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…
The No.436 produced fast, solid bass with great pitch definition, and had no problems reproducing the solid, sustained pedal chords of the Lay Family Concert Organ during John Rutter's "The Lord is My Light and My Salvation" (CD, Reference RR-57CD). The explosive plucked bass and synthesizer notes that open "Something's Wrong," from the My Cousin Vinny soundtrack (CD, Varèse Sarabande VSD-5364), were stunning. Terry Dorsey's "Ascent," from Time Warp (CD, Telarc CD-80106), rumbled through my listening room. Each change in synthesizer pitch was clear and authoritative in "Behind the Veil,"…
Sidebar 1: Specifications Description: Solid-state monoblock power amplifier with one pair Madrigal speaker binding posts, one 3-pin XLR balanced input, two 1/8" minijacks for remote turn-on, one RS-232 port on RJ-11, two Mark Levinson communication ports on RJ-45, and two PHAST communications ports on RJ-45. Rated power output (20Hz-20kHz, <0.3%. THD, FTC): 350Wpc into 8 ohms (25.4dBW), 700W minimum continuous into 4 ohms (25.4dBW), 1400W minimum continuous RMS power at 2 ohms (25.4dBW). Frequency response: 20Hz-20kHz, ±0.2dB. Output impedance: ±0.05 ohm, 20Hz-20kHz. S/N Ratio:…
Sidebar 2: Associated Equipment Analog source: Linn Sondek LP12/Lingo turntable, Linn Ittok tonearm, Spectral moving-coil cartridge.
Digital source: Krell KRC-28 CD transport, Sony SCD-C555ES multichannel SACD player.
FM tuners: Day-Sequerra FM Reference Classic, Magnum Dynalab MD-102 with Model 205 Sleuth RF amplifier, Fanfare FT-1A, McIntosh MR-78, Sony ST-5000.
Preamplification: Krell KCT, Sony TA-P9000ES, Mark Levinson ML-7A with L3A moving-coil phono stage; Margulis phono preamplifier; Duntech MX 10 moving-coil preamplifier.
Power amplifiers: Krell FPB 600c; Bryston 7B-…
Sidebar 3: Measurements One difference between a modestly priced amplifier and something like the Mark Levinson No.436 is that the latter will run forever without overheating. Following the usual preconditioning period of driving one-third power into 8 ohms for one hour, the No.436's internal heatsinks were too hot to touch, but its cooling fan hadn't come on, and its chassis was merely warm.
The voltage gain was the same through the unbalanced and balanced inputs, at 26.75dB into 8 ohms. (Pins 1 and 3 of the balanced XLR jack were shorted with the supplied jumper when the…
Results
The test procedure was as follows: an FFT-derived spectral analysis was performed on the processor's clock jitter (the LIMD output) when the processor was driven by the digital code representing a 1kHz sinewave at six input levels ranging from 0dBFS to -90dBFS. The FFT plots show energy vs frequency. The spectral analysis was repeated with the processor under test driven by digital silence (all data words are zero), a 1kHz squarewave, and a 10kHz sinewave at 0dBFS (full scale). The LIMD output was then connected to a true-RMS voltmeter and the jitter voltage measured with all…
Despite my negative feelings about its sound quality, the Vimak DS-2000 (reviewed last month) had astonishingly low levels of jitter: just 34.8ps compared with their specified 50ps. However, although the jitter might be thought to be random in nature, there are a number of discrete low-amplitude spectral lines visible below 6kHz (fig.16). These measurements were made right at the DAC's word-clock pin. Interestingly, the word clock was even cleaner when measured where it enters the analog board, indicating that these discrete components are introduced after the input receiver. Compare fig.16…
Sidebar 1: The Timing Problem
For the mathematically inclined, the signal/noise ratio (SNR) in a digital system is affected by time-base jitter in the following manner:
SNR = 20 log10(2 T PI F Square Root(2 F0/FS))
where: T = RMS jitter
PI = 3.1416
F = signal frequency
F0 = bandwidth of noise measurement (20kHz)
FS = sampling frequency (352,800Hz for 8x oversampling)—Robert Harley
Sidebar 2: Politics
When John Atkinson and I first learned that the Meitner/Museatex LIM Detector was available for purchase, we were tremendously excited by the possibility of using it to measure jitter in digital audio processors and report the results in Stereophile. We were, however, aware of the political implications of buying a test-measurement system from a manufacturer who makes digital processors and competes with other manufacturers of digital processors. It is possible for a manufacturer to devise a test of questionable worth on which his product performs well but makes other…
The Jitter Game Revisited, April 1993 (Vol.16 No.4):
This "Follow-Up" also provides an opportunity to clarify a perplexing issue raised in the January jitter article. From those measurements, it would appear that processors with single-bit converters have much lower jitter than the more common 8x-oversampling units that use multi-bit DACs. Indeed, 1-bit converters typically have only a few picoseconds of jitter, rather than several hundreds of picoseconds or even several nanoseconds for multi-bit converters. Is the jitter performance of 1-bit machines intrinsically lower, thus "better…
