REFERENCES
[1] M. Colloms, High Performance Loudspeakers, Fourth Edition, pp.391-395 (John Wiley & Sons, 1991). [2] F.E. Toole, "Listening Tests—Turning Opinion into Fact," presented at the 69th Convention of the Audio Engineering Society (1981 May). Preprint 1766. J. Aud. Eng. Soc. Vol.33, pp.439-440 (1982 June).
[3] F.E. Toole, "Subjective Measurements of Loudspeaker Sound Quality and Listener Performance," J. Aud. Eng. Soc. Vol.33, pp.9-12 (1985 January/February).
[4] Perception of Reproduced Sound 1987, Symposium Proceedings edited by S. Bech & O. Juhl…
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'…
In the third voltage-gain stage, the signals are converted to a pair of SE signals of equal amplitude and opposite polarity (balanced, as we know it). Each of these signals then moves on to its current gain stage. Forty output devices (two sets of 10 complementary pairs) are used in the output stage. This means the output terminals do not reference ground at all.
Like its big brother and the rest of the 300 series amplifiers, the No.33H is equipped with Madrigal's Adaptive Biasing system. This maintains a state of equilibrium by referencing both the instantaneous voltage and the…
High Society
This, of course, forces the question: How do the Mark Levinson No.33H monoblocks compare to the Krell Full Power Balanced 600, Stereophile's joint Amplification Product of the Year for 1997? After all, Martin Colloms went so far in his review last April as to claim that the Krell so rewrote the book on amplification as to require a total reexamination of Class A power amplifiers in Stereophile's "Recommended Components." I'm not sure I'd go that far, but Martin is essentially correct: Compared to the Krell, almost everything else sounds broken. Directly comparing the FPB…
Specifications
Description:Solid-state monoblock power amplifier. Rated continuous-power outputs: 150W into 8 ohms (21.8dBW), 300W into 4 ohms (21.8dBW), 600W into 2 ohms (21.8dBW), 1200W into 1 ohm (21.8dBW). Frequency response: 20Hz-20kHz, 0.5% THD. S/N ratio: better than 80dB (ref. 1W), better than 105dB (ref. full output). Input impedance: 100k ohms balanced, 50k ohms unbalanced. Output impedance: 0.05 ohms, 20Hz-20kHz. Damping factor: greater than 800 at 20Hz. Input sensitivity: 130mV for 2.83V output, 1.59V for full-rated output. Voltage gain: 26.8dB. Typical power consumption: 540W…
Measurements
After a one-hour preconditioning period driving 1kHz at one-third power into 8 ohms (which maximally thermally stresses an amplifier with a class-B output stage), the No.33H's vertical heatsink arrays were warm, but not excessively so. The amplifier was non-inverting via the RCA jack or via the XLR with pin 2 wired "hot." Its input impedance was to specification at 49.6k ohms (unbalanced) or 104k ohms (balanced). The sensitivity was also as specified, 130mV resulting in an output voltage of 2.838V into 8 ohms (a voltage gain of 26.8dB). The measured output impedance was…
At a higher 50W level into 8 ohms, the residual distortion (fig.4) was primarily third-harmonic; though at 0.0045%, this is probably of academic interest only. Lowering the load impedance to 2 ohms and keeping the output voltage constant, resulting in 200W dissipation in the load, brought up the level of second-harmonic distortion, as is shown in fig.5.
Fig.4 Mark Levinson No.33H, 1kHz waveform at 50W into 8 ohms (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).
Fig.5 Mark Levinson No.33H, 1kHz waveform at 200W into 2 ohms (…
In the world of digital audio, jitter has been a focus of audiophile attention for well over a decade. It is blamed for many of the sonic ills of which CD and other digital media have been accused. But here's a puzzle: The major source of frequency intermodulation distortion in audio systems—the loudspeaker—has largely escaped such withering inquiry. Why?
Two reasons spring to mind. First, the common origin of these distortions is obscured by the fact that they go by different names and are quantified differently. Whereas frequency intermodulation (FIM) in the digital context is called…
Prior art
Interest in Doppler distortion began in 1943, with the publication of a paper by two RCA engineers, G.L. Beers and H. Belar, which was the first to identify and quantify this distortion mechanism (footnote 1). Interest in the subjective effects of Doppler distortion intensified in the 1960s with the work of James Moir in the UK (footnote 2) and Paul Klipsch in the US (footnote 3), both of whom concluded that it had a significant effect on speaker sound. But these findings relied in major part on comparisons of speakers with different levels of Doppler distortion, the…
Even when this degree of care is taken over interpolation accuracy and filtering, there remains the possibility that some subtle signal degradation will occur, not least because of the addition of TPDF (Triangular Probability Density Function) dither, prior to requantizing the processed signal, raises the noise floor. To account for this, I included in the software a "Generate Reference" option, which applies the same processing steps without the addition of frequency modulation, and generates all output samples from points midway between interpolated samples to ensure that the maximum…
