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balanced electrical power


Dave Horne

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There was an article recently in SOS where the sound guy (a well known person whose name I forget) extolled the virtues of balanced power. I never knew balanced power existed, I always associated the word balanced with shielded stereo cable (mic cable usually) but never with electrical power.

 

I have since checked the prices for units that can supply 20 amps or so of balanced power and the price is around $1700 (if my memory serves me correctly).

 

According to the author of the article using balanced power will eliminate all your ground loop problems and give you a very low noise floor. I have no need for this as I don't have a recording studio (or have golden ears). Just thought I'd pass this on. I'm sure someone here has balanced power in their studio.

No guitarists were harmed during the making of this message.

 

In general, harmonic complexity is inversely proportional to the ratio between chording and non-chording instruments.

 

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Quite some time ago I played a gig in Nome, Alaska. The power quality was so bad that I was getting ghost sounds out of my M1, making it almost unusable.

 

This was a long gig, 12 weeks, and there was only one channel in the band house, when it worked. So I went to the local cable company to set up cable service. I mentioned that I was in the band at the Polaris Bar, and that I was having a problem with the power. The manager of the cable company went into the back and got a power conditioner that would output balanced power. He loaned it to me, free of charge.

 

I took it back to the club, connected it up, and my M1 never worked better than it did the next 8 weeks. If I could afford one, I'd use it for every gig.

"In the beginning, Adam had the blues, 'cause he was lonesome.

So God helped him and created woman.

 

Now everybody's got the blues."

 

Willie Dixon

 

 

 

 

 

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I'm skeptical about "balanced power", and for good reason.

 

I'm an EE and know residential power distribution systems. From what I read about "balanced power", the hot and neutral blades of the AC socket each have 60VAC whose sum gives you 120VAC.

 

That completely defeats the purpose of the neutral connection of power distribution and makes it extremely hazardous.

 

A standard system has 120VAC on the hot connection, and the neutral is ground referenced to the substation. The purpose of the neutral is to provide a safe current path for a catastrophic failure.

 

If you have your hand on a metal chassis (think microphone, mixer console, guitar, or keyboard) and you're standing on ground, you are vulnerable to electric shock if the AC "hot" wire were to break and come in contact with the chassis. The current flows through the metal chassis, through you, to ground. You're fried before that breaker trips, if at all.

 

The "neutral" is designed to protect you from that hazard. "Neutral" is connected to any metal frame of any electrical appliance. Therefore if the AC "hot" wire were to touch the chassis, the current flows neutral (not through you) and the breaker trips. That is why neutral is at zero volts, it is a safety mechanism.

 

"Balanced power" now puts the "neutral" - and any metal chassis you come in contact with - at 60VAC with a real vulnerability to electric shock.

 

Also the "neutral" line is never fused in ANY residential wiring or appliance. If the "hot" side blows a breaker or fuse, a "balanced power" will still present an unfused 60VAC on the neutral side - a VERY dangerous situation.

 

The service from the utility pole to your breaker box is "balanced" with neutral - two 120VAC "hot" lines out of phase, which measure 240VAC. Either "hot" line measures 120VAC with respect to the neutral. This is a safe system that has been established since the 1930s.

 

The "balanced power" is NOT safe in that the safety feature of the neutral is completely defeated. And if you try to connect together gear from different power systems - watch the sparks fly!

 

Caveat Emptor on the FAQs of "balanced power". While they say as long as your gear is UL listed, it is safe to use on "balanced power" - but note that they neglect to claim UL approval for their power systems. BIG DIFFERENCE!

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I am also skeptical...

 

I'm an EE, but not an expert in power, so I am willing to be convinced otherwise, but...

 

While I see some possible advantages:

 

1) the furthest from ground either leg would be is 60 volts rather than 120, so the shock you could get would be considerably less than the 120V you would get with a conventional (US) setup. Since the power delivered varies as the square of the voltage, this would mean only 1/4 the energy in the shock. OK

 

2) Something would need to transform each leg from 120V down to 60V - if this were some sort of active circuit rather than just a transformer, it could reduce the noise that was otherwise on the two legs. This isn't a function of the balanced power, per se, but it might be fairly easy to do with the two lines - it is generally easier to reduce a voltage (ie. from 120 down to 60 in each leg) than it is to increase it.

 

However, I see even more disadvantages. As TRMC says, both legs would have a potential different from ground. I'm not quite as concerned of the shock hazard, because of 1) above, but it still doesn't seem very safe to me. I would want GFCI (i.e., fast acting) breakers, and on both legs, rather than just one. Theoretically, the protective ground (the "third prong," or green wire) is supposed to be isolated from the hot side, but here we have two "hot sides" - each 60V different from (protective) ground. I'm not sure I'd want to bet very much that all equipment is designed with both sides isolated from the protective ground. But given that they are, the protective ground should be connected to all exposed metal surfaces, so if either side makes accidental contact with this metal, the breaker should trip and protect anyone contacting the metal. It "should" be, but whether it is, I'm not sure I'd want to trust anyone on that!

 

A final problem seems to be the unconventional nature of it all. In addition to the concerns that things are wired properly, as stated above, such a unit would require that it be hooked up to both legs of the power system in the building, something that could be done at the breaker panel, but difficult to do anywhere else. Similarly, both legs would need to be protected by a circuit breaker, something that is a NO-NO in a conventional hookup.

 

The "balanced" part doesn't seem to be the thing that provides the noise reduction - unlike a balanced audio signal, where the idea is that any noise induced in a cable is common to both sides and therefore cancels out when amplified by a differential amplifier, here the noise would seem to be present on only one leg (whichever leg the motor, or whatever the noise source is), or, even if on both legs, would not act like a common mode voltage. If there is noise reduction, I think it is probably in the circuit used to reduce the voltage on each leg, as stated before, rather than an inherent characteristic of balanced power. A similar effect could probably be derived by using similar noise reduction circuits on regular single-phase unbalanced power.

 

If balanced power is such a good idea, why isn't it used more often? I would guess that the unit that provides the balanced power is fairly expensive. At similar cost one could buy a "conventional" power conditioning unit that would perform the same amount of noise reduction on an unbalanced line, with the added advantage that a connection to both legs of the electrical feed would not be necessary.

 

Maybe I am missing something - I am open to someone else convincing me otherwise. :wave:

 

- Bob

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The easiest way to get balanced power is with a center tapped 1:1 transformer.

 

The wire that should be providing safety, as well as a rough signal reference level, is the earth wire not the neutral. These should not be connected in the appliance, only at the entry to the house.

 

However if you have a piece of gear in which they are connected and you put this on a balanced power system, you are going to be in trouble. You've now got 60V on your cases relative to your house ground.

 

As for 60V not being dangerous - its less dangerous for sure but its current that kills, not voltage. All you have to do is get yourself a good enough connection.

 

There's a common myth that the neutral and earth are interchangeable so you will sometimes find them swapped in incorrectly wired plugs. On a balanced power system this is also quite bad.

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Center tapped 1:1 transformer is exactly what Furman is describing in their data sheet. They further state:

 

"Balanced power is recognized by the National Electrical Code (Article 530) for technical power applications. Its use is restricted to electronic equipment only. Balanced power may not be used for lighting equipment, and access must be restricted to use by qualified personnel only."

 

I would have to examine the NEC article to see what they say about circuit open and short fault handling.

Moe

---

 

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The NEC article addresses my concerns about short circuits and ground hazards.

 

Yes I am aware of the myth that earth and neutral are interchangeable - they are not. I was careful not to mix the two terms.

 

Yes current kills, but remember that current comes from voltage. With 60VAC on the neutral, there is a real danger of electricution.

 

A GFCI protects from ground/neutral faults, but will not work in a balanced power system.

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Can I assume in my situation (to remove a ground loop) where I have lifted the ground on everything in my rack case except on the amp (and also that the casing of every piece of equipment has continuity with ground) that a GFI device will protect me in a catastrophic failure? I do not use a balanced power set up.

No guitarists were harmed during the making of this message.

 

In general, harmonic complexity is inversely proportional to the ratio between chording and non-chording instruments.

 

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Originally posted by Dave Horne:

Can I assume in my situation (to remove a ground loop) where I have lifted the ground on everything in my rack case except on the amp (and also that the casing of every piece of equipment has continuity with ground) that a GFI device will protect me in a catastrophic failure? I do not use a balanced power set up.

Yes, a GFI will work.
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Thanks for the reply. I also thought I was covered but an editor from SOS called me an idiot in so many words.

 

The 'audio guy' who wrote that article in the Sept 06 issue of SOS was Roger Nichols. He created quite a stir with that article. There was a follow up in the Nov issue.

No guitarists were harmed during the making of this message.

 

In general, harmonic complexity is inversely proportional to the ratio between chording and non-chording instruments.

 

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I own an Equitech ET2R balanced AC transformer and boy is it heavy (and expensive)!

Contrary to some claims, balanced AC won't solve all your groundloop problems the minute you plug it in so it's not a magic bullet that will automatically get rid of your errant hum and buzzes. What such a unit can help you with is to better isolate potential problem sources (equipment with poor power supplies or grounding schemes etc.) of hum and buzzes, as it gives you somewhat of a starting reference point for your AC system from which you can track down equipment that are causing the buzzes or groundloops (at least that's been my experience). Once you've found a "dirty" piece of equipment, solving the problem is a whole other issue.

The other common claim that it will improve the sound of the equipment or widen the soundstage (and other pyscho acoustic things) is more difficult to discern. I guess some people will hear a difference and other won't but I don't feel the difference is very pronouced. After spending over $1k for an Equitech you better believe there's a difference! But it's like everything else: your audio system is only as good as its weakest link so in order to experience a substanstial improvement from using balanced AC you'd have to improve every other piece of equipment, cabling and monitoring(and also stuff like room acoustics etc). So for most, balanced AC should be the least of their worries.

Hope this helps.

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