NAD 3020 - Manual (Page 2)

HIGH-PERFORMANCE DESIGN
Wide Range Phono Preamplifier
In a moderately priced amplifier you might expect to find an economy preamp circuit, but the NAD
3020 contains a phono preamp stage which is audibly identical to the finest separate professional
preamps. The 3020 preamp interfaces correctly with the impedances of real phono cartridges (as many
preamps do not), it is quiet enough for use with either moving-magnet or high-output moving-coil
pickups, and its distortion is extremely low, not only with sine-wave test tones but also when
reproducing complex high-level music signals. The 3020 was designed to achieve the best signal/noise
ratio when a cartridge is plugged in (rather than with the usual, but inappropriate, short-circuit input).
The total dynamic range of the 3020 is typically 107dB, ample even for the digitally-mastered recordings
of the 1980s.
Infrasonic and Ultrasonic Filters
Audio signals are often contaminated with interference at frequencies below and above the audible
range, such as acoustic feedback, disc warps and radio interference.
Amplification of such signals yields no sonic benefit, wastes amplifier power, and may cause
intermodulation distortion muddy bass, excessive woofer cone motions, and even tweeter burnout. The
NAD 3020 contains a precise, minimum-phase audio-bandpass filter which strips off such interference
and preserves a clean musical waveform.
High-Voltage High-Current Output Stage
Although the 3020 is rated at 20 watts/channel, it behaves as if it were much more powerful. Its high-
voltage design yields an IHF Dynamic Headroom factor of 3.0 dB, meaning that in musical transients the
3020 can deliver twice its rated power or 40 watts into an 8-ohm impedance.
Even more important is the amplifier’s interface with the highly variable impedances of real
loudspeakers, which often are much lower than 8 ohms and partly “reactive” with high peak current
demands. The output transistors in the 3020 are the same large devices which other manufacturers
employ in their “60 watt” amplifiers, and in musical transients the 3020 will easily deliver over 58
watts/channel into 4 ohms or over 72 watts/channel into a low 2-ohm impedance, with no distortion
due to triggering of protection circuitry.
Soft Clipping™
When the 3020 amplifier is overdriven beyond its rated power, the exclusive NAD Soft Clipping™ circuit
gently limits the waveform voltage so that the output transistors are never driven into saturation, i.e.
into “hard clipping.” This feature eliminates the harsh power-supply buzz and some of the distortion
which hard clipping normally would cause, thus the 3020 can be overdriven substantially beyond its
rated power cleanly and safely.
Dual-Mode Power Supply
The power supply circuit for the output stage is only loosely regulated, so it is free to supply the high
voltages needed for a high IHF headroom factor (at 8 ohms) and also to supply the large currents at
lower voltages needed for driving low-impedance loads (down to 2 ohms). An entirely separate power
supply circuit, operating from another secondary winding on the power transformer, supplies extremely
stable, noise-free, regulated operating voltages for the preamplifier and tone control stages; thus
distortion and blurring of the stereo image due to power supply modulation cannot occur in the 3020.
The NAD 3020 has earned a world-wide reputation among audio reviewers for its sensible and efficient
design and superb performance.
Numerous test reports, comparing the 3020 with equipment of far greater power rating and cost have
proven the 3020 to be an outstanding value.