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Author Topic: Balanced Power Questions  (Read 9506 times)

Mike Sokol

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Balanced Power Questions
« on: November 23, 2013, 08:58:24 pm »

Anybody here using balanced power in a studio? For those of you new to the concept, it uses a center-tapped, 120-volt isolation power transformer that provides 60 volts on the hot contacts of the receptacles with an inverted phase 60-volts on the neutral contacts. So measuring from H-N gives you 120-volts, but measuring H-G and N-G gives you just 60-volts. This is supposed to "balance" out any hum fields and provide better sounding recordings. Perhaps it also provides a few other advantages I haven't thought about. 

I've read about balanced power for years and only occasionally ran into it in a studio here and there, but the University I'm now teaching at weekly uses it in their SSL studio. Freaked me out the first time I measured the receptacle power for the students, but I quickly figured out the wiring once I saw the Furman balanced power units in the machine room.

So is this balanced power stuff snake oil or the real deal? I could actually test this for hum by dragging a guitar amp between a standard power studio and the balanced power studio while checking for speaker hum level using a calibrated mic. 

Any thoughts?

Mike Sokol
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Mike Sokol
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Cailen Waddell

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Re: Balanced Power Questions
« Reply #1 on: November 23, 2013, 10:30:39 pm »

Back in the day I remember loading in a couple tours that had giant rolling isolation transformers that I was told made balanced power. I also knew a local company that had one.  That's said that is the extent of my knowledge on the subject.  I too would be interested to hear more about it and applications where it was beneficial.
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Tim McCulloch

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Re: Balanced Power Questions
« Reply #2 on: November 23, 2013, 11:35:23 pm »

Mike, land-based balanced power was being touted 20-25 years ago, conveniently coinciding with the Epic Rise of the Pin One Issue.  Causal?  I'm not taking sides here ;)

The first time I read anything about b.p. it was kind of snake-oily without a whole lot of initial explanation about where the "power" Gremlins entered but somehow "balancing" the AC would rid the studio grid of them by not feeding them after midnight.  8)  Or somehow the AC got 6dB quieter.  Or there is a volcano, a virgin  and a full moon involved...

At any rate it looked expensive and inconvenient to use in live audio so I didn't give it much more thought.

Was the install in the Uni's studio pro-active or reactive to a specific problem?  SSL recommendation?  What does the studio staff think about it?
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Steve M Smith

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Re: Balanced Power Questions
« Reply #3 on: November 24, 2013, 05:56:07 am »

I mentioned this on another thread but will repeat it here:

In the UK, building site tools are powered by 110 volts, stepped down and isolated from our 240 volt supply by a transformer.  The centre point of the transformer is connected to ground.  This is for safety so that if there is a fault condition, the maximum potential to ground is only 55 volts.

I'm not sure if it would have any benefit for audio.


Steve.
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Mike Sokol

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Re: Balanced Power Questions
« Reply #4 on: November 24, 2013, 07:34:25 pm »

Was the install in the Uni's studio pro-active or reactive to a specific problem?  SSL recommendation?  What does the studio staff think about it?
I believe it was part of the original studio design which included the SSL console. However they did a few things with the install that was not so great. For instance, the SSL's power supply draws about 15 amps steady-state, and its machine room was fed from a sub-panel with around 250-ft of 12-gauge wire on a 20-amp receptacle. So there was a 12-volt drop from 118-volts in the sub-panel down to 106-volts at the power supply receptacle due to the 250-ft of run. I figured this out while troubleshooting the SSL for occasionally not booting up correctly (yup, lots of digital stuff) and when I told their tech support that the AC voltage was around 106 volts they kinda flipped out.

As luck would have it, I found an unused 30-amp twist-lock outlet in the machine room with a shorter run of 10-gauge from the same panel. So we changed out the cable feeding the rack for a 30-amp twist-lock (yup, we up-sized all the proper cables), and ended up with a solid 115-volts at the SSL supply, which made the console much more happy. Oh yes, there's a pair of really big Furman balanced power transformers, one for the console and one for the studio power. Because this was balanced power the studio tech assumed the console would run on the magical lower voltage, but that's not the case.

I'll do some more snooping around for grins, but I'm still thinking balanced power is an expensive gizmo that confuses technicians with no real benefits. But maybe I'm wrong.   
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Simon Lewis

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Re: Balanced Power Questions
« Reply #5 on: November 24, 2013, 07:41:56 pm »

There are some useful noise cancellation effects, but it also introduces a number of possible safety problems.

This reply to an article singing the praises of balanced power is useful reading...

http://www.soundonsound.com/sos/nov06/articles/crosstalk_1106.htm
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Geoff Doane

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Re: Balanced Power Questions
« Reply #6 on: November 24, 2013, 08:24:10 pm »

There are some useful noise cancellation effects, but it also introduces a number of possible safety problems.

This reply to an article singing the praises of balanced power is useful reading...

http://www.soundonsound.com/sos/nov06/articles/crosstalk_1106.htm

The reply talks about the safety aspects only.  Nothing really about WHY it's supposed to work.  Any of the reading I've done on the subject stipulated that double pole breakers and GFIs MUST be used in a balanced power distribution system, which should render it reasonably safe.

Although I have no practical experience with balanced power, the reading I've done on it's advantages seems to zero in on the line filters commonly found in guitar amplifiers.  The article made the claim that these filters were essentially balanced (inductor in series with line and neutral, and bypass caps to ground), and wouldn't pay nice with normal 120-0V power.  The claim was that a formerly noisy tube guitar amp, was so quiet with balanced power, that people wondered if it was actually on.

I look after a couple SSL installations, and SSL certainly doesn't require balanced power (or make any mention of it, that I can think of).  The only problem we had was that the two main PSUs  for the console shipped with main circuit breakers that were sized for 240V operation, not 120.  They were right on the edge, and would trip after an hour or so of operation.  Once that was spotted, and larger (20A?) breakers were installed, everything worked fine.  We did a proof of performance, and the installed console met or exceeded spec.  The PSUs don't have any special filtering on the line side, just the circuit breaker, fuse, and thermal switches on the heat sinks.

GTD
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John Roberts {JR}

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Re: Balanced Power Questions
« Reply #7 on: November 24, 2013, 09:21:27 pm »

Balanced differential power is one of those good ideas on paper. Instead of 120V humming into every high impedance guitar coil, or high impedance signal lead, we have 60V and the symmetrical mirror image opposite polarity 60V so capacitive coupling to nodes, symmetrical to both legs will cancel (in theory). Half voltage with the potential to cancel to zip, is a good thing to people chasing hum problems.

While a fuse on the primary should protect against over current, conventional GFCI my have trouble. Perhaps 2x GFCI? one for each polarity?  Or just forget this silly stuff. 


JR



PS: Not to get all pedantic but in terms of electrical wiring verbiage , the two 60v legs are the same phase, but opposite polarity. 
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Jeff Bankston

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Re: Balanced Power Questions
« Reply #8 on: November 24, 2013, 10:49:44 pm »

what about 2 pole 220v to elimimate hum ? 2 hot legs and a ground to an equipment transformer.
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Tommy Peel

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Re: Balanced Power Questions
« Reply #9 on: November 24, 2013, 11:31:14 pm »

Just out of curiosity I looked up one of the Furman units mentioned... $2500, 3 rack units, and 90 lbs for 20 amps of balanced power. On the bright side there's a convenient front mounted USB charger so you can charger your phone with it.  ;D
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Re: Balanced Power Questions
« Reply #9 on: November 24, 2013, 11:31:14 pm »


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