. The owner's info specifically addresses the "pop" on startup and says it's perfectly normal. I think it's no big deal.
     
  4. 3Sides

    3Sides Member

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    It's an 80 watt stereo amp. The only thing I could compare it to was their 50 watt mono amp, and that was dead silent. The noise is independent of the volume or controls.

    Maybe the stereo operation is causing one half of the output section is coming on harder and faster than the other and charging up the large value electrolytic on the output as donnyjaguar mentioned?
     
  5. ronin32

    ronin32 Member

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    When I was trying out acoustics at a guitar shop, the worker was pluging in the guitar, fliped the switch and said "Wait for the pop and your good to go." It was a new Fender amp, dont remember which one but it did it eveytime I would flip it on.
     
  6. donnyjaguar

    donnyjaguar Member

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    Hi 3sides, does it do this on both channels? If so, its probably normal operation. Do you have a schematic you can share? If you're feeling brave I can almost certainly suggest an appropriate modification to get rid of this annoyance.
     
  7. 3Sides

    3Sides Member

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    If by both channels you mean both speakers at the same time, then the answer in yes. It technically only has one channel.

    I don't have a schematic, but i will try to locate one.

    Thanks
     

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