Power sells products, from automobiles to amplifiers. Moreover, whether it is the horsepower required to accelerate onto a highway safely, or the reserve power to sustain complex musical peaks or movie sound effects played effortlessly, real power is the main ingredient that creates realism.
So it is unfortunate that 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 pop fiction than reality.
Currently, the U.S. government’s Federal Trade Commission (FTC) guidelines for amplifier power ratings are so minimal that a large number of amplifiers and receivers on sale today only seem powerful?on paper. In reality, these numbers are often meaningless; these products in most cases will not deliver the power- the real power you thought you were purchasing. The FTC requirement is based entirely on measurements derived from an 8-ohm resistive load, with only two “adjacent” channels driven. To further undermine the issue of real amplifier performance, manufacturers are only mandated to sample their measurements at an easy 1 kHz frequency- no distortion specification required!
Unfortunately, far to many manufacturers have resorted to publishing “marketing” specs that generate the largest possible “number” attainable when representing their power ratings. One of the easiest methods to achieve this goal and one most often employed, is to engage a very soft (poorly regulated) power supply. This type of power supply produces an extremely high voltage without a load (or when driving a very easy load). However, the voltage sags dramatically when connected to a complex loudspeaker load. This little “secret” is the reason why many manufacturers do not fully disclose their power rating under all operating conditions. Too often, the”100 watt” receiver can only deliver a fraction of the power when connected to a loudspeaker, particularly when all channels are driven simultaneously in a multi-channel system. Perhaps even worse, many of these designs also employ V/I Limiting (current limiting, a Draconian approach to amplifier protection circuitry), resulting in sound quality that is diluted, overly bright, and lacking in musical integrity.
Another element that is used to describe power specifications is dynamic power. Since real world program material generally requires only momentary bursts of high power rather than the continuous power normally specified, many manufacturers do not even attempt to provide these fundamental ratings since it is not a requirement of the FTC. All too often, actual continuous power is far less than promised. So when driving 5, 6, or 7 loudspeakers, the dynamic power required to reproduce the resonant intensity of an action scene or an orchestral climax is non-existent and the amplifier resorts to distortion (clipping).
At NAD, we have always been and will continue to be very conservative when publishing our power ratings. We prefer to state the guaranteed minimum rather than the optimistic “best case” fantasy offered by many of our competitors. Therefore, while our bottom-line advice always has been to listen and judge those performance qualities that specs cannot possibly describe, we also want our specs to truthfully represent our products to the extent that they conceivably can. To realize this goal, we have developed a design concept that we refer to as “Full-Disclosure Power”. This criterion is far stricter and consequently produces a more conservative and accurate power rating, than the FTC requirement. All of our rating specifications are measured with all channels driven simultaneously, full bandwidth 20Hz to 20kHz, at rated distortion, into either 4 or 8 ohms.
It is our conviction that the inclusion of dynamic power ratings is essential in the accurate portrayal of available power from an amplifier. Therefore, we also rate our amplifier’s dynamic power at 8, 4, and 2-ohms. We have observed that most receivers go into full protection mode when presented with a 2-ohm load. Only an amplifier with high-current power supplies, sonically transparent protection circuitry, and heavy-duty discrete output stages will measure up to this challenge. So to clearly distinguish our Full-Disclosure Power ratings from the skeletal FTC standard, and provide the consumer the most truthful description of our -world performance, we specify the dynamic power of all NAD amplifiers. The circuit technology that enables our amplifiers to realize specified power and deliver the “juice” to any loudspeaker without regard to impedance variation, is called PowerDrive?.
PowerDrive? NAD’s patented PowerDrive? amplifier circuit was created to address the diverse and demanding requirerments of high dynamic power and high current drive capability. By incorporating a second high-voltage rail to our well regulated, high current, power supply as an adjunct to our amplifier circuit design, we achieve the operational capability of “over-drive”. This performance feature has the benefit of nearly doubling the power on a short-term dynamic basis. Further NAD’s “smart” power supply can optimize itself for high current or high voltage delivery, depending on the specific operational conditions. In addition to the above-mentioned benefits, PowerDrive? offers improved amplifier stability with low impedance drive capacity and a significant reduction in distortion.
In selected, higher-end NAD power amplifiers and receivers, we also employ upgraded toroidal transformers with highly specified, tightly toleranced smoothing capacitors (design objectives and cost permitting) to improve dynamic power and reliability. This circuit topology has actually facilitated an increased capacity for dynamic power and in most cases, increases have measured an incredible 30 to 60 watts per channel (depending on impedance).
NAD’s Full Disclosure Power Rating is an earnest attempt to bring a broader understanding to the power ratings issue. Specs are, by their very nature just a “snapshot” of an amplifier or receiver’s capability. In the end, it’s not the ratings you listen to; rather it is music or movies played through loudspeakers in your listening room. Consumers have a right to a “level playing field”, armed with authentic specifications. Unfortunately, today the basic power ratings of 100-watts is totally inadequate and in some instances too misleading to serve any usefulness for the consumer to discern real value choices. We believe full disclosure power rating specifications should be an industry standard and to that end, hope other manufacturers accept this premise when publishing amplifier specifications.