Buzzing subwoofer. 3 prong plug?

Jicafold

Active Member
So I have a JBL PB10 subwoofer. It makes a hum / buzz when plugged in without any audio connected. I've read elsewhere that this is 60hz interference. I've tried plugging this thing in everywhere in the house, extention cords, power strips, surge protectors, plugged in by itself, with other items. No change. When dismantled the sound clearly comes from the transformer. It's not so bad when its out of the box, its as if the box amplifies the buzzing. Sub works great and sounds great otherwise. Do you think it would help if I replaced the factory 2 prong plug with a 3 prong plug and soldered that extra ground in there? Thank you.
 
Is it a mechanical/vibrational hum/buzz, or is it a sound coming from the speaker driver? Seems to be the former from your post?

If so, I'd look at if there are any rubber washers or other isolation between the trafo and the chassis. It could also be the trafo delaminating perhaps due to age - not sure how old your sub is actually.
 
I disconnected the speaker, so the hum is coming from the transformer. I had my ear right up against the transformer and that is definitely it. I suppose I should consider some rubber isolators as you suggest. I was also considering covering it with some type of foam to absorb the noise. By the way when I took this apart the subwoofer + and - wires were backwards when compared to their marked connections on the board and the woofer. WTF?
 
It could be the amplifier inverts polarity, or it could be someone else was in and changed it. Hard to say.
 
Well, I put four rubber washers under the transformer as well as wrapped it with acoustic batting. No change. Still hums as loud as ever. Which brings me back to my original question, would installing a 3 prong plug with that extra ground help?
 
Which brings me back to my original question, would installing a 3 prong plug with that extra ground help?

If it is a mechanical hum from the transformer probably not.

Tinkering with ground may address electrical noise from the speaker/driver but this is a mechanical hum. It could be that the transformer has some loose laminations.
 
So in reading that manual, thank you by the way, I am in category B..."mild audible hum under all circumstances". I understand that they may consider this normal, but it is bothersome. However, it says replace transformer, not install 3 prong plug.

So if I replace the transformer can I just use any home audio 110 - 12v transformer?
 
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It's not a good idea to wrap insulation around the transformer. This will cause it to heat up more. Just replace the tranny with a direct equivalent. Call JBL, they may still have the part.
 
Where do you see 12V transformer?

Looks like +/- 45.7V rails to me, which I think suggests something on the order of maybe 70V CT.
 
I am not being "snarky" here, just a good soultion that has worked for me.
Having fixed several sub woofers with bad capacitors, their owners complaining "I hardly ever use it and now it is dead, I only had it for three years" (plugged in all that time).

Kill two birds with one stone- Plug your sub (and system?) into a good quality power strip!
You will fix-
A) Your hum problem.
B) Longer sub woofer life.

The transformer "hums" when plugged in to the AC line even when the sub is not "making music", and is therefore powered up (the transformer) AND generating HEAT 24/7.

The heat generated inside the sub box WILL reduce the life of the subs amplifier capacitors OVER A LONG TIME, even when NOT PLAYING, even if a relay cuts off the power to the amp when in "standby" mode there is STILL the enclosed trapped HEAT that "kills" the capacitors!

Use the power strip to shut off the sub when NOT USING IT.

Mark T. :music:
 
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