[Wayner]

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.

Your amps came with 30 amp plugs? Why? I also wonder about the receptacle, as my reference book says its for recreational vehicles (TT-30R), and probably not meant for the use you are using it for. It perhaps should have been a NEMA 5-30R instead. These are industrial outlets anyway, and I'm confused why you would use industrial amps to power some home sub-woofers. The whole system seems to be very "iffy" in my books. Hopefully the electrician used some big ass wire for the 30 amp outlets. In most home settings, a 30 or 40 amp outlet would be for dryers and ranges, not stereo amps, and those same outlets would be 240 volt.

He didn't wire it for 240, did he?????

Wayner

[Folsom]

Checking phase would be smart. I will second ground thoughts; ask the electrician how the grounds to all three outlets are connected. Preferably they each would have their own individal wire going back to the same sub panel that has all av gear outlet on in, in same phase. Electricians don't care about that and will think it's a waste of time not required for code; too bad, it works better.

Speedskater you are flat out wrong about earth ground and noise. All high end studios not only have big ground rods, but they also have them in a special mixture that forms a cementish block that further drops impedence. The sole purpose is for noise reduction. Start studying inside electronics and you'll get why once code is met no one gives a rats ass about what its function should be, and rather what it is or is not doing for them.

[Wayner]

There is only one phase. Both lines of the 120 are on the same phase, or we would have an arc flash explosion. If you would like to call it a "split" phase, that would be OK, but that is where the buck stops.

240 volt is made from summing up 2 120 volt lines (that are both of the same phase).

Also, whoever said the grounding rod had nothing to do with the safety ground............

Wayner

[Speedskater]

Also, whoever said the grounding rod had nothing to do with the safety ground............

Wayner

Well what I said was:
The ground rod is part of the 'Grounding Electrode Conductor' (GEC) circuit.
The Safety Ground is the Equipment Grounding Conductor/Protective Earth (EGC/PE) circuit.
The only place that these two circuits (GEC)(EGC) can and must be joined together is at the service entrance/main circuit breaker box.
The Protective Earth (PE) has different rules.

The Safety Ground has one purpose, the ground rod has another.

[Wayner]

They work together to protect the system from unusual ground faults, and the likes of lightning effects. They are co-dependent on each other for a complete ground system. So to make a statement that it has "nothing to do" with the global grounding system is like saying that one of the legs of a three legged table isn't that important. If you don't think so, then go cut off the strap to your grounding rod.

If this thread is to be used as a "teaching tool" (my assumption), then it needs to be taken down to a more simple level, so all can understand the circuit terms and what they do, rather then rattle off a bunch of acronyms that are meaningless to almost all. Just a friendly suggestion.....

Wayner

[Folsom]

Service to a house contains two hot but out of phase with eachother and a neutral. You can screw it up. It won't necessarily cause sparks. But I don't think any licensed electrician would.

Wayner, thanks. You got it. Perhaps Speedskater is referencing when houses get ground with service; but I've never even see it. Where this is done? I dunno? New buildings, certain states? Images on Google search? I assume these places also have their own ground rod. But just to note the service ground is just a ground rod next to the service pole. Otherwise what are is speedskater going on about?

[andy_c]

What Speedskater is saying, and he is correct, is that a connection to earth through the grounding rod at the service entrance is not a requirement for low circuit noise, contrary to the claim of at least one person in this thread.  It's solely a safety feature.

[Folsom]

Yes that is the original intent, but for an audiophile it can do both. And aany true audiophile will seek what's better.

[andy_c]

There's subtle distinctions that need to be made.  It can definitely be a benefit to have the lowest impedance possible in the safety ground system (from third prong of outlets back to the junction box that feeds them).  That's due to unintended signal currents that can sneak into this path, especially in unbalanced systems.  Hum reduction is possible.

But from the earth ground rod to the safety ground of the service entrance, that path has no current at all in the absence of a lightning strike or similar catastrophic event.  Enhanced safety is possible through robust construction, but anyone arguing any potential sound quality improvement by altering that path isn't playing with a full deck.

[EDS_]

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.

OK good I feel better.

[Folsom]

But from the earth ground rod to the safety ground of the service entrance, that path has no current at all in the absence of a lightning strike or similar catastrophic event.  Enhanced safety is possible through robust construction, but anyone arguing any potential sound quality improvement by altering that path isn't playing with a full deck.

As far as noise is concerned that is only true if impedance is lower on the neutral coming into the service box, than the ground.

Hence why a very advanced grounding rod technique could offer lower impedance, and hence lower noise.

[andyr]

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.

Thanks for this tip, Speedskater.

I am planning the hifi circuits in a new house we are about to start building.  There will be 3-phase power into the building (to power aircon, a car-stacker and a lift, apart from the normal domestic stuff) and I am going to go "all-out" in terms of circuits for hifi!!    I was thinking of using 1 phase entirely for the music system - so I can have 10 or 11, 20a circuits, each ending in a dedicated wall socket.

I was thinking of having separate lines from the central power-box to the hifi area - so 10 or 11, 32a wires running 40'-50'.  However, I'm assuming your advice would be to run a single 80a wire to take 1 phase from the central to the hifi area ... and then have short individual 20a wires running from a breaker box to each wall socket (so the lines would be only 5-20' long?).    Am I correct?


Regards,

Andy

[Folsom]

Andy go with individual grounds from the Hi-fi sockets back to the hi-fi junction box. Don't daisy chain them. Like I said earlier, and electrician won't care, but an audiophile will.

[andyr]

Andy go with individual grounds from the Hi-fi sockets back to the hi-fi junction box. Don't daisy chain them. Like I said earlier, and electrician won't care, but an audiophile will.

Thanks, Salis - that's exactly what I am planning to do.

However, I'm interested in which is the better arrangement:

A.   1 x 80a wire from the main switch/meter box, where the power comes in off the street, to a breaker box in the hi fi room ... and then 11 (short) individual wires from this to the 11 wall sockets?
OR
B.  11 (long) wires from the main switch/meter box to the 11 wall sockets in the hi fi room?


Regards,

Andy

[Speedskater]

Choose "A"

One long heavy cable from the main breaker box to a big junction box at a central location in the listening room.  Then star out to the different outlet box locations.  Each outlet box (not each receptacle) should have one cable back to the big junction box.

Note:
You can have lots of receptacle's in one outlet box.
By cable I mean: 1 Hot, 1 Neutral & 1 Safety Ground.

Remember that we are trying to keep the length of AC power cable from component to component short.

[mcgsxr]

I did A.

I have a pony panel inside my media closet.  It has 8 breakers in it.  5 of them go about 3 feet to a single duplex outlet each.  The other 3 are for a future PJ,  drop down screen, and one that runs my 2 of my current Plasma's (so potentially not a dedicated circuit after all, since it actually has 2 outlets on that line, one in the basement and one upstairs).

Either way, it all works a treat, and should I ever desire 20A lines in the media closet, it will be a snap to drop 1 piece of drywall (the media closet was not mudded and taped since it lives behind a door) and pull those 5 outlets with associated wiring.

[andyr]

Thanks, guys.  A. it is! 


Andy

[Quiet Earth]

I can have 10 or 11, 20a circuits, each ending in a dedicated wall socket.

Why?

[andyr]

Why?

Why ... simples! 

When I did a big renovation on my house, about 6 years ago, I replaced a single, dedicated (spur) circuit for my hi-fi sources with 2 dedicated circuits - 1 for analogue sources and 1 for digital sources.  Power amps remained on a different circuit, up the other end of the room.

The improvement in sound from going to 2 source circuits was substantial!! 

Hence, for the new house which we are starting to build, I thought I would carry that concept to the extreme ... and have one dediated line per component.    The increase in cost for doing this will be neglegible, compared to the total build budget.


Regards,

Andy

[Quiet Earth]

Well, I thought it was kind of weird that you made that decision in a thread titled "terrible hum after adding dedicated lines". You know, like I get hum with the complexity of three AC circuits so I will add five more and make it better. 

I am probably the only one on Audio Circle who thinks less is more when it comes to dedicated AC lines.

About 10 years ago, I put two dedicated 15 amp lines in my listening room before I moved in. Back in those days I believed everything I read on the internet, so I knew that I had to have at least two lines. One for analog and one for digital. Or, one for source and one for power. No matter how much I tried I could only get good clean sound using one single line. Everything plugged into the same line sounded better and quieter. It's still what works best for me, even though the general internet wisdom proves otherwise. Maybe my situation is unusual. Maybe my system is too modest.

Wayner mentioned simplifying what we say and how we say it if this is to be a useful teaching thread. I say add up the amperage that you need for your audio system, and then provide a single dedicated line of that current capacity for the entire system. It all gets connected together anyway, so why not plug it into one single dedicated line?

Too easy?