Product Review

ExactPower SP15Ax4 Balanced AC Power Conditioner

April, 2006

Kris Deering



Total Power Delivery: 1800 watts
Four 500 Watt Toroidal Transformers
Four GFI, 15 Amp Hubble NEMA Duplex Receptacles
Each Outlet Individually Balanced
Available with or without EMI/RFI Filtering
120/220/230/240 Volt Availability
Dimensions: 3.5" H x 17" W x 14.2" D
Weight: 56 Pounds
MSRP: $1599.99 USA




In the world of home theater and hi-fi products, there are a lot of accessories that may or may not benefit you in the long run. But, I assure you the temptation is there to spring lots of money on them over time.

As this hobby develops, it seems the ability to just let things be and leave the system alone diminishes at an exponential rate. The room that yesterday you were ecstatic with now has a hint of something that may or may not be a few placebos flying around. Either that or the night before you dreamed of greater possibilities. This is continually fueled by the worst unknown enemy of the enthusiast: the A/V forums. These forums will perpetuate rumors, snake oil, and who knows what else until you drive yourself crazy about how you just wasted all your money on something that appears to be the worst product on the market.


Power conditioning falls into the accessory category but it may or may not be an essential element in a home theater system. There are a lot of heated discussions over how useful these things really are in the end because of the fact that AC power is eventually converted to DC power in your component and unless the power supply within that component is screwed up, most if not all of the noise inherent in that incoming power will be eliminated anyway. While this is true to a point, it is always better to feed a power supply a clean, stable voltage to eliminate the possibility of noise or fluctuations that may actually harm the products in your equipment rack.  

Balanced power is not a new design or approach in power conditioning. It is a rather simple concept. In your home, the AC wall socket that you normally use has three conductors: hot, neutral, and ground. Normally, if you measure the hot to ground you should get 120 volts, and if you measure the neutral to ground you should get 0 volts, but often, this is not what happens, i.e., hot vs. ground might be less than 120 volts, and neutral vs. ground might be 2 or 3 volts.

In a balanced AC circuit, hot vs. ground, and neutral vs. ground will both read 60 volts. In other words, the hot and neutral conductors are both at 60 volts. Since these voltages are of opposite polarity though, and given that most interference in a typical AC line is common between the two lines, the noise in the lines is eliminated when the two lines are added together. This is effectively known as Common Mode Rejection (CMR). You also see this principle put to use in audio systems that use a balanced topology. These are generally very expensive since these types of audio paths require essentially twice the parts (complete paths for both the positive and negative signal).


We have tested ExactPower products over the years, and whether it was on the bench or in subjective evaluation, they have proved themselves to be a valuable addition to any system. Their initial units cleaned up the power, but it was not balanced. So, ExactPower then added the SP-15, which was a balanced power transformer that relied on a single transformer for all of its outlets. While this will usually provide more power to a single outlet in use, it won't do as good of a job eliminating ground loop hum that may come into play when you have a lot of components connected to the same unit. For this review I received Exact Power's newest balanced transformer(s), the SP-15Ax4.

The Goods

The SP-15Ax4 delivers the same amount of total power (1,800 watts) as the SP-15, but instead of using one large transformer, it uses four 500 watt transformers that are completely isolated from each other after the input stage. Each transformer supplies an individual GFI Hubble outlet (each outlet has two sockets) for the best connection possible. Each of these outlets has reset switch on it in case of tripping.

This is particularly useful for components that may send a spike back into the power conditioner when you turn it on or off. If this happens, that outlet will trip and isolate itself from the others protecting the rest of your components. I have used several components that have done this over the years with the most recent being the Xbox 360. Whenever I try to plug this component into the SP-15Ax4 it will trip the breaker on that outlet. A simple reset (pushing a button on the outlet between the two sockets) fixes the issue, but at least I know that the rest of the components connected to the SP-15Ax4 have been kept out of harm's way.  

There are some drawbacks to balanced power transformers in home theater applications, especially when you are using separate transformers for each outlet. Since each transformer is only rated at 500 watts, you are limited in total output power for each outlet. ExactPower states several times both in the manual and on the website that this product is not intended for use with any big amplifiers or high current devices. It is intended more for source components and digital devices such as surround sound processors (SSPs), CD players, DVD players, and video processors. For high current support, they recommend using their EP line of conditioners (purifiers) that deliver 15 amperes.  

In my configuration, I have an ExactPower EP-15A plugged right into the wall with the SP-15x4 plugged into that. This gives me line conditioning as well as balanced power, and essentially complete piece of mind with my power. The only thing this duo does not offer is uninterrupted power via a battery backup. While these are nice to have for PCs and display devices that require cool down (bulb based rear and front projection displays), they usually rely on an AC regenerator that is current limited.

I do not have my display connected to the ExactPower package. It is on a completely separate circuit that is supplying an outlet in my crawl space. My power amplifiers are all connected directly to the EP15A, and all of my source components and my surround processor are connected to the SP-15Ax4.  

The SP-15Ax4 can be ordered with or without EMI filtering. This is because the EP15 products already have EMI filtering so it is not necessary if you already have an EP15. The unit I received did not have the additional filtering.

As mentioned before, each outlet is a premium grade GFI, 15 amp, isolated, full contact Hubble NEMA duplex outlet. Trying to get a power plug into any outlet can be a bit of a struggle as the connectors inside really clamp down. Trying to get the power plug out is even harder. This is exactly what I look for in an outlet. Cheap outlets tend to have play, and plugs can come out easy or create a shock hazard by hanging out partially. The SP-15Ax4 can be ordered with our without rack mounts and comes in silver or black finish.


Set-up of this unit was a breeze. The SP-15Ax4 is essentially just a large box with outlets on the back. There are no special buttons, meters, or displays to navigate. The front face is simply a milled piece of brushed steel that is elegant but unobtrusive. There is a single power button on the front panel with a power LED above it. Once you plug in all of the components it will feed ,you simply turn it on.

In Use

After installation, the first thing I wanted to see is if the unit reduced the noise coming out of my speakers with nothing playing. Regardless of what I've used in the past, there was still a very small amount of low level noise emanating from the tweeters of my speakers. I could hear it unless I put my ear right to the tweeter, but it was there. The SP-15Ax4 completely eliminated this.

I suspect the noise was ground loop related. Since each of the four transformers are completely isolated from each other, the ground loop is interrupted.

On the subjective side I didn't really notice any real change at all in the character of my sound or picture. Since I had been using the EP-15 for some years now and since all of my equipment is on its own dedicated circuit, I wasn't really expecting much of an improvement. The SP15Ax4 did its job of isolating the components from each other and eliminating any noise that the EP15 may not have taken care of already. The GFI circuits did their part several times during this review. As mentioned before, the power supply for the new Xbox 360 tripped the receptacle a few times during my installation as did one of the video processors I got in for review. 

I was delighted with lack of noise from the speakers during quiet music or movie scenes. Dynamics were slightly better than before due to the quieter noise floor but since the noise was only slight originally, the difference wasn't night and day.

I also noticed that the SP15Ax4 eliminated the noise produced by a light that uses a variable output slider. This kind of light is notorious for introducing a buzzing sound in audio systems. Since variable lighting controls are common in home theaters, you can forget about that problem when using the SP15Ax4.


As with all power conditioning products, I highly recommend evaluating your power needs before proceeding. However, the chances are, if you live in a highly populated area (i.e., not on a 10,000 acre farm in the middle of Kansas), you probably have dirty AC power. Something like the ExactPower SP15Ax4 can really help.

But you also have to remember that these products sometimes do even more than clean up your power, they protect your components.

The combination of the EP15A and SP15Ax4 represents an expensive investment, but every power issue I've ever run into has been completely eliminated by having them. From dimming, noise, and trips, the duo has eliminated them all. To this day, I don't think I've recommended a product line more.

- Kris Deering -

Copyright 2006 Secrets of Home Theater & High Fidelity

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