MARK LEVINSON No20.5L

Commentary

Monaural power amplifier developed with improved sound quality based on No20L.

The main change from No20L to No20.5L is the improvement of the circuit and circuit elements from the input stage to the voltage amplification stage.
Also, taking advantage of the unique modular construction, it is realized by redesigning a single plug-in PC board (card module).

The power supply section is equipped with two large-capacity toroidal transformers of 600 VA and has a completely ± independent configuration. The electrolytic capacitor is connected in parallel with a high-quality polyethylene type with extremely low noise and excellent impedance characteristics. Moreover, a large-capacity and high-speed regulator circuit is adopted to control all stages of the power amplifier including the output stage.

AP-4 circuit board is used for input stage and amplification stage.
The voltage amplification stage consists of a 2-stage differential AC amplifier, the first stage consists of a differential circuit with NPN transistor, and the FET is cascode-connected. The second differential amplifier consists of an active broad based current mirror push-pull operation, the voltage amplification stage consists of a 3-stage Darlington configuration, the driver stage consists of triple push-pull, and the output stage consists of an 8-stage para-push-pull configuration.

As the power transistor, several candidates selected from all over the world were subjected to characteristic tests again, and the remaining ones were put on for a long time hearing test, and only one bipolar transistor was picked up.

The protection circuit is designed to eliminate relays, which can cause sound quality degradation, and to turn off the power in the event of an accident.

In addition to the highly reliable CAMAC terminal, the XLR (Canon) terminal is also available for balanced input.
In addition, the INVERTING terminal is mounted, and it is possible to bridge two units.

Upgrade service included replacement of AP-3 circuit board for No20L to AP-4 circuit board for No20.5L, replacement of power transistor set and replacement of front panel with model No20.5L (AP-3 circuit board, power transistor and front panel were Herman-certified).

Model Rating

Type	Monaural power amplifier
Circuit	Complimentary service push-pull circuit by pure class A operation at all stages
Rated output	400W (2 Ω) 200W (4 Ω) 100W (8 Ω, 20 Hz to 20 kHz, THD0.1% or less)
Input impedance	50k Ω
Pwer	100 VAC, 50Hz/60Hz
Power consumption	Approx. 500W
External dimensions	Width 483x Height 210x Depth 560 mm
Weight	33kg
Remarks	Upgrading from No20L to No20.5L Replacement of circuit boat and transistor (¥ 358,000) Front panel replacement (¥ 110,000)