# Made system changes, now have ground loop hum?



## NickTF (Jul 3, 2007)

Guys, my system consists of 7 speakers powered by a pioneer 1015 Tx reciever, a QSC PLX 3602 pro amp which powered my DIY subwoofer system, and a velodyne sms1 to eq the sub. Now i've recently sold the diy sub to implement an infinite baffle system. In the mean time i've switched my QSC pro amp to powering my main speakers. Obviously the sms1 is out of the system for the time being. I've had cable ground loop problems in the past and eliminated those problems with a piece from parts express which goes between the cable outlet and the line. 

Now since i've switched the QSC amp to power the mains and removed the sms1 I now have ground loop hum again.

Any suggestions on things to check?

My system is and has always been powered by 3 separate 20 amp circuits that were wired just for my audio equipment during construction of my house (new construction). I did not change up anything and my reciever remains on one of the circuits, the QSC pro amp on another, and the remainder of my stuff on the third 20 amp circuit. 

Just to reitterate I was able to eliminate the ground loop problem before. What would cause it to return?


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## brucek (Apr 11, 2006)

> I was able to eliminate the ground loop problem before


What was causing it and what did you do to eliminate it before?

brucek


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## NickTF (Jul 3, 2007)

brucek said:


> What was causing it and what did you do to eliminate it before?
> 
> brucek


Well the 1st time I solved the ground loop hum I read here and on avs about the cable causing it so I started fulling around with it, unscrewing the cable connection, etc. and found out that was the problem. I purchased the cable ground loop hum eliminator from parts express which screws into the cable outlet and the cable screwing into it and it fixed the problem.

Now, it seems my ground loop hum (the same exact noise) has returned but I don't know what from considering the only change was moving the QSCPro amp to powering my mains instead of my now sold subwoofer.

Also, i've noticed that the system sense it's always been in my new construction house will sometimes cut sound for a second to a half of a second when appliances, lights, the hvac kicks on, and just anything in general is plugged in or turned on in my house. What would cause something like this?


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## brucek (Apr 11, 2006)

Are the three 20 amp circuits on the same leg of the service panel? If not, you shouldn't have the receiver and QSC amp on different legs.

You didn't say where the hum was coming from. Mains or IB?

brucek


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## NickTF (Jul 3, 2007)

brucek said:


> Are the three 20 amp circuits on the same leg of the service panel? If not, you shouldn't have the receiver and QSC amp on different legs.
> 
> You didn't say where the hum was coming from. Mains or IB?
> 
> brucek



There are no subs currently which is why my QSC amp is powering my mains. The hum is coming from all speakers. 

I did not run these circuits, the builder did. I know the Audio 1, Audio 2, and Audio 3 breakers are located in the top of my breaker box, that's about it. How would I go about finding out what you've asked?


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## brucek (Apr 11, 2006)

> How would I go about finding out what you've asked?


Unless you're comfortable with using a meter and sticking the leads in wall sockets, I won't bother telling you.

An easy method to ensure the QSC and receiver are on the same leg is to simply plug them into the same receptacle and see if the hum goes away. If it does, then that's the problem. If not, to ensure that it was indeed the addition of the QSC to the mix that is causing the hum, you could temporarily plug the QSC into a 'cheater' plug and see if the hum goes away. If not the problem lies elswhere. 

You could also try using a set of RCA to XLR cables with the shield lifted (between the receiver and QSC) to see if that clears the problem.

brucek


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## tonyvdb (Sep 5, 2007)

20 amps should be more than enough to power all your equipment on just the one circuit. If the breakers in the panel are all just in a row then they wont be on the same leg and that can cause issues. You say that your system pauses or stops playing music when the AC comes on? This can be several things, 
One it could be a loose connection in the panel usually the main lugs need tightening. 
Two it could be a floating or bad neutral or ground. Did you flip off the breakers one at a time to make sure that they are dedicated to the plugs for your system?
*NOTE: don't attempt to tighten the lugs or breaker screws in the panel yourself have a qualified electrition do this.*


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## NickTF (Jul 3, 2007)

In this thread or in another in another forum I was told to make sure that my cable box is plugged in on the same dedicated lines as the rest of my audio equipment. It turns out I had the cable box plugged into one of the non-dedicated sockets Well I have done so and have noticed that the sound no longer cuts in and out from time to time and the system does not seem to have the same amount of hum. I have only limited time (little bit of t.v. last night) with the change though so if it comes back i'll be sure to report.

P.s. at full power (as discussed with typical program material not sign wave testing) the qsc plx3602 pulls I think just over 20 amps, I can't remember. At full power sign wave it's something silly like 60 amps.

p.p.s. I just looked and it's 18 amps at 1/8th power pink (typical program material) noise and 63 amps at full power.


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## NickTF (Jul 3, 2007)

It turns out it had nothing to do with the cable box this time around. It seems when removing and plugging back in the rca connections to my pro amp the hum goes and then comes back (comes back once hooked up). I'm guessing this means a cheater plug is needed for my pro amp which will eliminate it's ground?


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## NickTF (Jul 3, 2007)

Cheater plug fixed the hum!


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## Wayne A. Pflughaupt (Apr 13, 2006)

It usually does, but it’s not the best approach. And it didn’t really fix the problem. 

I’m betting that it is still the cable box, or in the cable line. If the noise goes away when you unplug the coax from the wall, that’s your indicator. May sure your CATV service is grounded to the same ground stake that the service panel is. Even if it is, we’ve had people find that the connection had corroded, adding resistance, and hence a hum. When they disconnected everything and cleaned up all the connections, restoring good copper-to-copper connectivity, they problem went away.

Regards,
Wayne


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