[mcallister]

I recently moved into a new home. I have an active 7 channel HT system using 6 subwoofers. 2 of the amps for my subs require a 30 amp outlet. I have had the system setup for a few months and everything was working great, no hum, some dsp hiss but otherwise all was good.

I had an electrician out last week to add two dedicated 30 amp lines so I could get the subs running, and while he was there I had him add a dedicated 20 amp line.

Upon turning everything on a horrible hum emanated from all the speakers. My first thought was it was my cable tv which I've had issues with in the past at different homes and that was not the culprit. I've now tried everything I can, have searched multiple threads on multiple websites and no luck.

I'm starting to think its within the panel. Tap you can hear a hum at the panel where the breakers were installed. However when I turn the breakers off the hum is still in the speakers. I've tried unplugging the amps, turning off the breakers that were added and hooking everything up the way it was before the lines were added and still the hum. I dissasembled the whole system and started plugging everything in on by one. As soon as my pre/pro gets any type of signal be it from my CD player, cable box, etc the hum starts.

Does this sound like a ground loop even . Does it sound like its from the breakers? The electrician doesn't think it is since when I turn them off the hum is still there.

Thanks for any help.

[mcallister]

Another thing to add I also tried an ebtech hum x that a fried had in his system that fixed a ground loop in his setup when he added a new pre/pro last year. It did nothing for mine. I added it at the pre/pro, at the conditioner plugged into everything, and even on one of the surround powered speakers and it did nothing.

I've also tried a cheater plug and it did nothing.

[Big Red Machine]

You have a hum in your panel?  Get that electrician back.  There should be no noise emanating from a residential panel.

[mcallister]

Maybe I'm just hearing things, I just checked the panel and I don't hear the hum there now. I swear it was there though when I was troubleshooting everything.

[ohenry]

I'd get an outlet tester at your local home store as a first step.  By simply plugging it in and reading the leds, you'll quickly determine if the grounds are properly wired, and if the neutrals and lines were switched.  The device doesn't cost much and it's a good idea to check all the outlets in your house anyway.

[liddown]

I am not claiming to be an expert in any fashion... However when I installed my dedicated lines in my house, I was advised to make sure that each new circuit was on the same phase within the panel as your other outlets feeding your system... In most cases (with modern panels) that means using every other breaker slot in the box... If you cannot find a ground / line issue, that might be something to have you electrician try....   

[dBe]

Mike, I'm pretty sure that if he added 2-30A and a 20a that he did it on opposite branch legs of the panel to balance the load on the incoming service.  Doing so will induce a ground hum when you connect all of this through your pre/processor because it will then see the different ground potentials from both branches of the service.

Bummer.

In order to minimize all of this, a separate subpanel containing all of the dedicated lines should be run so that grounding potentials are all the same.

Make sense?

Dave

[Speedskater]

Although 'Dave'(dBe) covered most of the territory, a few random thoughts:

a] Two 30A and one 20A for an A/V system?  Wow that's almost 10,000 Watts!
b] As above, when doing big power systems, it's best to bring one heavy run to a central point and install a breaker box there. The idea is to reduce the length of power cable from unit to unit.
c] With two extremely large power amps a 240V(120/120) Multi-Wire Branch circuit can be a good idea. (better with balanced inputs)
d] What sub-amps require a 30A circuit and how do you connect them to the receptacle's?

Now the important stuff:
There is a good chance that one or more of the circuits is mis-wired:
a] Get on of those 3 light testers.  Although I don't know how to connect it to a 30A receptacle, if you make an adapter it could also be mis-wired.
b] Read this article and get a non-contact voltage probe.
   http://ecmweb.com/contractor/failures-outlet-testing-exposed

[mcallister]

Thanks for the help guys. Here are some pics of the install. Tried more scenarios yesterday with no luck. Comments.....

[Ericus Rex]

Mike, I'm pretty sure that if he added 2-30A and a 20a that he did it on opposite branch legs of the panel to balance the load on the incoming service.  Doing so will induce a ground hum when you connect all of this through your pre/processor because it will then see the different ground potentials from both branches of the service.

Bummer.

In order to minimize all of this, a separate subpanel containing all of the dedicated lines should be run so that grounding potentials are all the same.

Make sense?

Dave

It would seem the simple test of this would be to plug all components into the same outlet and see if the hum goes away.  Use a power strip and extension cords to the subs if needed. Though I'm not exactly sure how you'll do that with those bizarre outlets....

Good luck!

[dBe]

Mike,

Next thing to try is disconnecting EVERYTHING that connects satellite or cable to the pre.  TV guys will put a ground anywhere and can create some huge grounding issues.  If this proves to be the source get a ground lift balun transformer at Target or one of the big box stores.

Let us know.

Dave

[mcallister]

I wanted to try that also but I'm not sure how to plug those 30 amp plugs into a power strip maybe some type of converter? However even with the 30 amp breakers shutoff the hum is still there  it's still there of the 20 amp outlet is shutoff also, and I hook everything up the way it was before we add the lines.

Dave the first thing I tried was uplugging the cable for the cable tv as I had that problem in my previous house and that's not the issue. I think what up you had mentioned before may be the problem. We are going to try adding another sub panel and a couple more dedicated 20 amp lines (surrounds are active) and see if that fixes it. I ready have 1 sub panel as is will that be okay to add a second?

[WGH]

As soon as my pre/pro gets any type of signal be it from my CD player, cable box, etc the hum starts.

Pre/pro broke? Replace it with a loaner.

Wayne

[dBe]

I wanted to try that also but I'm not sure how to plug those 30 amp plugs into a power strip maybe some type of converter? However even with the 30 amp breakers shutoff the hum is still there  it's still there of the 20 amp outlet is shutoff also, and I hook everything up the way it was before we add the lines.

Dave the first thing I tried was uplugging the cable for the cable tv as I had that problem in my previous house and that's not the issue. I think what up you had mentioned before may be the problem. We are going to try adding another sub panel and a couple more dedicated 20 amp lines (surrounds are active) and see if that fixes it. I ready have 1 sub panel as is will that be okay to add a second?

Yup, this one is a mystery, for sure.  I'll be interested in seeing the solution.  We all learn from each other.  It doesn't help your financial pain, but adds to the community knowledge base.

Dave

[mcallister]

 

Pre/pro broke? Replace it with a loaner.

Wayne

I have been thinking the same thing. Need to find a loaner I suppose.

[Bemopti123]

I have been thinking the same thing. Need to find a loaner I suppose.

Go to BBs, if you have one, get a HT receiver with some outputs and when and if you get try it and find out that it is the pre processor, you can return it. 

[kevin360]

However even with the 30 amp breakers shutoff the hum is still there  it's still there of the 20 amp outlet is shutoff also, and I hook everything up the way it was before we add the lines.

Remember, switching off a breaker does not disconnect the ground. If your problem is a ground loop, throwing breakers isn't going to help you isolate it. Do you still have the hum after unplugging the sub amps?

[ctviggen]

The easiest thing to do with all of these ground problems is to gut the system to a minimum system.  Unplug everything from the amplifier and only connect the amplifier to the power (and to the speakers). Turn on the amp.  Do you have hum?  If not turn off the amp, add the preamp into the system (with nothing connected to the preamp).  Turn on the preamp and amp. Do you have hum?  If not, keep adding one device until you find the source of the hum.

Using this, I determine a hum I had was caused by interconnects.  It took me a while to realize this.

[audiogoober]

The easiest thing to do with all of these ground problems is to gut the system to a minimum system.  Unplug everything from the amplifier and only connect the amplifier to the power (and to the speakers). Turn on the amp.  Do you have hum?  If not turn off the amp, add the preamp into the system (with nothing connected to the preamp).  Turn on the preamp and amp. Do you have hum?  If not, keep adding one device until you find the source of the hum.

Using this, I determine a hum I had was caused by interconnects.  It took me a while to realize this.

It may or may not be ground hum, but this is the best process for isolating the issue. +1 

[dBe]

The easiest thing to do with all of these ground problems is to gut the system to a minimum system.  T

Using this, I determine a hum I had was caused by interconnects.  It took me a while to realize this.

Good call.  I remembered a weird case involving interconnects.  Some interconnects have the shield disconnected at one end (telescoped).  Normal practice is to have the ground connected at the destination end.  In that instance turning one interconnect around fixed the hum.

Grounds be funny.

Dave