I have a jbl front firing subwoofer about 7 years old and just starting loud humming sound when plugged in and in the auto on mode. tried sending music singnal and still half sound mostly noise. seams like amplifier problem just not sure what to check for. I can take it apart and solder or replace or check whatever.any help I would greatly appreciate. thanks.tc.
Winslow is correct. It is likely to be a bad capacitor on the power supply. There should be two large capacitors on the power supply circuit. These capacitors filter the 60Hz waveform from the power. These will be the two largest capacitors in the entire system. The bad capacitor is probably bulging. For safety, you should replace both capacitors with exactly the same uF, voltage, and temperature ratings. Don't use anything smaller than the ratings of the current capacitors. And don't waste your time going to RadioShack, they won't have any big enough capacitors. It would also be a good idea to check any resistors that are near the capacitors, if you see a slightly larger resistor that is burnt, then you will probably want to replace it.
Buy a replacement "plate amp" from parts express (google it). I replaced mine and it was a vast improvement. I think I bought the 100 or 150 watt one but bigger will yield better results. If the jbl is the model bp12 it is a killer sub with a flawed amp. Point being it IS worth changing the plate amp. Changing the plate amp will require a bit of carpentry with a jigsaw to enlarge the mounting opening on the back. Remove the speaker while doing this. Also wouldn't hurt to upgrade the speaker wire between amp and driver to monster cable or equal.
Good chance it's the power supply; a capacitor there, the large one, may have gone. These things age and when they go, there's noisy power to the amp circuit and ... well, that may be what you're hearing.
You should check your audio wiring, too. That woofer could be picking up a 60Hz hum from the AC mains and amplifying it. Maybe you can try another spkr on same cables and see if hum is in your woofer or elsewhere.
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It is possible that the amplifier within the unit is faulty; The best you can do is to put the woofer ON for about 12 hours so that if there is any chance of any capacitors being faulty or has electrlytic drying.
if this wont solve the unit must be opened to check the amplifier. Possible failure of the input source selector as the woofer is humming.
It sounds like you are describing an earth loop problem. I won't go into detail in this post, but try an isolation test first. disconnect everything from the reciever except the sub and try connecting say a BATTERY powered mp3 player or cd player to minimise connections to the electrical mains earth. you could also isolate things by taking your sub to a friend's house and trying it on their system. If it is an earth loop use a process of elimination to find out which two pieces of equipment causes the earth loop. then apply filtering. you can buy earth loop isolation transformers for about AU$26 and I've used one on my sub myself. Theyhave RCA (phono)plugs on each end and they connect inline with the signal cable to the sub amp.
as for the thumping sound it might be the speaker protection circuitry cutting off the amp to protect the subwoofer speaker from damaged. This might be triggered if the earth loop sound is causing the sub amp to overload and clip.
Failing this there might be a dried out overheated electro capacitor in the amp circuit causing the hum. Hav a chat to your local electronics person, who should be able to spot it! Hope this puts you on the right track Happy Hunting!
have you checked your music source? Some systems like computers have a sort of output first before normalizing, which isn't your powered subs or powered amps problem. Try plugging in a regular solid state player like an ipod if the humming is still there when automatically turning on or off...
There is actually some good news. I had this problem with my PB10s (1 have 2 PB10s and 2 PB12s) It is one of 2 things, the first is that it could be a capacitor and resister combination on the amplifier board (which was the fix for our PB10 with the same problem), or 2nd, the AMP IC, which is not available for the PB12. hmmm
Hello, Jesse. I doubt I can help, but there is at least one SIMPLE thing you can try - with maybe a 10% chance it wil return your unit to normal:
Unplug the unit for 30 seconds, then plug it back in to a DIFFERENT outlet.
Oh, yes - there are NO fuses or other "reset" devices.
I'm sorry I couldn't offer you more help.