help me fix my powered sub humming problem :( - AVS Forum
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post #1 of 20 Old 06-09-2013, 09:16 PM - Thread Starter
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I have an HTIB JVC THD50 home theater system and it has served me well over the years.

My neighbor came by today and told me his friend was selling a his energy exl-s10 powered sub. He was asking a 100 for it. My neighbor let me borrow it for a test drive and it sounds and looks great. The surrounds are intact and the box itself isn't dinged up. The ONLY issue I noticed is a hum. If I turn the volume knob on the back up, the hum comes out of the speaker. But it sounds like there might be a hum coming from the amplifier(or power supply?) as well.

Since my jvc amp lacks low level sub outputs. I am using the two high-level outputs(it provides the signal and power for the stock sub) from the amp to feed the high-level inputs on the subs amplifier. The jvc amp has two outputs while the sub has 4 inputs. I used speaker wire and made a y-split for both + and - so I could feed both channels. I am not sure if this is "improper" but it seems to work fine. I am just worried about the hum. Any ideas?

Ingore my posts below unless you want to see countless troubleshooting steps. Skip to my final reply for the solution I came up with.
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post #2 of 20 Old 06-09-2013, 10:32 PM - Thread Starter
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I did some troubleshooting and these steps I found online have not fixed it.

1.If the subwoofer is plugged into its own outlet, plug the subwoofer's power cord into an outlet shared by the other components. Use an extension cord if necessary.
2.If the hum persists, and your system includes a cable TV, disconnect the cable line. If the hum stops, install an isolation transformer on the cable.
3.If the hum persists, disconnect the remaining component cables one at a time until the hum stops.

I noticed that even with all my AV equipment unplugged except for the subwoofer, it makes the noise. But if I unplug the high level inputs, the noise stops. The noise is definitely related to my amp. I am thinking I need a ground loop isolator on the highlevels?
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post #3 of 20 Old 06-10-2013, 03:09 PM - Thread Starter
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Anyone?

I did a little more testing and it is for sure related to my connection with the jvc amp. It doesn't make the noise when I unplug my high level leads. It does however make the noise, with the leads plugged in, regardless as to whether my entire audio/video system is plugged into the wall or not.

I am thinking a ground loop isolator is my only option? I am not replacing the amp.

My jvc amp does not have any subwoofer out rca ports to carry the signal to the sub. The sub that it came with was not powered, and therefore the speaker leads carry both the signal and the power. The specifications claim it puts out 200rms at 3 ohms(highly doubtful) on that lead. I am using this lead and I made a y-splitter out of speaker cable as the back of the energy sub has an input for left and right channel + and -. I believe this was meant to be daisy chained off my main speakers. But since my amp has a dedicated sub channel, I am using those instead.

I don't think there is any other option for me other than maybe trying a lineout converter to convert high-level to low level and use the rca port on the back of the sub, but I believe that port is meant only for the signal(not signal and power?). I would be afraid that this might burn out the amp? Or maybe a high level ground loop isolator to highlevel/low level?

I dunno you guys. Can anyone set me straight on what my options are? I like the sub, I think the price is right. I just want to integrate it into my htib system.
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post #4 of 20 Old 06-10-2013, 03:52 PM
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I'm not entirely sure the high level inputs are designed to take a powered signal without also outputting it to a set of speakers?

Normally you would connect the left and right front speaker outputs on the amp to the sub via the high level inputs. The you would connect your front left and right speakers to the high level output on the sub. The sub would then take over the low frequencies from the mains.

First try connecting the sub directly to the source signal via a short length of rca signal cable, bypassing the amp.
Then if there's no hum you can try using the high levels inputs as I described above.

If there's no hum after that you'll want to look into a reciever with subwoofer pre-amp outputs.
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post #5 of 20 Old 06-10-2013, 08:35 PM - Thread Starter
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Quote:
Originally Posted by Mik James View Post

I'm not entirely sure the high level inputs are designed to take a powered signal without also outputting it to a set of speakers?

Normally you would connect the left and right front speaker outputs on the amp to the sub via the high level inputs. The you would connect your front left and right speakers to the high level output on the sub. The sub would then take over the low frequencies from the mains.

First try connecting the sub directly to the source signal via a short length of rca signal cable, bypassing the amp.
Then if there's no hum you can try using the high levels inputs as I described above.

If there's no hum after that you'll want to look into a reciever with subwoofer pre-amp outputs.

Thanks for the reply. Yes, mine does not have any outputs. Only two sets of R/L + - inputs. The only way would be to daisy chain the speakers, or do my method of just plugging my sub channel speaker wires into it.

What would you suggest I hook the sub up to? I am not sure what I would use to by pass the amp.

Here is a link to the manual for it. The linked page shows what I am talking about.

http://www.manualslib.com/manual/47615/Energy-E-Xl-S10.html?page=20#manual
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post #6 of 20 Old 06-11-2013, 06:23 AM
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Ground loop noise is caused by having more than one ground path between devices.
http://www.rane.com/note110.html

In your case try disconnecting one or both of the speaker negative leads to the sub amp.

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post #7 of 20 Old 06-11-2013, 07:24 AM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Ground loop noise is caused by having more than one ground path between devices.
http://www.rane.com/note110.html

In your case try disconnecting one or both of the speaker negative leads to the sub amp.

I read the link after work. I tried disconnecting the leads one at a time. Still hummed with no negs disconnected. It still hummed with just one positive lead. Only stopped once all the leads were removed.
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post #8 of 20 Old 06-11-2013, 09:23 AM
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Quote:
Originally Posted by timaishu View Post

I read the link after work. I tried disconnecting the leads one at a time. Still hummed with no negs disconnected. It still hummed with just one positive lead. Only stopped once all the leads were removed.
Eliminate any other possibilities. Start by unplugging the TV cable, which is a notorious source of ground looping. If that doesn't work go to square one, unplug everything from the receiver except the sub. If it still hums you probably have a sub and receiver that just aren't going to work together. If it doesn't hum start adding connections. When adding one causes the hum to return you've found the problem.

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post #9 of 20 Old 06-11-2013, 09:55 AM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Eliminate any other possibilities. Start by unplugging the TV cable, which is a notorious source of ground looping. If that doesn't work go to square one, unplug everything from the receiver except the sub. If it still hums you probably have a sub and receiver that just aren't going to work together. If it doesn't hum start adding connections. When adding one causes the hum to return you've found the problem.

Yeah, its not my tv box/cable, already tried that yesterday. I have already tried unplugging all the power cords aside from the sub. I have also tried plugging it into the same power strip.. I will try unplugging everything from the back of amp and to see what happens. I will do that after work.
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post #10 of 20 Old 06-11-2013, 02:51 PM - Thread Starter
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Okay, so all I have hooked up to the back are my two rca cables that go to the tv. I unplugged that and it made no difference. I put my ear close, and with nothing hooked up to the sub, there is a humming sound coming from the amp/power supply. This humming happens with the jvc amp on or off; however, the humming from the woofer only happens when the amp is off. When I turn the amp off, the sub stops humming.

I am thinking at this point I should turn down the deal.
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post #11 of 20 Old 06-12-2013, 10:39 PM - Thread Starter
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I apologize for constantly bumping this.

I decided to put my ear to the sub box and I could hear a definite "humming" sound coming from within. It reminds me of that noise power lines make after it rains. A constant electrical hum.

This is the final bit of information. Power up, but with no high level leads plugged in, the amp humms (ear on sub box), if I max out the sub volume knob on the amp, I hear a little noise coming from the woofer(not all that much). Once I have a lead plugged in, the amp noise remains, but I now have a louder tone played through the woofer. It is quite loud if I max out the volume knob.

The strange part is the woofer is silent as long as my amplifier is turned on(even with no audio signal being played through it -tv off for example). The second I turn off my amp, the woofer becomes noisy.

Unless anyone can provide a solution. When I next see my neighbor, I am going to give it back. I really like the sub as its plenty of output for me and the price is right for me.
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post #12 of 20 Old 06-13-2013, 05:23 AM
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Quote:
Originally Posted by timaishu View Post

I decided to put my ear to the sub box and I could hear a definite "humming" sound coming from within. It reminds me of that noise power lines make after it rains. A constant electrical hum.
That's usually power transformer windings 'singing'. It's a symptom of an inexpensive amp, which may also explain the rest of the noise issues.

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post #13 of 20 Old 06-15-2013, 07:44 PM - Thread Starter
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Okay, new revelation.

I think any normal person would have given up by now, but being the curious person I am, I find it hard to stop troubleshooting. Anyways..

I took one of my car audio scosche line out converters (rated at 50rms), and took the high level (carries sub signal+power) wires and fed them into the loc, then took an rca cable, and used a 2-1 y-splitter and plugged that into the RCA sub input port, thereby negating the need to use the high level inputs on the sub.

Whataya know, doing so fixed the problem. No humming with my JVC amp turned off. Also when its off, messing with the sub volume knob makes no difference either. Out of curiosity, I put my fluke mutli-meter on the high-level leads, when off, my amp is not putting out any power on the sub channel(so that falsifies my idea that maybe it outputs a strange signal when off).

I know I cannot continue with my idea above however as it would destroy the amp.

Surely this has to be just a grounding issue. I just don't understand though why.
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post #14 of 20 Old 06-16-2013, 06:17 AM
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Since the issue is related to using the high level inputs direct from the receiver there's an incompatibility issue there, and likely the only way to fix it is with transformer isolation.

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post #15 of 20 Old 06-16-2013, 08:34 AM - Thread Starter
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Yes, I was reading about transformer isolation. I am believe this is the only solution at this point. They don't look exactly cheap either. Anyways, I am for sure going to give the sub back now that I discovered a solution; I would rather just wait until I get a receiver with a sub input out and try again at a later time.

Thanks again for your help.
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post #16 of 20 Old 06-18-2013, 05:55 PM
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Bill Whitlock has a recent PowerPoint with added notes paper. Start at page 99.

An Overview of Audio System Grounding and Interfacing
by
Bill Whitlock, President
Jensen Transformers, Inc.
Life Fellow, Audio Engineering Society

http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

Kevin
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post #17 of 20 Old 06-20-2013, 06:19 PM
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Use a cheater plug on the sub.

Klipsch RF 7 based HT 7.4, Pioneer SC 35, Acurus Five 200 amp, Chase SS 18.2(2), VS 18.1(2), Samsung BDP F 7500, Asus/My Book Live HPC 4 TB

Yaquin VK 2100 amp, McIntosh XR 5 speakers, Samsung BDP F 7500
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post #18 of 20 Old 06-20-2013, 07:22 PM
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Quote:
Originally Posted by derrickdj1 View Post

Use a cheater plug on the sub.
Advising someone to defeat electrical safety measures is irresponsible and stupid.

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post #19 of 20 Old 06-21-2013, 01:02 PM - Thread Starter
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A cheater plug would be useless because my sub already only as two prongs.

Also, I already gave the sub back. I decided to put the money towards something else instead.

Thanks anyways for your help everyone.
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post #20 of 20 Old 06-21-2013, 04:57 PM
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No argument with the advice from Bill.smile.gif

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