Another electrical question

[MadFloyd]

My system has a dedicated 20 amp line for each monoblock. I also have a dedicated 20 amp line for my rack (sources, preamp).

I tried using single ended (RCA) cables from my preamp to my amp and noticed that I get a loud hum (ground issue) but this seems to be caused from the circuit that feeds the left channel; if I plug the left monoblock into the right amp circuit, there is no hum.

Can anyone explain why I get hum with one outlet/circuit and not the other? I'm wondering if my electrician did something wrong when I had him add the 2 dedicated circuits for my amps.

Thanks in advance.

 

[Fitzcaraldo215]

Likely, your line stage is at the same ground potential as the circuit for the right channel amp, but the left channel circuit is at a different ground potential. It is likely not a faulty ground on the left channel power circuit, although it might be. Possibly, an electrician could correct this at the breaker box by moving the breakers for left/right circuits to be in close proximity. Ideally, they should be on the same electrical "phase" and the same internal ground bus of the incoming two phase, higher voltage electrical power. That might be the problem and all that is necessary.

I also have separate 20A circuits for amps, subwoofers, other system components, etc. I specified that all power circuits be on the same phase. I had no problems until I also connected a PC on a different circuit in the next room. A noise/hum problem was cured by running a 3-prong plug extension cord to the PC from the same audio power circuit outlets. I use all balanced XLR interconnects, by the way.

I also had a problem in my old house with separate power circuits. The different circuits all came into the same ganged wall box, each to a separate duplex outlet. Not sure if it is legal or safe even, but I just ran a heavy bare copper wire among the ground tabs on all the duplex outlets inside the box. Problem solved.

 

[CGabriel]

My system has a dedicated 20 amp line for each monoblock. I also have a dedicated 20 amp line for my rack (sources, preamp).

I tried using single ended (RCA) cables from my preamp to my amp and noticed that I get a loud hum (ground issue) but this seems to be caused from the circuit that feeds the left channel; if I plug the left monoblock into the right amp circuit, there is no hum.

Can anyone explain why I get hum with one outlet/circuit and not the other? I'm wondering if my electrician did something wrong when I had him add the 2 dedicated circuits for my amps.

Thanks in advance.

Having more than one dedicated line has potential advantages in that there is more instantaneous current reserve available for the components. However, multiple lines can create a problem since there are also multiple paths to the ground in the electrical panel. Care must be taken when installing multiple dedicated lines regarding the impedance to ground for each of the lines. We always recommend that you make the physical length of the lines the same and use the same type and gauge of wire. Additionally, you may also use an AC analyzer to measure the impedance and voltage drop for each of the lines.

Differences in ground line or neutral line impedances between lines of more than a couple of tenths of an ohm can be a problem.

 

[MylesBAstor]

S

Likely, your line stage is at the same ground potential as the circuit for the right channel amp, but the left channel circuit is at a different ground potential. It is likely not a faulty ground on the left channel power circuit, although it might be. Possibly, an electrician could correct this at the breaker box by moving the breakers for left/right circuits to be in close proximity. Ideally, they should be on the same electrical "phase" and the same internal ground bus of the incoming two phase, higher voltage electrical power. That might be the problem and all that is necessary.

I also have separate 20A circuits for amps, subwoofers, other system components, etc. I specified that all power circuits be on the same phase. I had no problems until I also connected a PC on a different circuit in the next room. A noise/hum problem was cured by running a 3-prong plug extension cord to the PC from the same audio power circuit outlets. I use all balanced XLR interconnects, by the way.

I also had a problem in my old house with separate power circuits. The different circuits all came into the same ganged wall box, each to a separate duplex outlet. Not sure if it is legal or safe even, but I just ran a heavy bare copper wire among the ground tabs on all the duplex outlets inside the box. Problem solved.

That's missed quite often.

So is this and suggest getting one of the $9 outlet checkers to test that your outlets are wired correctly. When this electrician put in my dedicated lines, he totally misfired one outlet box.

http://www.amazon.com/GE-3-Wire-Rec...905&sr=8-1&keywords=electrical+outlet+checker

In fact, when he finished installing the lines and receptacles, I asked he was going to check if the receptacles were properly wired. All I got was a blank stare and that he had no way of checking. Went in my tool box, pulled out my $5 Sears Checker, told him to use it and voila, the electrician screwed up. Best of all he didn't want to fix it but I stood my ground and also didn't pay for the extra time this idiot had to take to retire the outlet box.

 

[Speedskater]

Those 3 LED outlet checkers can be easily fooled. Mike Sokol a pro-audio guy, has a much better test procedure.

"Failures in Outlet Testing Exposed"
Jul 15, 2013 Mike Sokol | Electrical Construction and Maintenance

http://ecmweb.com/contractor/failures-outlet-testing-exposed

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If I were to wire a room like this, I would run one large circuit (40 to 100 Amps) from the main breaker box to a small breaker box in/near the audio room. Then I would split it into individual 20A circuits.

 

[DaveC]

As SS said above, if you're going to run multiple lines it would be best to run one larger capacity line to a subpanel or breaker box that is located as close to your system as possible. This will minimize potential differences in your grounds. I think if you measure how much power your system actually uses you'll find multiple lines was overkill and unnecessary.

 

[MylesBAstor]

Those 3 LED outlet checkers can be easily fooled. Mike Sokol a pro-audio guy, has a much better test procedure.

"Failures in Outlet Testing Exposed"
Jul 15, 2013 Mike Sokol | Electrical Construction and Maintenance

http://ecmweb.com/contractor/failures-outlet-testing-exposed

***************************************
***************************************
If I were to wire a room like this, I would run one large circuit (40 to 100 Amps) from the main breaker box to a small breaker box in/near the audio room. Then I would split it into individual 20A circuits.

Thanks that was interesting. I might be wrong but that seems to mostly apply to pre-1965 building being converted due to electrical code changes. The tester should be applicable to Ian's case though.

 

[ddk]

Thanks that was interesting. I might be wrong but that seems to mostly apply to pre-1965 building being converted due to electrical code changes. The tester should be applicable to Ian's case though.

It depends Myles. I have the same tester and like it but I've seen it to be wrong on a number of occasions. One thing I learnt with ground loops is that there's no single surefire way to deal with them. At best all these simple gadgets and measuring techniques do is to alert you to a possible fault, finding and fixing it is whole other bowl of wax.

david

 

[garylkoh]

Actually...... there is a surefire way to deal with ground loops:

http://www.whatsbestforum.com/showthread.php?4248-RMAF-The-Interocitor-Saved-My-Life

I frequently run 230V in the back end (power amps, servo-bass amps) and 115V on the front amp (preamp, sources).

 

[garylkoh]

Oops - he no longer calls it the Interocitor. It's the Flex Connect

http://smcaudio.com/products/flex-connect/

 

[Speedskater]

It happens in new construction also! Audio Precision had it happen to them.

Audio.TST June 2013
Recently, AP celebrated the 15th anniversary of our custom designed building. Photo albums were displayed showing the construction and the move into our facility back in 1998. (My, how some people have changed in appearance!) Among my many memories of that time, I was reminded of a particularly nasty problem we experienced as we restarted operations in our new production environment.

Almost immediately after moving we began to experience failures of certain bench tests that are performed by our technicians during the course of product assembly and adjustment. After some research, we discovered our new building had some extremely large magnetic fields in the production area, almost as if it was haunted. These fields coupled high levels of hum into our products that were causing the test failures. AP products are designed to reject reasonable levels of stray magnetic fields that would typically be encountered in a lab or production environment. However the magnitude of the fields we faced were at least 20 dB worse.
We ultimately discovered that several of our AC outlets had been wired incorrectly, having their neutral and ground connections swapped. This is a big no-no from the safety viewpoint, but it also caused all of the neutral currents in a particular circuit (outside of our production area) to return through the safety ground connection and ultimately through plumbing and drainage pipes. Some of these plumbing pipes were located in the space directly above our production area while the main drainage pipe was buried directly below; thus our production area was effectively inside of a huge coil. Our electrical contractor was embarrassed but confirmed our diagnosis, and the problem was quickly fixed.
Sometimes one has to think “outside of the box” to correctly perceive or understand a given problem. In this case, our new building plans provided the necessary insight to recognize the inadvertent source of our unwanted magnetic fields (plumbing that formed a coil around our production area). Perhaps you might want to check the neutral and safety ground connections of the AC outlets in your own work space—there could be some ghosts present!

 

[ddk]

Actually...... there is a surefire way to deal with ground loops:

http://www.whatsbestforum.com/showthread.php?4248-RMAF-The-Interocitor-Saved-My-Life

I frequently run 230V in the back end (power amps, servo-bass amps) and 115V on the front amp (preamp, sources).

Isolation and balanced transformers don't always work for ground loops either Gary and they have sonic side effects, but I can see it under show conditions.

david

 

[ddk]

Oops - he no longer calls it the Interocitor. It's the Flex Connect

http://smcaudio.com/products/flex-connect/

First I thought that it was a joke because of the name and then I thought that you were talking about something serious above, not this! We use this type of inline with the signal transformers only in HT setups where the sonic penalty is immaterial. Plenty of them around, Jensen ISO-Max is one the best and costs quite a bit less than $2k if that's the actual price of Flex Connect. This isn't for Floyd and he has other options he can try.

http://www.jensen-transformers.com/home-theater/

david

PS. But you are right about signal line transformers being surefire, they're almost magical!

 

[garylkoh]

The cheapest solution - where sonic penalty is immaterial is the Rane Balance Buddy. That's something currently am using in my measurement systems to isolate the computer. I've also tried the Jensen, and other transformers and they are not transparent.

Steve's Flex Connect, on the other hand, IS transparent. On some systems, the impedance matching even makes the system sound better.

 

[MylesBAstor]

It happens in new construction also! Audio Precision had it happen to them.

Audio.TST June 2013
Recently, AP celebrated the 15th anniversary of our custom designed building. Photo albums were displayed showing the construction and the move into our facility back in 1998. (My, how some people have changed in appearance!) Among my many memories of that time, I was reminded of a particularly nasty problem we experienced as we restarted operations in our new production environment.

Almost immediately after moving we began to experience failures of certain bench tests that are performed by our technicians during the course of product assembly and adjustment. After some research, we discovered our new building had some extremely large magnetic fields in the production area, almost as if it was haunted. These fields coupled high levels of hum into our products that were causing the test failures. AP products are designed to reject reasonable levels of stray magnetic fields that would typically be encountered in a lab or production environment. However the magnitude of the fields we faced were at least 20 dB worse.
We ultimately discovered that several of our AC outlets had been wired incorrectly, having their neutral and ground connections swapped. This is a big no-no from the safety viewpoint, but it also caused all of the neutral currents in a particular circuit (outside of our production area) to return through the safety ground connection and ultimately through plumbing and drainage pipes. Some of these plumbing pipes were located in the space directly above our production area while the main drainage pipe was buried directly below; thus our production area was effectively inside of a huge coil. Our electrical contractor was embarrassed but confirmed our diagnosis, and the problem was quickly fixed.
Sometimes one has to think “outside of the box” to correctly perceive or understand a given problem. In this case, our new building plans provided the necessary insight to recognize the inadvertent source of our unwanted magnetic fields (plumbing that formed a coil around our production area). Perhaps you might want to check the neutral and safety ground connections of the AC outlets in your own work space—there could be some ghosts present!

But the receptacles still need to be checked.

Let me ask though. There's an issue obviously with false negatives but if the checker turns up a positive result, it should be correct? As in my case that definitely showed the outlets were miswired.

 

[Steve Williams]

But the receptacles still need to be checked.

Let me ask though. There's an issue obviously with false negatives but if the checker turns up a positive result, it should be correct? As in my case that definitely showed the outlets were miswired.

specificity vs sensitivity issues

 

[Speedskater]

Just today, I read about a complication to the "Failures in Outlet Testing Exposed" test. The newest NCVT probes are too sensitive.

The article author, now moderates a sub-forum on AC power and pro audio & lighting. While some of the threads are about generators or big 3 phase system, other threads are very interesting.

• AC Power and Grounding (Moderator: Mike Sokol)

http://forums.prosoundweb.com/index.php?board=82.0

Useless vs Useful NCVT
http://forums.prosoundweb.com/index.php/topic,154992.0.html

Porta-Potty Service Panel
http://forums.prosoundweb.com/index.php/topic,154772.0.html

 

[ddk]

The cheapest solution - where sonic penalty is immaterial is the Rane Balance Buddy. That's something currently am using in my measurement systems to isolate the computer. I've also tried the Jensen, and other transformers and they are not transparent.

Steve's Flex Connect, on the other hand, IS transparent. On some systems, the impedance matching even makes the system sound better.

This is a band-aid and it can't be transparent by definition. Its a transformer filtering the SIGNAL and messing with the ground connection, that's all. Does it do anything else? It doesn't fix the source of the problem, wether its mains or poor component design. Then you need two boxes and double runs of expensive interconnects $$$$$$ for the Audiophilia Nervosa. Jensen is one the best TRANSFORMER manufacturers in the industry, they're just not into the boutique pricing.

david

 

[ddk]

Let me ask though. There's an issue obviously with false negatives but if the checker turns up a positive result, it should be correct?

Not always.

david

 

[Speedskater]

A good electrician should have a meter ($300-$500) to do a complete test.

I think that Caelin Gabriel has one of those meters.