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However, a conventional single-voltage amplifier would be prohibitively large and expensive if it were designed to deliver several times its normal rated output for that length of time. NAD studies indicated that actual high-level music transients are likely to last much longer than the 20 milliseconds of the standard EIA dynamic power measurement, and that considerably more than the continuous power level might be required for several hundred milliseconds. Since the switch to a higher supply voltage occurs at the 140-watt level, any switching transients are masked by the high acoustic level.Ī number of protection systems were built into the 2200, one of the most interesting of which is the "thermal feedback" that protects the high-voltage supply and the output transistors. Because of its conservative design, its clipping power output, even in the "low power" mode, is about 140 watts per channel. NAD chose to design the 2200 as an inherently powerful amplifier, with the size, weight, and heat-dissipating ability (as well as the price) of a typical 100-watt unit. On the other hand, the switching often produces a transient "glitch" on the waveform, which could conceivably be audible, at the point where the supply voltage increases. This arrangement offers economies in manufacture, since most of the time the amplifier generates little heat and requires a small heat-dissipating surface. In some amplifiers it occurs at a fairly low power output, such as 15 watts. One key difference between the 2200 and most other switched-voltage amplifiers is the choice of the power level at which the changeover occurs. The output transistors of the NAD 2200 amplifier are high-powered, fast-switching devices capable of delivering some 60 amperes of peak current for brief periods. Instead, the amplifier can use a relatively compact, inexpensive, low-voltage power supply almost 100 percent of the time, augmented by a second, higher-voltage supply that comes into action only as needed.
#Nad 2200 for large advent speaker full#
Since the average power requirement is usually one-tenth or less of the peak power demand, the switched-voltage design approach offers the attractive possibility of doing without a large, expensive, heavy-duty power supply whose full output will be needed for only a small fraction of the time.
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One way to achieve it is by using a signal-controlled, or "smart," power supply, in which the output voltage is controlled by the instantaneous signal level and automatically adjusts itself to accommodate the brief high peak levels found in most musical and vocal waveforms.
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The importance of high dynamic power output for realistic music reproduction has been widely recognized for some years. If that is not enough, the amplifier can also be operated in a bridged (mono) mode, in which it is rated to deliver up to 400 watts of continuous output into 8 ohms-or, in terms of dynamic power, 1,200 watts into 8 ohms and 1,600 watts into 4 ohms! It is also said to have a wide "dynamic power envelope," which means that it can maintain these high levels for longer than the standard 20-ms bursts. Its dynamic headroom is rated at 6 dB, which means that it can deliver-in 20-millisecond bursts, twice per second-400 watts per channel to 8 ohms, 600 watts to 4 ohms, and 800 watts to 2-ohm loads. However, the NAD 2200-which the manufacturer calls the "Power Tracker"-has some remarkable dynamic power capabilities. Not surprisingly, it follows the NAD tradition of giving its amplifiers conservative power ratings and the ability to drive low-impedance speaker loads without difficulty (the clipping power output is specified as 140 watts into 8 ohms or 200 watts into 4 ohms). In size, weight, and price, it is similar to a number of other good 100-watt amplifiers. It carries a relatively moderate power rating of 100 watts per channel into 8-ohm loads from 20 to 20,000 Hz with no more than 0.03 percent distortion. Despite its conventional appearance, the NAD 2200 is radically different from other stereo power amplifiers in its design and performance, some aspects of which border on the spectacular.