2200 Power Amplifier
Date of manufacture : Jan 87 - Feb 89
Please note that this document contains the text from the original product brochure, and some technical statements may now be out of date
Reproducing musical signals, the NAD 2200 routinely delivers over 500 watts per channel into typical loudspeaker impedances.
In actual measurement with speakers of complex impedance and lower-than-average sensitivity, the 2200 produces peak sound pressure levels exceeding 115 dB SPL(Sound Pressure Level) in a medium to large room, with no audible or measurable distortion.
But in size, heat dissipation, and cost, the NAD 2200 is similar to many other amplifiers rated at only 100 watts per channel. For audiophiles who can use and appreciate its capability, the 2200 is unquestionably the best-buy power amplifier ever manufactured.
The Key: Real-World Design
Examined from one perspective, the 2200 is a very conservatively rated 100 watts/channel power amplifier that has an extraordinary +6 dB of dynamic headroom, meaning that it can produce more than four times its rated power during musical transients.
Looked at another way, the 2200 is a super-amplifier that produces between 400 and 800 watts per channel for music (depending on speaker impedance), but contains an “intelligent” power supply that gives it the modest size, heat dissipation, and cost of a conventional 100 W/ch amplifier.
The key to the design of the 2200, as with all NAD amplifiers, is that its design goes beyond conventional specifications and laboratory tests to provide optimum performance under the conditions of everyday use, NAD amplifiers are designed, first and foremost, to reproduce the dynamically varying waveforms of music-not just sine-wave test tones. They are designed to deliver undistorted power to loudspeakers of any impedance-not just to an 8-ohm test resistor. NAD’s engineers have always recognised the importance of supplying high levels of output current to drive the low and complex impedances of real loudspeakers. NAD premiered the use of Soft Clipping™ in solid-state amplifiers to prevent harsh distortion when the demands of the musical signal exceed the amplifier’s limit. All NAD amplifiers feature high dynamic headroom for the transient sounds in music.
The NAD 2200 is a truly “dynamic” power amplifier. Its heart is the unique PowerTracker control circuit (patent pending), which automatically adjusts the amplifier’s maximum power output according to the dynamic character of the signal that is being amplified. As befits a product designed for the reproduction of music, the NAD 2200 achieves its maximum power output of 400 to 800 watts per channel when amplifying wide-range musical signals that contain peaks IO to 20 dB above the average level. But when the amplifier is fed a high and constant signal (i.e. a sine-wave test tone instead of a musical waveform), its maximum output automatically declines to avoid overheating, and eventually levels out between 100 and 200 watts per channel.
The 2200 virtually redefines the concept of dynamic head-room.
Its high power reserves are available, not only for the short 20-millisecond bursts used in the standard IHF dynamic headroom test, but also for musical surges and climaxes lasting ten times longer. Even with compressed recordings of rock music in which the peaks may be only 8 dB higher than the average power, that may be enough variation to allow the 2200 to operate at high efficiency and maintain a clipping level above 500 watts per channel into the 4-ohm impedance that is typical of real speakers.
The appeal of the NAD 2200 may be based mainly on its combination of high dynamic power and low cost, but there are other noteworthy aspects of its design, too.
Transparent sound
The audio circuitry of the 2200 is based on the same principles that gained worldwide praise for other NAD amplifiers. In the 2200 the circuitry is scaled up substantially in speed and power, using the finest selected parts available today-individually tested filter capacitors and ultra high-speed transistors for wide bandwidth and extremely low distortion. The output stage is a fully complementary parallel circuit using high-gain 25MHz transistors with over 10 times the “safe operating area” of transistors used in typical 100 watts/channel designs.
High-voltage, high-current design
Current flowing through the voice-coil is what causes a speaker to produce sound, and NAD was the first manufacturer to emphasise the importance of high output current capacity-unrestricted by so-called protection circuits-to cope with the complex, reactive impatience that many speakers present. The NAD 2200 can produce peak output currents exceeding ±50 Amperes on demand, together with peak output voltages of ±95 volts to handle the most dynamic signals.
Inverted channels for powerful bass
The greatest power demands commonly occur at low frequencies. Bass signals are in phase (and virtually monophonic) in most recordings; thus when the bass waveform is strongly positive in the left channel, it usually is strongly positive in the right channel at the same time. As a result both channels draw current simultaneously from the positive half of the power supply, while the negative half sits idle. During the negative half of the waveform, both channels draw from the negative supply while the positive supply sits idle. In the NAD 2200 the right channel is internally inverted in polarity. When a bass waveform causes the left channel to draw current from the positive supply, the right channel draws its bass power from the negative supply, and vice-versa. This efficient usage halves the instantaneous drain on either supply, allowing much stronger bass to be reproduced without draining the supply.
Bridging
The NAD 2200 is so powerful in the normal stereo mode that few listeners will ever need more. For special situations the two channels of the 2200 can be bridged to form a mono amp of truly immense power. Its rated continuous sine-wave output is 400 watts, while its dynamic power output exceeds 1200 watts into 8 ohms and 1600 watts into 4 ohms.
Two 2200s in bridged mode (delivering over 3 kilowatts into a pair of 4-ohm speakers) would cost about the same as an ordinary 400-watt amplifier.
Quiet circuitry
The delicacy and purity of low-level musical information is as important for realism as the power to handle climaxes. The signal-to-noise ratio of the 2200 (relative to its rated 100 W/ch output level) is greater than Ill dB, No fan noise. In most power amps that are capable of the same 500 W/ch output on musical signals as the 2200, a noisy fan must be used to dissipate excess heat from the circuitry.
The efficient 2200 is totally, blissfully silent in operation.
Close-tracking Soft Clipping™ The newly improved Soft Clipping” circuit in the 2200 accurately tracks the available peak power, regardless of speaker impedance. Older Soft Clipping”” circuits tended to reduce the available dynamic power by 1.5 to 2 dB in order to ensure that continuous output would always be free from harsh distortion (even when the amplifier was over-driven).
With the new PowerTracker™ circuit, this limitation no longer applies. Now the amplifier’s sound remains subjectively clean and transparent right up to the maximum output level. It continues to sound good even at levels 2 to 3 dB above the amplifier’s rated maximum output, since the Soft Clipping circuit gently rounds off the waveform corners and prevents any distortion due to power-supply modulation as well as reducing high order harmonics which may damage tweeters.
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