Stereo power amplifier with Power Guard protection and output transformer-coupled design
Overview
The McIntosh MC2120 is a solid-state stereo power amplifier produced during McIntosh's classic solid-state era. It delivers 120 watts per channel into 8 ohms with exceptionally low distortion across the full audio band. Designed for both performance and speaker protection, it features the proprietary Power Guard system and output transformers that ensure consistent power delivery across all load impedances.
Specifications
| Rated output stereo | 120W+120W |
| Rated output mono | 240W |
| Output load impedance | Stereo: 2Ω, 4Ω, 8Ω, 16Ω; Mono: 1Ω, 2Ω, 4Ω, 8Ω |
| Frequency response | 20 Hz ~ 20 kHz +0 -0.25 dB (at 1W) |
| Total harmonic distortion | 0.1% or less (0.25W–120W, 20Hz–20kHz) |
| Signal-to-noise ratio | 95 dB or more (at rated output) |
| Input Sensitivity / Impedance | 0.75 V, 2.5 V (switching type) / 100k Ω |
| Power consumption | 50W (no signal); 460W (max output) |
| External dimensions | Body: 372W × 127H × 330D mm; Front Panel: 407W × 132H mm |
| Weight | 25.9 kg (net); 31.8 kg (packed) |
| Power supply voltage | 120 VAC, 50Hz/60Hz |
| Semiconductors used | 39 silicon transistors, 2 ICs, 24 silicon diodes |
Design
The MC2120 features a Power Guard system that compares input and output waveforms, lighting a warning lamp at 0.5% difference and activating protection at 1% to prevent clipping and speaker damage. The amplifier uses a monolithic transistor differential input stage for low noise, followed by a class A voltage amplifier. The driver and complementary service circuits operate near class A to minimize crossover distortion, while the power transistors run in class AB. The output stage is a single-ended para-push type using six complementary power transistors. Output is transformer-coupled, allowing full power delivery into any load impedance and providing protection in case of amplifier failure.
Context
The MC2120 is part of McIntosh's "Classic Models" lineup from the solid-state era, representing the brand's commitment to high-fidelity performance and robust engineering.
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