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Old 11th February 2008, 10:26 AM   #1
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Default Subwoofer amplifier

Just got a subwoofer amp. But when tried, fuse (T8amps, L250V) keeps on opening. Any help/suggestions will be greatly appreciated. By the way, the subwoofer driver give a loud popping sound then the power dies. Sub amp has auto on and off. Thanks
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Old 11th February 2008, 10:33 AM   #2
AndrewT is offline AndrewT  Scotland
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add a mains light bulb tester to the primary circuit. Switch on and tell us if the light bulb glows bright or dim or not at all.
If it still fails to start up, disconnect the low voltage power supply from the rectifier and try again with the light bulb.
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Old 12th February 2008, 01:47 AM   #3
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Andrew, appreciate your reply & assistance. My apologies, what do you mean by "add a light bulb?" Do you mean and ordinary light bulb attached to the main line? By the way, there is no switch between the cord and the amp- just a plug that goes straight to the amp. Can improper grounding do this? I'll take a picture and this would probably help you.
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Old 12th February 2008, 08:13 AM   #4
AndrewT is offline AndrewT  Scotland
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Search "mains light bulb"
wire it up permanently with a plug and socket and use it each time you start a new project or modify an old project or in your case want to test a damaged amp.
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Old 12th February 2008, 10:36 PM   #5
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Is a "Fast blow" fuse different from a "slow blow" fuse even if the same ampere (8 amps) and same voltage (250 volts)?
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Old 13th February 2008, 01:10 AM   #6
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Yes. There are rules to how much current a slow blow and a fast blow fuse should take before braking the circuit. In addition there are rules about the slow blow fuse in respect of how much current it should withstand (times its rating) without braking.

These rules are correlated to time: should blow within x milliseconds or should not blow before x milliseconds if a defined multiple "y times its rating" of course depending of if it is a slow blow or fast blow one.

So for a slow blow type the stipulation could be like this:"should not blow within x time if the current is 2 times its rating but should blow within x time if the current is 5 times its rated value.

Slow blow types are used for instance on the primary side of a mains transformer where the start up current is high before the current through it builds up a magnetic field that "opposes" the changing direction of the AC current.

Fast blow or even super fast blow types are more common when it comes to protect sensitive devices like semiconductors.

Markings in accordance with IEC: FF = super fast . F = Fast . M = Medium fast. T = slow.
TT = very slow.
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Old 13th February 2008, 02:33 AM   #7
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Thanks for that info. Indeed, very helpful for me who thought that it doesn't matter. Now, if I place a fast blow instead of a slow blow fuse, and the fuse blew, does that affect the circuit?
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