Product Review - Furman IT-Reference Discrete Balanced Power AC Line Conditioner - December, 2000
John E. Johnson, Jr.
Furman IT-Reference Discrete Balanced AC Line Conditioner
Capacity: 20 Amps Peak, 12 Amps Continuous
Outputs: 6 AC Outlets (120 Volts RMS); Four Outlets Have Discrete Balanced Filtered AC; Two Outlets Have Filtered (but not Balanced) AC for Power Amplifiers
Size: 5 1/2" H x 17" W x 16" D
Weight: 80 pounds
MSRP: $3,000 USA
Furman Sound, Inc. makes products for the professional market, including musicians. They started out with audio signal processors and expanded into AC power conditioners. They now have a product line of about 75 items. Since their line has primarily been pro gear, you may not have heard of them in the consumer audio and home theater market. That is one reason why I wanted to review their new IT-Reference AC line conditioner. Professional gear tends to have massive build quality, and the IT-Ref weighs 80 pounds, just to clean up your AC power! As we all know, in our home theaters, we have so many components connected to each other, often on a series of power strips, ground loops are a big problem. The IT-Ref was designed with home theater in mind. It has four separate isolation transformers that deliver balanced power, but also each having its own isolated ground.
Here is how the balanced power is delivered. The incoming AC is connected to the primary windings on the isolation transformer. The secondary is connected to the output AC sockets. The ground for the output socket is actually a connection to a center tap on the secondary windings. Since each of the four isolation circuits (labeled A, B, C, and D in the photo below) has its own center tap on its own isolation transformer, each of these four circuits has an isolated ground. Therefore, you can't get a ground loop between components that are plugged into the four separate circuits, even though the components are connected together with audio cables. Also, each of the four isolation circuits has balanced (Furman calls it symmetrical) AC. If you measure the voltage in one of your grounded AC outlets in your home, you will find that it measures one voltage between the hot and ground, and a different voltage between the neutral and ground. With the IT-Ref, it will measure 60 volts on one and 60 volts on the other. The voltage between the hot and neutral is 120 volts, and that's balanced power. The IT-Ref differs from other products in that it has the four isolated circuits rather than one big circuit. This approach is specifically for preventing ground loops, but has other advantages as well (see below).
One problem with some line conditioners is that they have so many things in the circuit, the output impedance is raised, which limits the current that can flow. This can affect the performance of components plugged into it. Furman has addressed this issue specifically in the IT-Ref by using a proprietary toroidal transformer that has such low impedance, it will draw 200 amps for 0.25 seconds when you turn the unit on. In order to prevent your circuit breaker from tripping, Furman put in a soft start feature. This lets the transformer charge up slowly, and then power is applied to the output sockets. The IT-Ref has Ground Fault protection built-in, and there is a test button on the front panel, which Furman suggests you use once a month to make sure everything is OK.
Two of the IT-Ref circuits are filtered, but not balanced (the two sets of sockets on the far left in the above photo). These are for big power amplifiers. The isolation transformer would be huge, so these two circuits don't have one. However, I found that as long as I just used a reasonable size power amplifier, I could plug it into one of the balanced circuits without any problem (no blown fuses). So, I was able to test the the IT-Ref with a Balanced Audio Technology VK-5i tube preamplifier plugged into one balanced circuit, and a Balanced Audio Technology VK-75SE tube power amplifier (75 watts per channel) plugged into a second balanced circuit. I also plugged a Sunfire Subwoofer into one of the balanced circuits, and a CD player into the fourth balanced circuit. Everything was fine this way. I used Monitor Audio Studio 20 SE floor-standing speakers and Nordost cables in the test.
The VK-5i and 75SE are a spectacular sounding pair of components regardless of the AC situation, but with the IT-Ref, a very thin veil that I did not know had been there, was lifted. The clarity was now like a crystal goblet that was squeaky clean. I could hear the rosin on the violin strings as if I were playing the instrument myself. The number of trumpets was distinguishable.
There are several reasons why the Furman IT-Reference made a difference in my system. One is that balanced power will eliminate common mode noise of all frequencies, including RF. Secondly, the filters in the IT-Ref remove non-common mode noise. Even though RF is outside the audible band, it interacts with the low level detail (e.g., 50 dB - 80 dB below the primary part of the music) to mask it. And it is the details that make the music sound live. The rosin on the violin strings that I mentioned above, for example. Instruments like triangles have a lot of harmonics, and the upper harmonics are masked by RF getting into the circuit. Power lines are like huge antennae, picking up RF and other noise before they come into your house. Tube equipment is particularly vulnerable because they tend to have high impedance inputs, where RF will bombard them. But all equipment, solid state and tube, will benefit from the removal of noise that would otherwise be piped in through the AC power cord.
The four isolated power banks not only control ground loop, but will prevent backwash noise (each component produces back EMF) from passing backward through the power cord of each component and getting into the power cords of the other components plugged into that same socket. This is a feature apparently not offered by other AC line conditioners, and the cost of building it with four separate banks is one major reason why the IT-Ref is $3,000.
In the evening, the IT-Ref often had some rather loud mechanical hum, coming from the toroidal transformer. This indicated that my AC supply had some DC in it. So, I went around the lab, turning off any unneeded lights, especially those on rheostats. This reduced the hum. Fortunately, DC will not pass through a transformer, and this is another reason that an isolation transformer can help keep nasties out of the amplifier power supply. My White Audio B-80 monoblocks used to hum like crazy in the evening, when they were plugged into the wall. I plugged them into the Furman in the evening when the IT-Ref was humming away, and the B-80s hardly made any mechanical noise at all. Better to have the Furman dealing with bad AC than the power amplifiers.
Mass market products will not benefit as much from the IT-Ref, because they have other design flaws that prevent the fine detail from going through to begin with. However, the will benefit to some extent from AC noise reduction, and assuming you would plug your TV, DVD player, VCR, receiver, and outboard power amplifier into it, the cost is still reasonable assuming you want the very best out of your equipment. Garth Powell, who designed the IT-Reference, said that Furman is coming out with several new home theater products in the next couple of months, so you might want to check their website. The IT-Reference is their flagship product, and the rest of their line, which will do most of what the IT-Ref will do, are much less expensive.
Now that Secrets has shown conclusive evidence that AC line conditioners do make a measurable difference (using an Audio Precision test instrument) as to the amount of noise in DVD players that are connected to them (see some of our recent DVD player reviews), buying a good line conditioner is a no-brainer. Certainly, the Furman IT-Reference is a superb member of that product category.
- John E. Johnson, Jr. -
© Copyright 2000 Secrets of Home Theater & High Fidelity
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