Mark Levinson No.436 monoblock power amplifier:
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Circuitry
The No.436 shares many design features with the dual-mono amplifiers in Levinson's 300 series. This includes robust, low-impedance power supplies and balanced circuit technology derived from the Mark Levinson No.33 and No.33H monoblocks. A soft-clipping circuit reduces the audible effects of amplifier clipping or overload. A special turn-on circuit prevents sudden thumps and damage to components from the current inrush as the power supply's large filter capacitors charge.

All sensitive voltage-gain stages are fully balanced and independently regulated. Adaptively biased output stages give the No.436 many of the benefits of class-A operation without its having to dissipate huge amounts of heat. The No.436 includes S-series printed-circuit boards made with Arlon 25N composite, as in the Reference No.32 preamplifier. Arlon 25N gives PCBs a lower, more stable dielectric constant, said to result in better electrical isolation of circuit stages and better sound.

The power supply is dominated by a high-capacity (2372VA), low-noise toroidal transformer. Four large, triple-bypassed, low equivalent-series-resistance electrolytic filter capacitors provide a total of 80,000µF of energy storage. Madrigal uses heavy bus bars of oxygen-free copper and high-frequency power-supply bypass components to lower the No.436's power-supply impedance. Its power supply allows the No.436 to act as a voltage source, doubling the power every time the impedance load is halved—assuming your electrical circuitry will support the current flow. The No.436 can draw 25 amps at 120V from the wall when driving a 2 ohm load to its full power rating of 1400W.

The output stage has eight matched, complementary pairs of TO-3P bipolar output power transistors, these clamped to the heatsinks with an aluminum bar. This stage runs at relatively low temperatures due to the wide spacing of output transistors along the current-gain circuit board, and to the internal heatsinks.

The No.436 includes extensive protection from internal or external component failure. Fault conditions monitored include the presence of DC at the output, corrected by servos up to ±1V of DC offset. Thermal sensors switch off the No.436 when the heatsink temperature exceeds 85 degrees C. Excessive current draw, such as a short across the speaker terminals, or abnormal AC line voltages—ie, outside the 108-132V range on a 120V line—turns off the amplifier. Other switches, located inside each transformer housing, disconnect power if the transformer overheats. Soft-clip circuits prevent the output devices from saturating, preventing the high-energy, high-frequency ringing artifacts generated by hard-clipped output transistors from reaching and damaging loudspeakers.

The No.436 amplifier has Sherman-tank construction, an overkill power supply, and the best components money can buy, and its simpler internal construction has eliminated the time-consuming disassembly required to replace internal components of the 300-series amplifiers (footnote 1) It comes with a five-year, nontransferable warranty, but it's built to last a lifetime.

Setup
My listening area is a lightly damped, 5400ft³ room 26' long and 13' wide, with a 12' semi-cathedral ceiling. One end of the room opens onto a 25' by 15' kitchen through an 8' by 4' doorway. I set the No.436s behind the speakers, which were placed 5' from the back wall and 5' from either side wall. Each amp was placed in the middle of a stack of amplifiers, to approximate a closed-in rack setup. Even so, I never heard the fans come on during my long listening sessions.

I attached the spade lugs for the Pure Silver Cable speaker cable to the No.436s' speaker binding posts, which are widely spaced to meet the European CE regulations. I tightened the connections between speaker cable and amplifier using the large, curved wing nuts attached to the posts.

The No.436's turn-on sequence is simpler than the No.334's. The No.436 has four operating states, and Off. The Power pushbutton, which connects the amplifier to the AC mains, is on the front panel (the No.334's was on the rear). Pushing this puts the amplifier into Sleep mode and turns on the "small" power supply for its control circuits, and makes the front-panel LED glow steadily but dimly.

The No.436 is put into Standby mode by pressing a larger front-panel button, labeled Standby. This charges the main power supply and stabilizes the amplifier circuits, draws as much as 100W, and makes the front-panel LED blink slowly. After two seconds, or two blinks, a second push of Standby toggles the amplifier into On mode, producing a bright, steady glow from the LED. To put the amplifier back to Sleep, press Standby steadily for two seconds.

Sound
Listening to the No.436 was an unusual pleasure. It provided the same open, detailed, lush, sumptuous, warm sonic signature I associate with the No.334, as well as the same appealing midbass punch and deep-bass management. This bass authority complemented my Quad ESL-989 speakers, opening up their midrange. The No.436s delivered the same punchy, well-defined deep notes through the Revel Salons as when those speakers were driven by the Bryston 14B-SST.