# Sub hum? Anybody help?



## bcharlow (Dec 23, 2008)

I have a ULW 10" sub from AV123 with their factory substituted 500W plate amp. It has a low hum, particularly after many hours of standby, which may intensify when actually used for musical input. It's not the loud ground loop type hum, and all units are grounded to the same point anyway.

Any ideas?

Thanks.


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## tonyvdb (Sep 5, 2007)

If you unhook the sub from the receiver does the hum still exist?


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## bcharlow (Dec 23, 2008)

I'll check. Certainly when I power off the sub it quits.


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## bcharlow (Dec 23, 2008)

It lowers the intensity noticeably to detach both ICs from the receiver, each one successively lower. But it is only eliminated completely by turning off the power altogether to the sub.


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## tonyvdb (Sep 5, 2007)

It does still sound like a possible interference issue. Have you tried to run an extension cord from somewhere else to power it up.


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## bcharlow (Dec 23, 2008)

No. Last time I plugged it into the other duplex down the same wall, I got serious ground loop hum. I have two other obvious options: same power strip (all star wired) but second duplex; Isobar filtered strip which is plugged into this same main analog strip.


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## tonyvdb (Sep 5, 2007)

The Isobar is a good option even if it means buying a second one just for the sub.


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## bcharlow (Dec 23, 2008)

I used to have it on the Iso. Maybe it was a bad idea to swap? i'll try it that way and let you know. Thanx.


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## bcharlow (Dec 23, 2008)

Nope. The Isobar doesn't make any difference. Neither does the other outlet on the main strip. Seems as though as long as this thing has power it makes this low hum; power off, no hum. Changing the ICs doesn't do it either. Pulling both ICs out, though, lowers it by about half - that is, when it's not connected to the receiver directly.


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## tonyvdb (Sep 5, 2007)

I am not sure why you are saying both interconnects why do you have two of them? I would change the ICs with another one and see how that helps otherwise you may have an issue with the amp its self. People have had this sort of problem and sometimes rearranging the cords the way they lay on the floor can stop the noise.


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## villain3g (Aug 6, 2009)

my two powered subs used to hum quite bad. i went to the hardware store and picked up a pair of three to two prong adapters. this eliminated the ground. No more hum. worth a shot for a couple bucks.


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## bcharlow (Dec 23, 2008)

Ooops! My error. The unplugging of either or both ICs does NOT appear to reduce the hum at all. (I have L & R hooked up to the receiver, which is the way I've always done it, but don't know that it effects the sonics truly.)

In fact, nothing other than strictly powering OFF does the trick. If the green power light is on, I get the hum (that includes when it's on standby for signal mode - when red it's not humming).

I'm going to try lifting the ground altogether temporarily and plugging into another outlet that I know is on a different breaker.

Let's assume nothing but the power being OFF makes any difference, after all this. Then does it mean that I have a defective sub amp? If so, how would one repair that, as AV123.com is now out of business permanently!


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## bcharlow (Dec 23, 2008)

OK, now I've tried everything I can think of to determine if it's a ground loop. Plugging the sub into any outlet other than the one shared by all my audio results in a clearly loud ground loop hum. 

Lifting the sub ground does not diminish the initial hum problem at all.

Plugging into any outlet on my strip or isobar does not diminish the initial hum problem at all.

Unplugging the ICs that carry the signal to the amp does not diminish the initial hum problem at all.

Disconnecting the coax that feeds my receiver's FM input does not diminish the initial hum problem at all.

The hum clearly emanates from the sub's driver, though it may originate with the sub's amp too. The hum is low but annoying from when any power is drawn by the sub amp, period, but not when it's on standby and the power draw light is red, or off. Unfortuantely, the hum is audible from my seated listening position (must be a good node for my LF!)

I cannot say whether the hum is same or worse as the sub amp is on and drawing more power, just that it is audibly present whenever the sub amp draws power, even without LF signal.

So I'm left wondering if it's: a) a problem with the sub amp itself, or b) an absolute polarity issue.

Can anybody help any further?


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## villain3g (Aug 6, 2009)

did you give my suggestion a shot? or did you just run a cord to another room? i had the same problem and nothing would fix it except taking the ground out all together.


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## soundman85 (Apr 10, 2011)

+1 on the two prong adapter. The hotel I work at has really trashed power and you never know which room will hum when, so I carry one everywhere.


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