[WGH]

Sometimes equipment wears out. I used my old NAD 7155 receiver as a loaner to friends, a backup, and now it powers the center channel speakers for movies. I was wondering if the wiring in my new house was screwed up because when I plugged in the NAD there was a 60 Hz hum that I could not get rid of. As it turned out the pre-amp section of the amp was producing the hum. I removed the pre-amp/amp jumpers and now use only the amp section and it is completely silent again.

By the way, the amp sections of these old NAD receivers are fantastic. The pre-amp was the weak link that held these receivers back from a reaching legendary status.

Wayne

[audiogoober]

By the way, the amp sections of these old NAD receivers are fantastic. The pre-amp was the weak link that held these receivers back from a reaching legendary status.

Wayne

+1. The NAD 7100 stayed with me for several years in my younger days...  I ended up bridging it with the 2100 amp and it was a great combo thru other preamps.

[mcallister]

So here is the latest.

A couple previous posters have mentioned some ideas, the hum is there when I unplug the sub amps as well as with the breakers turned off. Also I did unplug everything, the pre/pro is a integra dhc-80.2. The speakers are all active danley sh-100bs for the LCR and active SH-100s for the 4 surrounds. Using balanced canare star quad XLR cables for each speaker.

I had mentioned earlier when I sent the signal from a source the hum was there. I found out it dose not need a signal at all I had it in direct so the pre/pro wasn't sending a signal to the speaker I was testing until I received a signal. So anyhow the hum is there with nothing hooked up to the pre/pro at all except the speakers.

So here is what I tried next to see if it was a possible bad cable. The Oppo BDP-95 I use as my source has balanced outputs for 2 channel playback which I use when doing strictly 2 channel listening with the DAnleys. The Danleys being active I just run straight from the XLR out of the Oppo to the XLR input of the Danleys. I did this with every speaker all 7 and no hum everything is golden. Plug back into the integra, turn it on and hum.

I've tried a cheater plug, I've grabbed an extension cord and plugged it into a different room, I've tried the new dedicated 20 amp line, the line conditioner, the ond line I used and still the hum.

I'm baffled.

[mcallister]

I'm going to add another sub panel dedicated to only the lines in my home theater. Anything I should do specifically if doing this . Is a single phase or 3 phase panel better? Etc. I really know nothing about this stuff

[Speedskater]

'mcallister' what country are you in?
Not 1 in 1000 homes in North America have 3 phase power.
All residential audio equipment is single phase.

You can use a sub-panel or just a small (6 or less) breaker box.
Try to place it in a central location near your room.
You want to reduce the unit to unit length of the runs.

[Speedskater]

'mcallister' maybe your were thinking of a 240V (120/120) sub-panel.
Unless you have more than one very large power amp,  then a 120V panel is the way to go.

PS. An electrician would call it a 'panel board'.

[mcallister]

Sorry I was just looking at menards website at some and they had some listed as 3 phase and some listed as single phase.

[richidoo]

To find the problem you need to simplify your system and do a lot of testing, like you have been. You can't think of "your system" as one system. Because you have active speakers, you really have 5 systems and they all interact with each other through the house wiring and the IC grounds.

The first weapon you need in your arsenal is an understanding of what ground loop hum is. If you don't understand what you are hunting you can't beat it. Ground loop hum is caused by different voltages on the grounds, which is caused by different resistances in the grounds due to bad connections or poor ground circuit design. The voltage on your IC ground is 1mV and the voltage on your PC ground is 4mV. That 3mV voltage difference causes current to move through the resistance of the conductors. The hum is actually the AC signal of the small ground voltage. If all of your grounds for power and signal were all the same, then there would be no relative voltage between them and no current could flow. An ideal ground system will offer low impedance, low resistance circuit between the component and the earthing rod, and all the components and wiring will carry the same ground potential. But the physical realities of electricity and building methods means that the length of the wires and the quality of their connections can change the resistance that the ground system sees, and this different resistance between different ground legs makes the voltage different.

The ultimate reference ground for your system and the house is the earthing rod - 10 foot long copper rod that is outside your house, just below the utility meter. This earth rod is connected to the service panel with a large gage bonding cable to bring low impedance ground into the house. Then all outlets are connected to this single source of ground so that voltage differences between outlets and appliances is minimized. Bad connections along the way can degrade the quality of ground to individual outlets and appliances. Code only allows ONE earthing rod on the house electrical system.

Impedance is the AC version of resistance. For AC systems we are talking impedance. Hum is AC signal, so impedance. The impedance of a ground wire from an outlet to the service panel can be increased (more resistance) by a few things. Back stabber connections to the outlets, loose wire nuts, too many wires in a small wire nut, loose screws on outlet, shared circuit with other outlets, switches between your audio outlet and the service panel. All these things raise the impedance and compromise your ground quality. The hot and neutral conductivity is reduced also with bad connections, but that's another topic. One of the benefits of running dedicated circuits is that you have a straight shot from the outlet to your service panel, which will ensure the lowest possible impedance for your outlet grounds.

What can happen is that the new dedicated outlets have a lower ground impedance than another shared circuit with a loose wire and a couple wire nuts on the grounds. This extra resistance causes the voltage potential on those ground to be different, which causes current to flow across the resistance and make a hum signal. This is one kind of hum that is caused by different ground resistances between two or more outlets. The ground loop is entirely in the house wiring, and can be fixed by opening up the outlets and improving the connections.

Another type of ground loop can occur when ground potential is different between two different electronic components in your system, like preamp and amp. In this case, the components can be plugged into the same outlet, so they have the same ground voltage for power supply, but inside the components the grounding scheme adds resistance in some way, causing the current to flow between the components through the interconnect. In this case the problem is the same as before, bad connections, bad solder joint, loose nut on the chassis ground bolt, whatever, that causes one side to have a different ground voltage than the other.

Since your HT system is complex, I would venture to guess that the older house wiring has higher impedance than the newer dedicated outlets, and this ground potential is looping through the preamp which connects all the different grounds together through the interconnects. So the object of fixing a ground loop hum is to minimize the resistance of ALL of the utility wires going back to the service panel, and to ensure that the internal ground circuits in your electronics are also low impedance design and in good repair.

Start with one simple system. That is one active speaker, connected to the preamp by IC, and both plugged into the same outlet with no power strips, all contacts clean and tight. If you have hum still, then there is a problem with your preamp or the plate amp in the speakers. Contact the mfg. Since this is a new problem since the new wiring, lets assume that the prepro and amps are OK.

If you get a quiet system with pre and speaker plugged into the same outlet, then you verify that the preamp is OK. You should theoretically get the same quiet result from all of the other active speakers if you move the preamp around the room using the same outlet as the speaker under test.

Now start adding these separate systems together to look for loops. Make a stereo only system with 2 speakers and preamp, all on one outlet (use a good quality power strip,) no source connected. If no hum, then move one of those speakers to a different outlet. If hum returns then you have house wiring issues on that outlet you moved the amp to and you need to tighten up your wiring to reduce resistance in the house wiring of that outlet going back to the service panel. Or install more dedicated lines to each speaker.    There's probably only one other circuit to that room in addition to the new dedicated circuits so you should be able to troubleshoot the old circuit easily. Tighten all the screws on the outlets, make sure the wires are screwed down to the side screws, and not poked into the back holes of the outlets. Redo any wirenuts, using the correct size nuts and not stuffing too many wires in there, make sure the wirenutted wires are all clean and twist together cleanly. Check for switches, ceiling lamps, etc. that might be in the path from your audio outlet back to the panel. 

Use this 2 speaker setup as a tool to test the ground quality of all of the other outlets that you are using. Instead of adding more speakers to the preamp, keep it simple and just move the power cords around to the different outlets. If you have two outlets that work together quietly, then that is your testing reference. When a new outlets makes hum, then that new outlet has a problem. Note that if you fix an outlet on a shared system, other outlets on that circuit could still be bad, if they are "further away" from the service panel on the circuit. You can have more than one loose screw on a given circuit.  All the outlets on a shared circuit might be wired well, but something upstream like a switch could be giving you trouble.

Remember that if you add one bad ground connection to the system, then everything connected will hum, not just the device on the bad outlet. So you have to find the bad outlet and fix it, or run a new dedicated line to that outlet, or move the devices in the bad outlet over to known good outlets.

You have overkill with the 120V 30A outlets. I would turn those into 20A outlets and reduce the breakers to 20A breakers so you can use normal plugs. The good thing is that you have 30A wiring in the walls which will provide low impedance for ground and current.

It's definitely important as mentioned above to verify that the old and new circuits are wired correctly. Use a outlet tester for the 15-20A circuits and check the 30A circuits by opening them up and verifying the wire colors are connected to the right terminals on the outlet. Be careful when you are opening up the house wiring!

Sorry for the rambling length.

[ohenry]

mcallister, If I understand correctly, you live in a relatively new home and everything was fine until the electrician added one 20 amp and two 30 amp circuits.  Now the system hums, even with the three new circuits turned off at the breaker box.

I'd have the three new circuits examined at the box and receptacles by another person (especially if the electrician didn't get a permit and no inspection was done).  It isn't rocket surgery to determine if they are properly connected and that seems like a logical place to start. 

It would be a nasty coincidence if your preamp decided to malfunction upon the first start-up using the new circuits... but we sometimes win the abuse lottery. 

[EDS_]

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.

http://www.jensen-transformers.com/an/generic%20seminar.pdf

The paper linked has saved my butt twice.

[mcallister]

Thank you Richidoo! This will be of great help I didn't think to do it this way. I have now verified it is not the pre so it is a ground loop which makes me feel a bit better.

[Rusty Jefferson]

You seem to be ignoring comments made early on in your request for help about your new branch circuits being on different legs of your incoming service. Explain to your electrician you need all 3 circuits from 1 leg of your service. Ask him to install a sub panel just for these circuits. He'll probably tell you at that moment, he can't do it without rewiring your whole panel, and/or bringing another service feed into the house.

I recently worked on a project that required bringing in another 200 amp service feed just for 2 channel audio (quad amped) and home theater (2 dedicated rooms) at someones home. 80 amps (dedicated) to a home theater from a 200 amp service panel may not even be possible. Are all the self powered speakers on the 1-20 amp circuit with all the electronics?

[Speedskater]

..............................................
The ultimate reference ground for your system and the house is the earthing rod - 10 foot long copper rod that is outside your house, just below the utility meter. This earth rod is connected to the service panel with a large gage bonding cable to bring low impedance ground into the house. Then all outlets are connected to this single source of ground so that voltage differences between outlets and appliances is minimized. Bad connections along the way can degrade the quality of ground to individual outlets and appliances. Code only allows ONE earthing rod on the house electrical system.
....................................... .........

Sorry for the rambling length.

'richidoo' if you removed this paragraph, you would have a very nice post!

That rod in the dirt has nothing to do with audio quality!  It is installed only for safety during thunderstorms and power company high-voltage accidents (but no, it's not a lightning rod).  Mother Earth has noise and leakage currents, just ask a farmer about his cows & horses and the drinking trough.  Tests have been done with battery powered high quality mic & pre-amp systems, the noise went up when they attached a ground rod.

[mcallister]

You seem to be ignoring comments made early on in your request for help about your new branch circuits being on different legs of your incoming service. Explain to your electrician you need all 3 circuits from 1 leg of your service. Ask him to install a sub panel just for these circuits. He'll probably tell you at that moment, he can't do it without rewiring your whole panel, and/or bringing another service feed into the house.

I recently worked on a project that required bringing in another 200 amp service feed just for 2 channel audio (quad amped) and home theater (2 dedicated rooms) at someones home. 80 amps (dedicated) to a home theater from a 200 amp service panel may not even be possible. Are all the self powered speakers on the 1-20 amp circuit with all the electronics?

I'm confused what was I ignoring? The surround speakers are on a seperate circuit than the electronics and front LCR. However I've tried putting everything back on that circuit (which is what I had originally before I added the dedicated lines) and the loop is still there.

[jaywills]

You might consider checking your interconnects.  i had a hum problem in one channel that drove me crazy until I started swapping the interconnects to see if the hum followed.  A ground had (non-obviously) come loose at one of the connectors.  Fixed it and hum was gone.  Hope this helps.  Good luck.  Cordially,

[richidoo]

Thanks Speedskater. "Ultimate" doesn't mean good, but final. Earth is the closest reference to zero volts that we have. It does not need to be silent to fulfill the purpose of a ground, because we don't listen to the earth noise on the ground through our system, unless ground is poor quality, high impedance. If the grounding system is healthy then all outlet grounds are always at the same voltage, no matter what the noise, and potential between the circuits is minimized along with hum. The 3rd prong is only there to enable circuit breakers to work, so anything close to zero is good enough. All we are concerned with is making all grounds the same voltage at all times. To do this we lower the impedance of the ground system throughout, so earth can most easily sink voltage throughout the system. Or think of it as earth "driving" a 0V signal throughout the system from a low source impedance. Not technically correct since the voltage is theoretically zero, but it works, kinda like the plumbing/electricity analogy.

You are right that earthing rod does not in theory audibly effect audio quality, as long as there is no ground loop hum. It could be argued that lower impedance ground provides a lower impedance neutral which is reference to the hot leg making it slightly more efficient in delivering current. But that's another topic.

I used battery powered system for a while. It was very quiet for the most part, but still had some hum problems when mains powered components were used. I solved that by connecting the battery negative terminal to the faceplate screw of a wall outlet, which is earthed. My current mains powered amplifier is quieter than the battery amp was due to better design in many aspects. 

The "safety during thunderstorms" function of the earth rod is the same reason it prevents hum. It's low impedance sinks voltage to earth efficiently. The low impedance sinks the wiring in the house to earth voltage. When all grounds have the same voltage, no ground loop hum. When all grounds, neutrals, metal appliances and antennas are sunk to earth volts then high voltage streamers can't form to attract a lightning strike.

[Speedskater]

'richidoo' so much of the fine print in your post is just wrong.
The ground rod (GEC) in the dirt has nothing to do with the Safety Ground (EGC/PE) system in the house. From an audio system prospective the only part that counts is the (EGC/PE) system.  How the ground rod (GEC) is connected has NO impact on the audio system.

Leakage current, noise and interference to not flow into Mother Earth and disappear.

For text books on the subject see:
Ralph Morrison
Henry W. Ott

For text books on the subject (audio system specific) see:
Jim Brown
Bill Whitlock

[Quiet Earth]

Read this article and get a non-contact voltage probe.
   http://ecmweb.com/contractor/failures-outlet-testing-exposed

Thanks for sharing this article Speedskater. I didn't know about the bootleg jumper trick as an installation short cut. Good grief  . Is there a particular non-contact voltage probe that you would recommend to purchase, or do you think they are all about the same? They are certainly cheap enough as a must have tool for the toolbox.

Also, as I understand the article, the non-contact voltage probe would detect a reverse polarity bootleg jumper at the ground terminal because ground is now hot. But what about a correct polarity bootleg jumper? The ground and neutral would still both be close to zeroVAC, wouldn't they? So, should I just use a voltmeter to make sure I don't measure exactly zero volts across neutral and earth ground?

Thanks again for sharing.

[EDS_]

Thanks for sharing this article Speedskater. I didn't know about the bootleg jumper trick as an installation short cut. Good grief  . Is there a particular non-contact voltage probe that you would recommend to purchase, or do you think they are all about the same? They are certainly cheap enough as a must have tool for the toolbox.

Also, as I understand the article, the non-contact voltage probe would detect a reverse polarity bootleg jumper at the ground terminal because ground is now hot. But what about a correct polarity bootleg jumper? The ground and neutral would still both be close to zeroVAC, wouldn't they? So, should I just use a voltmeter to make sure I don't measure exactly zero volts across neutral and earth ground?

Thanks again for sharing.

I left my glasses at the office so I can't really read the article linked.  But I can read the term "bootleg" ground in your post.

Bootleg grounding is always an NEC violation and should always be fixed when found. 

[Quiet Earth]

Thanks EDS_.

Yes, I was asking about the best way to detect a correct polarity bootleg ground. The article made it clear how to detect a reverse polarity bootleg ground, but I wasn't sure about a regular bootleg ground. My AC voltmeter has poor resolution, so I may pick up a better one when I get the non contact probe voltmeter.

I thought some of the guys might have more to say about it.