NAD 2140 (c. 1980–1983)
The NAD 2140 is a stereo power amplifier from the early 1980s. It is built around NAD's "Power-Drive" architecture, a dual-mode design that behaves as a high-current voltage source at moderate levels and switches toward a high-current current source as output rises. This was NAD chief engineer Bjorn Erik Edvardsen's approach to letting a modestly-rated amp handle difficult, low-impedance speaker loads without strain. The 2140 also has NAD's defeatable Soft-Clipping circuit, which gently rounds signal peaks to avoid harsh clipping when the amp is pushed.
NAD sold it as part of its "affordable high-end" line of the era, frequently paired with the NAD 1150 preamplifier. It is a power amplifier only - no phono stage, no pre section. The front panel is minimal and has no power switch. That lives on the back, and owners regularly mention it.
Inside, the 2140 has a toroidal transformer shared by both channels (not a true dual-mono design), a symmetrical JFET differential input stage, and two 10,000µF filter capacitors. There are no output relays. The output is direct-coupled with only an internal fuse, so a failed output transistor can send DC to your speakers. That's a known failure mode. Output transistors are prone to thermal-cycling failure and are commonly replaced with On-Semi MJ15003/15004 parts. Filter capacitor aging is another recurring issue. The service manual is scarce, and HiFi Engine carries only a limited user manual, which leaves a real gap for the repair community.
Rated output is disputed across sources. Figures of 60W, 75W, and 80W per channel into 8Ω all circulate, and the 2Ω rating in one source (2×35W) is physically implausible and likely a typo. Owners agree that the amp feels more powerful than its conservative rating suggests and handles 4Ω loads comfortably. S/N ratio is quoted at better than 90dB (one source) or >95dB unweighted / >110dB IHF A-weighted (another). Frequency response is ±0.15dB across 20Hz - 20kHz. Dimensions are 440 × 92 × 251 mm, and weight is 6 kg.
HiFI-Stereo (December 1984, p.65) mentioned the 2140 in a system profile. It was an enthusiast's setup using the amp to drive delay speakers in a large listening room, alongside ProAc Studio 3 mains and an Audio Pulse digital time-delay unit.
Owner consensus, per HiFi Engine comments, calls it "one of NAD's best made amps from the 80s." Typical current pricing on the used market runs $150 - $250 USD, up noticeably from the $75 - $100 range a few years ago. The sound is described as smooth and non-fatiguing, the classic NAD house character, with punchy bass and slightly soft highs.
Known specs (as documented)
- Output: 60W–80W per channel into 8Ω (source conflict; see above)
- Input sensitivity: 1.25V
- Input impedance: 50kΩ
- Damping factor: >60
- Dimensions: 440 × 92 × 251 mm; 6 kg
- Power-Drive architecture with defeatable Soft-Clipping
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