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NAD Full Disclosure Power

October 4, 2006

Power sells products, from automobiles to amplifiers. And whether it's the reserve power needed to pass another car on the highway safely, or the ability to cruise along at high speed with the engine unstressed, or the chance to enjoy complex music or movie effects played loudly without strain or edginess, real power can make a real difference.

Unfortunately, though, the power output ratings of amplifiers and receivers are not as easily comparable and reliable as horsepower. The power specs for today's amplifiers and receivers can be—and often are—more a matter of appearance than reality. Manufacturers jockey for specs that look good on paper, but these numbers may not deliver the real power and the real listening advantages for which you are buying good AV equipment.

NAD has always been intent on giving prospective buyers the best possible sense of what a product will really do. So while our bottom-line advice always has been to listen for yourself and judge all the qualities that specs can't fully describe, we have always wanted our specs to describe as much as they possibly can—and have also wanted our effective power to be even more than standard specifications may be able to indicate.

This seems even more important to us now, when new power ratings developed by the U.S. government's Federal Trade Commission (FTC) seem likely to make mediocre equipment seem more powerful than it really is. So we've developed a concept we are calling "Full-Disclosure Power." To describe it, let's start behind the scenes.

Many manufacturers pull every trick out of the book to try to get the biggest possible number for the power spec. The easiest means to this end, and the one most often employed, is to use a very soft (poorly regulated) power supply. This type of power supply will give a very high voltage when not driving a load (or driving a very easy load), but the voltage sags badly when presented with a complex loudspeaker load. This little "secret" is the reason why many products do not fully disclose their power under all operating conditions. Many "100 watt" receivers can only deliver a fraction of that when connected to a real loudspeaker and/or when all channels are driven. Perhaps even worse, most of these designs also employ V/I Limiting (a Draconian approach to amplifier protection circuitry), resulting in sound quality that can sound very thin, overly bright, and lacking musical texture. And since the power is far less than "promised" when driving 5 or 6 real loudspeakers, the dynamic power required for the full intensity of a movie action scene or orchestral climax is simply not available.

THD Comparison

NAD's approach, on the other hand, is to optimize its power supply to properly drive real-world loudspeakers. This means a properly regulated, high-current power supply is supplied in all NAD amplifiers and receivers. Thus we can rate our receivers with a difficult 4-Ohm load, with ALL channels driven simultaneously, over the FULL frequency bandwidth (20Hz - 20kHz), and at rated distortion. This is the Full-Disclosure rating method on which all our amplifier and receiver specs are based, and it's a far cry from the FTC's minimal requirement of using an 8 Ohm load, any channel (singular), at an easy 1 kHz frequency, with no distortion specified!

Dynamic Power

Another aspect of power specification long championed by NAD is dynamic power. Since real-world program material requires short bursts of very high power rather than the continuous power normally specified, we also include dynamic power ratings at 8 Ohms, 4 Ohms, and even 2 Ohms! Most receivers will go into full protection mode when presented with a 2-Ohm load, but NAD's high-current power supplies, sonically transparent protection circuitry, and heavy duty output stage are easily up to the task. So to further distinguish our Full-Disclosure ratings from the barebones FTC standard, and give the consumer the most realistic description we can of real-world performance, we also specify the dynamic power our amplifiers deliver to speakers of varying impedances. And to maximize this real, useful power in daily listening, we've developed an amplifier circuit we call:

POWERDRIVE

To meet the diverse requirements of high current drive and high dynamic power, our patented PowerDrive amplifier circuit will build further on our reputation for amazingly effective power. By adding a second high-voltage rail to our well regulated high-current power supply, we get an "overdrive" that can nearly double the continuous power on a short term dynamic power basis. This is a further development and refinement of our renowned Power Envelope circuit, utilized by NAD in the 80's and 90's. PowerDrive differs from Power Envelope in that it offers greater amplifier stability and low impedance drive capability, resulting in less distortion when driving real speakers with real program material.

SOUND, NOT SPECS

Specs are, by their very nature, just a snapshot of an amplifier or receivers capability. NAD's Full Disclosure Power Rating is an attempt to bring a broader understanding to the power rating issue. But, in the end, it's not ratings you listen to; rather it is music or movies playing through loudspeakers in your listening room. In other words, your own ears will tell you everything you need to know about power. When you listen to the clear and intensely detailed sound of NAD, with its powerful and extended bass, you'll understand why we focus on low impedance drive capability. And when you notice the relaxed and unstressed way an NAD sails through musical and cinematic climaxes, you'll appreciate the engineering behind PowerDrive, with its incredible dynamic power reserves.

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