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…
Sidebar: Doppler and DiAural
Although the initial fuss that accompanied Ray Kimber's 1999 launch of DiAural—the proprietary speaker-crossover technology developed by Eric Alexander—has died down, the fact remains that it was and still is promoted as a means of canceling the Doppler distortion introduced by microphones: "Doppler Decoding," in DiAuralspeak. To my knowledge, however, this claim has never been challenged in the audio press. Although DiAural's two patents (US 6,115,475 and 6,310,959 B1, copies of which you can download from the US Patent Office make no mention of Doppler…
Keith Howard returned to DiAural in January 2005 (Vol.28 No.1):
When I wrote the "Doppler and DiAural" sidebar for my recent feature about Doppler distortion in loudspeakers ("Red Shift," November 2004, p.67), I fully expected a retort from DiAural founder Ray Kimber, of Kimber Kable. In the event, both he and Eric Alexander, the originator of DiAural's crossover design concept, took up their pens to point out to me that the Doppler decoding explanation with which DiAural was launched had been withdrawn before my article was published.
I wish, of course, that I had known this…
