Yeah, yet another pro amp hum/ground loop question - AVS Forum
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post #1 of 22 Old 11-19-2012, 07:59 AM - Thread Starter
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All,

I have 2 pro amps powering my 2 lms-r 15" subs. I have a ground loop hum coming in from the source and I need to get rid of it.. In other words I do NOT hear the hum unless the source in plugged into my art cleanbox pro (see below).

I bought this at my local radio shack:

http://www.radioshack.com/product/index.jsp?productId=2062214

and while it works it makes lower frequencies in rew sound like wet farts. What is interesting is I tested Tron on bluray with the loop isolator in place and it didn't sound bad.. Just roomeq sounds nasty. I'm thinking if the signal is loud enough it gets past the isolator.

My current setup:

Denon 4311ci -> via RCA -> ART CLEANBoxPro -> via 2 xlr cables -> Crown xls 1500 AND EP4000.

What's funny is the CleanBoxPro doesn't clean anything.. it is simply a signal booster. If I unplug the RCA's from the CleanboxPro I do not hear the hum. Cheater plug won't work on the Denon (just for testing) as it is only a 2 prong plug. I'm looking for first hand suggestions at this point. Yes I've read a bunch of other threads/forums for suggestions.. This is in my basement so not only do I have a dimmer switch I also probably have a water heater and other things causing interference.

questions:
1) If I ran a new circuit from my breaker box would this help? Only for the amps
2) Any other options other than the crappy isolator from Radio Shack? I'm reaaaally thinking I might avoid this route.. I'm thinking even a 60+ dollar eliminator will still remove something from the source that I wouldn't want it to.

And yes I have read the other threads and while I heard thousands of "try this and try that" I don't think I've ever seen a solid outcome of "oh yeah this fixed it". I SHOULD also mention that it is NOT THE CABLE TV BOX. I've unplugged anything related to the Cable tv box (power, coax, hdmi to my receiver) and the hum is still there!!!

thanks,
Mike
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post #2 of 22 Old 11-19-2012, 08:49 AM
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Give #17 a try here: http://www.rane.com/note110.html

I've got a 50' RCA running from my receiver to my Reckhorn B-2, and the Reckhorn is then connected to my RMX-1850HD in the manner described in the link. Works perfectly. Originally, I did have a ground loop issue.
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post #3 of 22 Old 11-19-2012, 09:01 AM - Thread Starter
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Thanks for the quick follow up..

I checked #17 and it looks like an rca to xlr cable (specifically wired no doubt).. I'm kind of using the CleanboxPro to handle this conversion for me as well as boost the signal around 10 db.. I'm not sure if I can in via RCA connectors and went out via RCA connectors on the cleanbox pro if I would still get the 10 db increase.. Looks like the Reckhorn B-2 is doing a similar thing as the Cleanbox Pro except the cleanbox pro doesn't have any EQ.. only a signal boost for everything. Also the cleanbox has both RCA and XLR in and out.. I was hoping this would have been the better way to handle this conversion but it doesn't appear so..

thanks,
Mike
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post #4 of 22 Old 11-19-2012, 09:07 AM
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is anything that is plugged into your receiver a three prong device?

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post #5 of 22 Old 11-19-2012, 09:33 AM - Thread Starter
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Right now I have 4 devices plugged in

1) xbox 360 via component video (rgb connection) and toslink for audio
2) cable box (verizon fios).. but I unplugged this already, no difference.. this is via hdmi
3) newer samsung bluray player via hdmi
4) media center PC.. just a cheap dell pc via hdmi
5) projector via hdmi for output signal

#1 has a special box (not sure if you are familiar with the xbox power adapters).. I think this could be considered a 3 prong. I haven't heard anyone ever mention xbox 360 as a ground loop hum. #2 I think is only a 2 prong. #3 I also think is only a 2 prong. 4) I believe this is 3 prong 5) I'm pretty sure this is 3 prong.

I can trying unplugging everything tonight.. Though I would need 1 for a source to test (guess I can switch between 2 to test). I don't think this will correct the problem but definitely can try..

Mike
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post #6 of 22 Old 11-19-2012, 09:40 AM
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"I can trying unplugging everything tonight.."

that is really the only way to know which one of those grounds is forming the "loop" if in fact it is a ground loop that is causing the noise. from what you are describing, it sure sounds like a ground loop.

i think hdmi has ground connections in there, so #4 and #5 might be a good place to look.

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post #7 of 22 Old 11-19-2012, 09:45 AM
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I had to use cheater plugs on my PS3, projector, and laptop power supply to eliminate my hum. Try unplugging everything and 1 by 1 testing each component to see if it introduces a hum.
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post #8 of 22 Old 11-19-2012, 10:52 AM
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Quote:
Originally Posted by haanjamin View Post

I had to use cheater plugs on my PS3, projector, and laptop power supply to eliminate my hum.
Recommending that others bypass safety protocols, not a good idea. OP, this explains why ground loops occur and how to safely fix them:
http://www.rane.com/note110.html

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post #9 of 22 Old 11-19-2012, 10:52 AM
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Quote:
Originally Posted by haanjamin View Post

I had to use cheater plugs on my PS3, projector, and laptop power supply to eliminate my hum. Try unplugging everything and 1 by 1 testing each component to see if it introduces a hum.

PC or Laptop is usually a very good source for a hum. And then there is your dimmer switch...Big no-no as well.
Quote:
1) If I ran a new circuit from my breaker box would this help? Only for the amps

It is worth a shot for sure, and probably not all that expensive to do. The additional benefits of having a dedicated circuit for your HT also outweigh any other options in my honest opinion. I am now up to 3 dedicated outlets, just in case smile.gif

What are the gains on your amp, cleanbox, and amp set to? A lot of times the groundloop can be handled a little better with a proper gain structure. I have used the cleanbox, along with countless other boxes and have ended up settling on a plain ole' rca-xlr cable and the behringer DCX should I need any boost, I also get countless other benefits from that too, but it isn't really even necessary.

(European models do not accept banana plugs.)

 

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post #10 of 22 Old 11-19-2012, 11:07 AM
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a cheater plug on devices such as a laptop with plastic power adapters is probably ok, as the output voltage is typically 12-20v, but other than that, bfm is right.

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post #11 of 22 Old 11-19-2012, 11:07 AM - Thread Starter
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Quote:
Originally Posted by beastaudio View Post

PC or Laptop is usually a very good source for a hum. And then there is your dimmer switch...Big no-no as well.
It is worth a shot for sure, and probably not all that expensive to do. The additional benefits of having a dedicated circuit for your HT also outweigh any other options in my honest opinion. I am now up to 3 dedicated outlets, just in case smile.gif
What are the gains on your amp, cleanbox, and amp set to? A lot of times the groundloop can be handled a little better with a proper gain structure. I have used the cleanbox, along with countless other boxes and have ended up settling on a plain ole' rca-xlr cable and the behringer DCX should I need any boost, I also get countless other benefits from that too, but it isn't really even necessary.

1) I need me my danged dimmer switch tho! smile.gif
2) I talked to a friend (sometimes easier to discuss in person) and I would have to get like 2 or 3 dedicated outlets as if you don't also plug all components into a "good" outlet you will still introduce ground noise.. So I would need enough power for receiver, components AND my amps..
3) You know.. when I initially tried this pro-amp solution out I couldn't get enough of a signal with an onkyo amp.. Now that I'm on the Denon 4311ci I still don't think I get enough signal. With the CleanboxPro I am able to keep the sub level to around 0 on the receiver.. but I have to still crank up the Signal on the cleanboxpro... I was thinking of ordering the 18" Dayton sub from PE... so if these would work I wouldn't mind ordering 4 of them:

http://www.parts-express.com/pe/showdetl.cfm?partnumber=240-428

Are they just as good as the normal cables, rca to xlr?

thanks,
Mike
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post #12 of 22 Old 11-19-2012, 11:24 AM
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I would actually recommend getting those over the conversion cables. I just found the conversion cables before I found those. More than likely a better option anyways. HOSA makes some as well.

(European models do not accept banana plugs.)

 

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post #13 of 22 Old 11-19-2012, 11:44 AM - Thread Starter
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Originally Posted by beastaudio View Post

I would actually recommend getting those over the conversion cables. I just found the conversion cables before I found those. More than likely a better option anyways. HOSA makes some as well.

Ok cool... I'll pick 2 up to test with then.. I think what I was suggesting is that while it may work and I just crank the output on the receiver to +10 on both subwoofer channels it wouldn't give me any headroom at all.. I'm worried that if I go RCA to XLR with no boost I'll be missing output (and from my testing it seems like that is the case, but I don't mind revisiting this if it works out for the best). I'm justing thinking the XLS 1500 amp is already pretty weak and could use the signal boost.

Do you know if you have added any signal boost on the behringer DCX already? Maybe that's the difference?

thanks,
Mike
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post #14 of 22 Old 11-19-2012, 06:00 PM - Thread Starter
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Ok, so I did some testing.. I get the noise from when I plug my projector in via hdmi, from the cable box via hdmi and from the PC via hdmi.. Didn't think noise like this would be passed via hdmi.. learn something new each day..

so I have 3 total devices that create the ground loop.. and the cable box doesn't need to be plugged in so I'm guessing I have a ground loop via the cable into the box...

Any recommendations on what I could do other than running a separate couple of circuits.. even then it might not be avoidable simply because they all connect via hdmi... I think that's where I thought it wasn't the cable box because I simply unplugged the hdmi settop box from the receiver and still heard the hum (well duh I didn't think I had to worry about other hdmi connected devices).

thanks,
Mike
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post #15 of 22 Old 11-19-2012, 06:55 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Recommending that others bypass safety protocols, not a good idea. OP, this explains why ground loops occur and how to safely fix them:
http://www.rane.com/note110.html

Should have clarified: I agree that it is not the proper fix... I'm not recommending it, simply stating what I did to fix my problem. I'm fine with that fix in my application as those devices are enclosed in all plastic. I wouldn't do it to something with a metal exterior.
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post #16 of 22 Old 11-19-2012, 07:08 PM
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Quote:
Originally Posted by mikeciccarelli View Post

Ok, so I did some testing.. I get the noise from when I plug my projector in via hdmi, from the cable box via hdmi and from the PC via hdmi.. Didn't think noise like this would be passed via hdmi..
You wouldn't think so, if the signal is digital, but where there's a ground connection a loop can arise. Have you tried disconnecting the shield at one end of the XLRs?

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post #17 of 22 Old 11-19-2012, 07:26 PM
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Had your exact issue and posted in a few threads to help others about it.

My PJ was on a separate circuit and caused the ground issues. We had to run another line from the sub power panel where everything else in the rack is wired. This tied everything into the same sub panel eliminating the issues with using pro amps. With mine the noise was easily detected because i'm using pro amps for the mains also.

Unplugging one cable at a time finds the culprit. You could also rewire your receiver to a 3-prong power cord but no guarantees it solves the issue when something is plugged into a completely different room circuit. smile.gif

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post #18 of 22 Old 11-19-2012, 07:29 PM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

You wouldn't think so, if the signal is digital, but where there's a ground connection a loop can arise. Have you tried disconnecting the shield at one end of the XLRs?

No.. My experience is limited and I'm guessing I would have to ruin a XLR cable? I'm ok with testing a cable tho if I know exactly what to do.. I had an old "cheater" plug I just wanted to test with and if I connect only the projector and bluray player I don't get the hum through the pro-amps..

thanks,
Mike
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post #19 of 22 Old 11-19-2012, 07:30 PM - Thread Starter
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Quote:
Originally Posted by autox320 View Post

Had your exact issue and posted in a few threads to help others about it.
My PJ was on a separate circuit and caused the ground issues. We had to run another line from the sub power panel where everything else in the rack is wired. This tied everything into the same sub panel eliminating the issues with using pro amps. With mine the noise was easily detected because i'm using pro amps for the mains also.
Unplugging one cable at a time finds the culprit. You could also rewire your receiver to a 3-prong power cord but no guarantees it solves the issue when something is plugged into a completely different room circuit. smile.gif

I'll have to test but I think if I do something stupid (just to test) and plug everything into the same sixway (and then plug another six way into that one) the problem still exists.. so everything would be on the same circuit... I will definitely have to test though.

thanks,
Mike
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post #20 of 22 Old 11-19-2012, 08:40 PM
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since the pc and the projector don't require a ton of amperage, something like this can fix #4 and #5.

you don't need two of them if you are under 6 amps.

http://www.ebtechaudio.com/humxdes.html

they have one with two receptacles, but i forget what it is called.

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post #21 of 22 Old 11-19-2012, 08:46 PM
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as for the cable box, there is an isolator that goes in-line before the box to break the ground to the outdoors.

something like this: http://www.amazon.com/Viewsonics-VSIS-EU-Cable-Ground-Isolator/dp/B0017I3K9M

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post #22 of 22 Old 11-20-2012, 07:20 AM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

since the pc and the projector don't require a ton of amperage, something like this can fix #4 and #5.
you don't need two of them if you are under 6 amps.
http://www.ebtechaudio.com/humxdes.html
they have one with two receptacles, but i forget what it is called.

Yeah I might get one of these for the PC and projector...

As an update I actually moved my 2 6-way outlet strips to the same receptacle and that actually seemed to help.. it was getting late so I couldn't really test it.. I think if I use half gain maximum on the CleanboxPro that seems to help as well.. If I crank up everything to test noise (without anything playing) I can still hear some noise but it isn't too bad.. I think I will invest in 2 plugs eventually.

I had my amps plugged into one of those receptacles that can reset.. not sure what those are called and it might be a cheap one... so I avoided that receptacle altogether for now.

Ultimately a quick rundown:
1) found 3 devices that were causing ground loop via hdmi
2) plugging in all devices into same receptacle seemed to calm the loop down quite a bit but will test more tonight
3) I would eventually like to get 2 of the humx devices (though they aren't exactly cheap for only 6 amps)
4) would also like to get a clean 20 amp circuit run for all my devices, including amps.. I might actually do this first since I also want to wire up house with generator too..

thanks,
Mike
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