Mark Levinson No.20 (1986–1990)

A discrete-transistor power amplifier with toroidal transformers, built for solid-state power without compromise.

Overview

The Mark Levinson No.20 came out in 1986. It weighs 95 pounds and cost $9,000, which was a lot of money at the time. It was not a hobbyist's amp. It was built for mastering engineers, recording studios, and audiophiles with good ears and deep pockets. It stood in control rooms where mixes were finalized and in listening rooms where silence mattered as much as sound.

It puts out 150 watts per channel into 8 ohms, which was serious power in 1986. The way it delivers that power is the interesting part. Many amplifiers of its era used global negative feedback to smooth over imperfections. The No.20 rejected it. It uses a fully balanced, discrete transistor design, engineered so that feedback isn't needed to correct its behavior. The result is transparency and dynamic control that left listeners close to the music. It didn't shout; it commanded. Every note was rendered with precision, yet never sterile.

Specifications

Power Output	150 watts per channel into 8 ohms, 250 watts per channel into 4 ohms
Frequency Response	10 Hz to 100 kHz, +0/-1 dB
Total Harmonic Distortion	< 0.01% at 1 kHz, 100 W into 8 ohms
Signal to Noise Ratio	120 dB (ref: 150 W, 20 Hz–20 kHz, A-weighted)
Damping Factor	200 (at 100 Hz, 8 ohms)
Slew Rate	50 V/µs
Gain	27 dB (balanced)
Input Sensitivity	1.4 V RMS for rated output
Input Impedance	40 kohms balanced
Dimensions	19 in × 7.5 in × 19 in (483 mm × 190 mm × 483 mm)
Weight	95 lbs (43.1 kg)
Power Consumption	1500 watts maximum

Key Features

Fully balanced, discrete transistor design with no global negative feedback: This wasn’t just marketing fluff—it was engineering heresy at the time. Most high-power amps used global feedback to reduce distortion, but the No.20’s circuit was so well-matched and symmetrical that it didn’t need it. The result? Faster transients, lower phase distortion, and a soundstage so coherent it felt like the speakers vanished. If you’ve ever heard a live acoustic guitar in a quiet room, the No.20 came closer than almost anything else to replicating that immediacy.
Massive toroidal transformer and extensive capacitor bank: Nestled in its chassis was a 1.5 kVA toroidal transformer—the kind usually found in industrial equipment—paired with a capacitor bank that could power a small town. This wasn’t overkill; it was essential. The No.20 could deliver 250 watts into 4 ohms without flinching, maintaining voltage stability even during orchestral crescendos or bass drops. Other amps would compress or clip; the No.20 just kept going, like a steamroller over gravel.
Industrial-grade build and thermal management: The chassis wasn’t just for show. Its 95-pound mass included thick aluminum side panels that acted as both structural rigidity and heat sinks. The internal layout was obsessive—short signal paths, star grounding, and point-to-point wiring minimized interference. And unlike some amps that ran hot enough to cook eggs, the No.20’s thermal design kept things stable, even during marathon listening sessions. It wasn’t just built to last; it was built to perform under duress.

Historical Context

The mid-to-late 1980s were a battleground for high-end audio. Tube amps still had their loyalists, but solid-state was making a serious play for fidelity and reliability. The Mark Levinson No.12 was the No.20's predecessor, and it had already set a high bar with its balanced design and clean output. But the No.12 was more of a refinement. The No.20 arrived as digital recording was gaining ground, and engineers needed amplifiers that could keep up with early CD masters. Its 10 Hz to 100 kHz frequency response stretched well beyond the range of human hearing, so even the fastest transients in digital audio were preserved.

It had stiff competition. The Krell KSA-200, produced from 1985 to 1989, was its most famous rival, with similar power, price, and prestige. Krell went with high feedback and high gain. Mark Levinson went the opposite direction. The No.20 was less about brute force and more about control, like comparing a Formula 1 car to a muscle car. Both are fast, but one is engineered for precision. By 1990, the Mark Levinson No.21 would succeed it, adding dual-mono construction and even more refinement.

Collectibility & Value

Today, the Mark Levinson No.20 is rare and very desirable. Fewer than 1,500 units were reportedly produced during its four-year run, and many have been retired, modified, or lost to capacitor decay. On the secondary market in 2025, a fully functional, well-maintained No.20 commands between $8,000 and $15,000, sometimes more if it's a No.20.5 variant with the upgraded power supply. Its 120 dB signal-to-noise ratio and 50 V/µs slew rate remain impressive even by today's standards.

Buying one takes some care. The capacitors in the power supply are now nearly 40 years old. Even if they haven't failed, they're likely degraded, which can mean hum, reduced dynamics, or catastrophic failure. The output transistors can also degrade over time, especially if the amp was run hard or poorly ventilated. A No.20 in mint condition should have been professionally recapped and tested. Look for service records, original packaging (a unicorn), and ideally a history of studio or professional use. These units were often better maintained than those in home systems.