Axiom Home Page Forums General Discussion Technical Questions Humming JBL subwoofer.

My sister-in-law's JBL Bass 20 sub has a hum. I tried disconnecting it from the receiver - still hums. I tried moving it to other outlets in the house - still hums. It has a 2 prong power cord. Think I should try using a 3 prong cheater plug?

Interesting slim profile sub. It looks like the Bose bass modules but it has two 6"(?) down-firing drivers on bottom.

Oh, and the humming isn't caused by the Winnie-the-Pooh toy that I shook out from the port. Amazing what people will stuff into those ports, eh?

Try the cheater plug. That worked like a charm on my VTF2.

A cheater plug sounds like something you buy for an adulterous wife.

for an adulterous wife, i would buy a box of 12 gauge 2 3/4 inch lead slugs.

bigjohn

I hate to be a nag here, but...

Defeating the power ground is dangerous - why not try the simpler solution of a ground lift first? Break the ground wire on the interconnect - no ground potential difference, no hum - sometimes.

Bren R.

BigWill, is it possible the humming stems from the sub not knowing the words. I apologize - I just could not help myself.

Perhaps you should read a few self-help books.

OK, can someone explain that a little further? I don't get it.

Hum comes from a difference in ground potential - ie: the sub "ground" may be floating at

*WARNING - HIDEOUS OVERSIMPLIFICATION*

2 volts, while the amp "ground" is at .1V for whatever reasons - different house paths to ground, but that's a book in itself... it's this differential that creates hum.

One way of killing the hum is by breaking the AC ground connection on the sub, so it's AC ground is determined by the amp AC ground through the signal return (let's assume a coaxial interconnect and call it the shield) - this works because the sub will get its ground "level" from the amp, the problem is the shield isn't heavy enough (at least 16ga.) to provide the adequate shock protection in case of a short - will take a dangerous amount of time to trip a breaker, or worse, may act as a fusible link and simply burn out while you stand there doing the 115v funky chicken in a pool of your own urine.

The safer way is to "lift" the signal ground, ie: connect the shield only on one side of the cable, it breaks the ground loop and allows the safety ground to remain intact on the sub for shock prevention.

Quit looking at me like that, audio isn't passed on the shield (but video is - don't try this with a video cable of any type - whether composite or component!)

Bren R.

shield?

Shield - again, I said assuming a coaxial cable would be the shield, signal ground, signal return, that with hooks up to the part of the RCA that don't look like a boy-part.

ie: your cable, if you made it yourself would have the center pins connected at both ends and the other connected only at one end.

Someone get me a napkin and a pen.

Bren R.

I think I may get it (BTW, thanks for the help everybody - my friends and family all think I'm some sort of audio/video genius due to the knowledge I've absorbed here in the past year ). If I were to disconnect the RCA plug from one end of the coaxial cable and reconnect it (sans the outer layer of metal shielding) I would break the ground that exists on that line. The sub would then ground itself via the power cord and the humming should stop.
Any special tools needed to reconstruct the end of that cable?

I wanted to ask, "Help with my sister-in-law's humming box?", but I was afraid that might be crass.
Would of made it far too easy for you hooligans, anyway.

What?! Your s-i-l has a kazoo? Can I have one, too?

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Oh, and the humming isn't caused by the Winnie-the-Pooh toy that I shook out from the port.

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Maybe the humming is caused by the Tigger toy that still IS in there??? Wasn't he the one that liked to bounce?

Actually, after thinking about it, I don't think the interconnect is the problem. The humming persisted unchanged after I completely disconnected the sub from the receiver. I even moved it to a different area of the house - still humming.
Is there a safety issue with using a cheater plug long term? I REALLY don't want to burn my s-i-l's house down.

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Is there a safety issue with using a cheater plug long term? I REALLY don't want to burn my s-i-l's house down.

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Not so much a fire hazard as a shock hazard... like if the owner of the Tigger toy pours a pitcher of iced tea into the port and starts doing the 115v mambo. Try the ground break, see if it solves the hum - tells you whether or not it's a ground issue, it could just be a noisy amplifier circuit, since it's not exactly a high-end piece of technology.

Bren R.

bigjohn,

I thought everything was BIG in Texas...so overkill would have been more the theme...10gauge 3"mag/ never mind a claymore would be better.


Semper Fi

unfortunately, i dont have a 10 gauge.. i dont even know if they make them anymore?? my papaw used to have one when my dad was a little boy. he sold it a lot time ago.

he used to tell me stories about it. they had the 10 gauge mounted to the front of a 12 flat bottom boat. they would troll up the river channels and blow turkeys out of the trees that were roosting. papaw said that 10 gauge would rock that boat back in the water about 5 ft everytime they would fire it. now, that is WAY illegal now, but back then, it was out of necessity, they had to eat.

bigjohn

MMmmm, I thought we were bad in Louisiana. Riding in a boat blowing up turkeys......now there is a thought.


Semper Fi

Will,
As you've said, it hums even when disconnected, so it cannot be a relative grounding issue between components. Done with that one.
You've also said that it has a 2 wire plug, which I think some of the other responders have missed. Using a cheater won't change the grounding worse than it already is - it's not using the dedicated ground pin. If the 2 wire plug is not polarized, then just try flipping it and see if the hum goes away. (I bet not). But I assume it is polarized and you cannot do that. If you can use the cheater and IT is not polarized, then you can try the same thing. Perhaps the JBL is wired wrong inside. At least it would be easy to check with the cheater routine. You won't set the house afire with that test.
Good luck

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You've also said that it has a 2 wire plug.

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Whoops... I missed that on the first readthru.

Bren R.

You might have some other electrical device plugged into another outlet in the house causing the problem. Anything with a large motor, or even a small stepper motor, can cause noise to be induced on the line.

2 things to try:

Turn off every circuit breaker (or remove every fuse) in the main panel, except for the one that the sub is plugged into. Make sure that the sub is the ONLY thing plugged into the 1 remaining circuit. If the hum goes away, turn the breakers back on one by one until the hum comes back. Then, you will have an idea where to look (if your panel has labels).

Second (maybe 1st) verify that your main electrical panel has a thick, bare, copper wire coming out of it that attaches to either a water pipe on the inside of the house, or a copper rod stuck in the ground on the outside of the house. If you don't see one, or if the connection you see looks bad, call an electrician. Your whole house could have a floating ground. If you have cable TV, it should also be grounded. Noise can come in on the ground (shield) as well.

(I forgot to ask... Are the AC grounding requirements in Canada similar to those in the U.S.?)

Good luck,

Thanks guys. I'll study those suggestions in the morning when I'm more coherent. I know the plug had one blade larger than the other (polarized?), so that's out. Before trying the circuit breaker I may just take her sub back to my house and see if it hums here. Should that be the case... I'll sell her my EP350 and get an SVS 20-39+.

I forgot to ask... Are the AC grounding requirements in Canada similar to those in the U.S.?

Don't quote me on this but I don't believe code here allows for a direct earth ground rod. I've seen them in pics from the states, only time I've seen them here is back in the aerial days for grounding antennas (and grounding camper trailers)

Bren R.

Just dug out the Canadian Electrical Code (the wife's a Sparky ... sorry, Electrical Engineer). You can use a grounding electrode (rod) or, as in many cases, the ground wire is tied to the water main. As long as the wire from the panel to the ground point is continuous - no breaks, no joins.

Sean

Hate to rip this one off topic Sean, but I think the original question has been answered... was going to pick your wife's brains on something.

Started replacing plugs in the garage - four of them plus five light fixtures and the GD opener are on one circuit, one single plug (the natural place for you to plug in a block heater) is on another and is currently dead for whatever reason - I didn't look too closely yet.

Traced back the wiring - it's all 14-2 or 14-3 copper... all the way back until the buried cable coming into the garage from the house, which is, of course, aluminum (did anything GOOD come out of the 70s?).

Since I'm paranoid about AL wiring, I ran out and got a specifically listed CU/ALR duplex outlet for that one. So I have - 12-3AL coming up into the garage, the red conductor energizes the outlet I'm replacing with an ALR listed outlet and continues from there as copper as I explained. Since I usually replace aluminum wiring and have never really tried to make it safe, unsure how best to deal with it.

I'm under the assumption that the safest way to make a connection between AL and CU is through an AL rated outlet rather than pigtailing with a marrette. So the red conductor as it sits should be reasonably safe. Now the black side is pigtailed with a Marrette in the same box onto the copper run that takes it to the box it feeds, which if I understand correctly, can lead to fire (oxidation occurs, resistance goes up, hot spot, marrette melts and the spring turns into a cigarette lighter). Does it make any more sense to use the top and bottom plugs in the duplex (with the hot tab broken) to make the transition? Or will this lead to overloading the neutral? Would it be any safer than the way it's pigtailed now?

Bren R.

Bren

Katherine is off at a guide camp for the weekend so I won't be able to pick her brain until Monday. Besides, for some reason, I'm the one that does all the wiring around the house (unfair I say!!). However, in the meantime try the following link that deals with that exact issue. If you have any further questions, send me a PM and I'll see what I can do for you.

http://www.region.halifax.ns.ca/Fire/pages/wirebasics.html

On a different note to the board. My family and I will be moving shortly to Alberta, I'll have to pick up the Axiom board from there.

Sean

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pigtailing with a marrette

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hehe... I had to look this one up - I'd never heard that before.

Oh, you mean a warnut? (that's good ol' boy for wire nut).

Is the electrical connection box on a motor called a "peckerhead" in Canada?

Marrette, wire nut.....I'd heard it called a Dutch lock before but have no idea why.

Further to my garage wiring dilemma...

The aluminum turned out to be coated copper (experimental BX stuff used in the 70s, and as safe as copper) but I did find out one of the two circuits out to the garage was dead all the way back to where it enters the house. Well, hell... I wanted one dedicated circuit for the block heater and another for the lights, etc.

Finally got some time to really look into it last night... broke open the junction box that carries the circuits and... hmm... three neutrals tied together, red hot to red hot, black to... waitaminute... there's a switch circuit in here... and it runs into a cold air return?!? that's not code... and it continues to a switch on the razor plug in the ensuite bathroom... ahh, I get it... one of the previous owners wanted to be able to switch his interior car warmer on when he got up in the morning.

At least now I can tear that all out.

Bren R.

There's a thought. Any plenum rated speaker wire out there?

A quick Google search seems to point to a lot of Belden, Monster and Canare products that are plenum-rated and UL-approved.

Bren R.