Mark Levinson No.33H monoblock power amplifier
By Wes Phillips   •   January, 1998 Chances are you've never seen an amplifier quite like the Mark Levinson No.33H. That's because there's only one other amp that's anything like it: the Mark Levinson No.33, upon which it's based. Both amps are more tall than broad, looking almost as though they're resting on their ends; heatsinks cluster around their side-panels. In the city of the High End, the No.33 and No.33H are skyscrapers standing tall above the warehouses.

When Madrigal first unveiled the No.33, they were drawing a line in the sand. "This is everything we know about building amplifiers," they said. But they weren't prepared for the public's response to their No.33 Reference statement—at $33,000/pair, they figured they'd sell a few a month, but that there could never be that much demand for a heavy (well over 200 lbs), massive, 300Wpc monoblock. They were wrong. "The response was overwhelming," said Jon Herron, head of product development at Madrigal.

C'mon, Jon—"overwhelming"?

"We often had to carry No.33 back-orders from one month to the next. The labor involved in building each amplifier is prodigious, and the space necessary for all of the major subassemblies during the final assembly and testing is enormous. We are therefore limited to building a maximum of between 10 and 15 pairs of these amplifiers per month. We do have other products to build."

Realizing that many audiophiles didn't need all the power offered by the No.33, Madrigal set out to design a half-powered version, the No.33H, which puts out 150W into 8 ohms (the power successively doubling into 4 ohms, 2 ohms, and 1 ohm). But, Madrigal is quick to point out, although the No.33H is based on the No.33, it is not a Reference product. Just as on Highlander—there can only be one.

High power
Make no mistake, the No.33H doesn't look—or act—like a scaled-down anything. It's huge (11" W by 18.5" H by 22.88" D) and heavy (175 lbs each). And when Madrigal lists its output power, they add an ominous-sounding "assuming the wall outlet is up to the task of supplying all that power." Wow.

Let me put the '33H's stupefying power capabilities in perspective: Each monoblock employs four 60,000µF capacitors, for a total of over ¼ Farad of capacitance. (By contrast, the 200Wpc No.332 uses a pair of 50,000µF capacitors per channel.)

In fact, the power supply of the '33H is a good place to start examining the amp. It uses two independent, bipolar power supplies in order to maintain the fully balanced nature of the amp from input to output. These come off a single, Madrigal-designed 3.417kVA transformer, utilizing multiple taps to maintain the symmetry of the two bipolar supplies. (Madrigal points out that the transformer VA output of the '33H is 70% of that for the No.33 because the voltage swing at half-power is actually 70% of that found in the '33.)

While the No.33 uses two 2.5kVA transformers, that's a matter of practicality, not necessity. Since the '33H is a monophonic amplifier, symmetry for the inverting and noninverting sides of the same signal is assured.

The '33H also employs an AC regeneration system for the input and driver stages. This drains off a portion of the ± DC power from the main supply, powering an oscillator circuit that generates pure-sinewave AC. This uncontaminated AC is rectified, filtered, and regulated. You could say the heart of the amplifier is a mini power station designed to deliver AC of uncompromised purity.

Incoming signal from the preamplifier is received using proprietary topology—again developed for the No.33—that eliminates the standard feedback point on the inverting leg of the first-stage differential amplifier. This means the two sides are truly balanced from the start. Each leg of the signal is handled differentially. The two balanced voltage-gain stages, running side by side, are essentially "double"-balanced. Even single-ended inputs are converted to balanced in the first voltage gain stage, and are run "double"-balanced in the second.