How does balanced power help to solve ground loop humming

Using balanced power solves ground loop problems because it takes it's ground from one source, hence no potential difference. You can do this yourself simply by taking all power from one spot. If your equipments "leak" to the ground, then balanced power might be helpful.

How does balanced power work ?

Balanced power systems have been most commonly used with the 120V mains power used in USA. In normal wiring there is one neutral wire which is always at (almost) ground potential and other wire which carries the 12V AC voltage. There is also a separate safety ground wire.

In balanced power there is two out of phase 60V lines rather than normal 120V and neutral. The voltage difference between those out of phase 60V lines is 120V, so the equipments will get full 120V between their power input pins. The balanced power is generated from normal AC voltage by using an isolation transformer with centre-tapped 120V output and the centre-tap of the output is grounded.

That expensive power balancing equipment is just a 1:1 mains power isolation transformer with a center tap to ground, so that you have two legs of AC which are 180' out of phase with respect to one another (with respect to ground), so that your ground currents cancel out. The important fact not noted is that the center tap is also situated as a the center of the output voltage swing. That's the key in a balanced power system. Balanced power is not high tech stuff.

Power transformers don't need to be wideband, they don't need to have extremely low distortion, and they don't need to work on a wide variety of different voltages with extreme linearity. On the other hand, they do need to be able to work into a wide variety of loads. The transformers used in balanced power units are specially would toroid transformers. The windings have to match perfectly or the "balanced" aspect of the power doesn't work!

How is the balanced power claimed to help ?

The manufacturers of balanced power systems claims that balanced power solves all ground loop problems in audio and video systems. Typical claims are also that you get much better noise margin.

If you have chassis leakage problems, it can be a miracle. If you don't, it doesn't do any better than any other isolation transformer.

I haven't had the need to use balanced power, but in theory it solves similar problems in a similar manner that a balanced audio signal does; namely noise cancellation. Not to blindly be relied on to fix everything or to be a substitute for careful troubleshooting.

The typical claim made by the the salesman of balanced poer is: "When the power is balanced the mains cable has less electric field around them so they should induce less noise to nearby audio cables". Those clames are partially true, partially quite nonsense. If you placed an unscreened cable next to a balanced power cable, I would expect that less noise/hum would be picked up as the hum is capacitively coupled. If you placed a screened cable next to a balanced power cable, quite little difference would result if any. The capacitively coupled signal is now intercepted nearly completely by the screen. Practically only the magnetically coupled component will reach the screened signal wire(s). Magnetic field around the cable will be practically the same whether the mains cable is balanced or not as there is still the same mains current flowing up one wire & back down the other.

Balanced power can solve the ground leakage problems caused mostly by computers and baddly designed audio equipments (mostly guitar amplifiers). When the leakage current is redicud to none using balanced power there is less noise in the ground wire. If you have a chassis leakage problem, balanced power will radically reduce your noise floor. If you don't, it won't help in your system.

If your noise is all hissy white noise from noisy electronics, balanced power won't do a thing. If your noise is mostly hum from power supply leakage on bad equipment (especially old guitar amps), it can do an amazing job. If it's hum from ground loops, it won't do anything (or anything more than plugging all your equipments to one extension cord). Balanced power is a particular tool to solve a particular problem.

Because balanced power uses isolation transformer this can help to stop some interferences from mains power to enter you audio equipment power system. But simple transformer does not usually do much help on this either.

Tips on buying balanced power systems

Sometimes balanced power helps, sometimes it doesn't, and it's nearly impossible to predict. The only advice I can offer is to buy from a dealer who will let you return it. But if you're having a hum problem, try to fix it by studying out your system grounds first. Equipment that is designed, built, and connected correctly shouldn't need a balanced power source to make basic problems go away. You probably can't do anything about the equipment design or construction (some people modify internal wiring to correct a manufacturing deficiency) but you can, by isolation procedures, examine your grounding and shielding to make sure you haven't created a problem.

Who makes balanced power systems

Where I can find more information on balanced power systems ?

The following links to balanced power articles should give you a good overview of the balanced power systems. Remember that most of those articles are written by the manufacturers of balanced power systems.

There are other alternatives than balanced power

If you are looking to quiet down a studio you have also other alternatives than just go straight to balanced power system. Usually the ground loop induced humming problems can be solved with carefully designed audio and mains wiring. Taking the power for all equipments from single source usually keeps the humming problems away if the equipments are properly designed connected together in the right way.

Try a good common isolation transformer if you are trying to solve power line borne problems. And good quality 1:1 audio isolation transformer in problematic audio lines will always help you to get rid of humming and noise.

Some on-line UPS equipments provide galvanic isolation and good mains power noise reductions. UPS also provides you some safety against high voltage spikes and power interruptions. Be prepared to buy a good UPS with sinewave output because if the UPS output is not good sinewave you can get noise problems because of bad power that the UPS gives out. Stay away from the cheapest computer UPSes. The problem with these is that they have a lot of line harmonics on them, and they can make noise problems worse for that reason.


Tomi Engdahl <Tomi.Engdahl@iki.fi>