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Lamm ML2.1 monoblock power amplifier Measurements

Sidebar 3: Measurements

Following Vladimir Lamm's instructions, I let the ML2.1 run for an hour or so before I checked the output tube's plate voltage and current. While the voltage was correct at 175V DC, the current was a little high at 0.35A. I adjusted it to read exactly 310mA, as recommended in the excellent owner's manual (one of the best I have encountered). All measurements were made using the unbalanced RCA input, as the XLR is provided as a convenience only. (Pin 2 parallels the RCA jack, pin 3 is connected to ground.)

As expected, the ML2.1's voltage gain dropped as…

Lamm ML2.1 monoblock power amplifier Follow-Up, September 2005

Art Dudley wrote again about the Lamm ML2.1 in September 2005 (Vol.28 No.9):

My parents' first house, which they bought three years after I was born, cost $11,000—a factoid I've always been able to cough up at will, no matter how many breakfasts I forget. My parents' second home, which had two floors and a coal-burning furnace, cost $13,000. Some years later I spent $900 on the first car I bought (a Plymouth Duster); many years later I spent a little less than $22,000 on my most recent one (a Subaru Forester). I still have my first guitar amplifier (a 1966 Fender Vibro-Champ, bought as a…

Listening #9

In the town where I grew up there were two places to buy records: a family-owned department store and the local Woolworth's, both long gone. The first record I ever bought, the 45rpm single of Roger Miller's "King of the Road," came from the former in 1965. I was 11 years old.

Those stores and the 7" records they sold got a lot of attention from me and my friends, but we didn't start buying LPs until a few years later. For one thing, we couldn't afford albums, which cost three dollars and change—a little less for mono when the choice existed—as opposed to 99 cents for singles. For…

Listening #9 Page 2

The final blow was one that Procol delivered themselves: a complete and utter absence of visual appeal. Bandmembers appeared in concert and on TV dressed in fringed boots, Mandarin caps, and cheap-looking satin tunics and capes, looking less like pop stars than medieval Chinamen from outer space. Moreover, Procol Harum shows weren't shows at all, and notwithstanding the group's superb musicianship—"Repent, Walpurgis," a downtempo instrumental by Fisher that sounded like nothing else in pop, seldom failed to get an ovation—they didn't give the audience a whole lot to look at. Fellow…

Listening #9 Page 3

It took a while to locate the production master for the single—the original four-track tapes haven't surfaced since 1967, and are presumed forever lost—but along the way someone turned up a box from Advision Sound Studios in London, dated "April 1967" and marked, simply, "Whiter Shade of Pale plus takes." (Charmingly, the label on the box credits someone named Procol Harrian.) Rather than a mixed and EQ'd production master, the box contained an original four-track tape. Careful playback revealed the contents to be three different, unmixed recordings of the song, each slightly different from…

Super Audio CD: The Rich Report

Although Philips invented the Compact Disc, it was only when Sony got involved in the early 1980s that it was decided—at the prompting of conductor Herbert von Karajan, a close friend of Sony's then-president Akio Morita—that the CD should have a long enough playing time to fit Beethoven's Ninth Symphony on a single disc (footnote 1). Even if the conductor was using very slow tempos, and even given the minimum pit size and track pitch printable at the time, the 16-bit data and 44.1kHz sampling rate they settled on gave them a little margin.

From the beginning, it was pointed out that…

Super Audio CD: The Rich Report Page 2

It should also be noted that 1-bit delta-sigma bitstreams are very sensitive to such analog issues as clock jitter, edge speeds, and folding of the very-high-energy out-of-band noise into the baseband. This gives rise to more tones and oscillations. The multi-level approach used in all high-performance delta-sigma DACs these days does reduce this problem, however.

In delta-sigma DAC designs the trend has been to go to 20 or more levels for the internal DAC instead of one level, and up to 18-bit linearity (Analog Devices, Crystal, and even single Bitstream inventor Philips Semiconductor…

Super Audio CD: The Rich Report Page 3

Making the inherent data inefficiency of a delta-sigma datastream worse is the fact that lossless coding is less effective than the MLP used in the PCM-based DVD-A. Because of all the high-frequency energy in the stream (energy that would be rejected by the decimators used in a PCM-based system), the DSD data are less correlated and less susceptible to efficient packing.

Why would Sony and Philips introduce a medium that, while offering higher resolution than CD, uses an inefficient coding scheme, needs great care to avoid stability problems with that coding, and requires analog low-pass…

Super Audio CD: The Rich Report Page 4

Why am I skeptical about the "simple signal path" explanation? In addition to the practical problems of converting an SACD datastream directly to analog that I discussed above, the proposed simplified signal path assumes no signal processing between the digital tape recorder and the SACD mastering process. Even something like mixing a multitrack recording—mixing can occur directly on a delta-sigma stream—results in a multibit stream, even if the mix occurs one-to-one. While it is possible to equalize and even add reverb in the delta-sigma domain, these again result in multibit streams. Once…

Super Audio CD: The Rich Report References, Delta-Sigma Converters

Sidebar 1: References, Delta-Sigma Converters

S. Norsworthy, R. Schreier, G. Temes, eds., Delta-Sigma Data Converters: Theory, Design, and Simulation, IEEE Press, 1997.

After 15 years of very active development that was covered only in journal articles and the occasional book chapter, here are the seminal texts from all the leaders in the field. Each chapter of Delta-Sigma Data Converters includes extensive references that I do not restate here.

Chapter 1 introduces the topic, including pattern noise, dead zones, limit cycles, and dynamic-range limitations. High-order…