The output impedance of the D-105u from its fixed outputs was considerably higher than spec at 1200 ohms, though the variable outputs offered a lower source value of 645 ohms. Long cables should be avoided when the player is used from its fixed outputs, though the lower impedance of the variable outputs is sensible when the player is fed straight to the power amplifier. The maximum output level was 2.11V from either set of outputs, while the output was polarity-correct from both outputs, as shown by the linear-phase impulse response (fig.1). Channel separation was…
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This photograph of a classic 1960s HP scope (capable of a sharper and brighter trace than today's equipment) at Ben Duncan Research Labs shows a sinewave emerging from an innovative class of solid-state analog amplifiers, developed with Jerry Mead (founder of much-loved Rauch and Otis amplifier brands, also a record producer and drummer). The residual harmonic is so low—around 0.0001% even while delivering several amperes and tens of volts—that it contains stochastic noise, and fancy equipment isn't needed to see that Voila! we have just the 2nd harmonic. No 3rd, no 4th even. The electronics…
Conventional acoustic and audio knowledge has little enough to say about the sonic effects of harmonics when they're gross (ie, 50% to 0.5% of the fundamental). At lower levels, almost nothing is documented, and extrapolation of the high-level effects would seem presumptuous. I have witnessed experiments in which the effects of introducing at below –95dB a spray of harmonics, including the seventh, ninth, and eleventh, by loading-down an IC op-amp, are: a) perfectly audible, but b) perceived more as a dulling loss of detail and air than as dissonant in the usual sense of "anti-melodic" or…
Sidebar 1: References & Further Reading
+[1] Jim Williams, Analog Circuit Design—Art, Science & Personalities. Butterworth-Heinemann, ISBN 0-7506-9166-2.
[2] Ben Duncan, "Evaluating Audio Op-Amps, Part 1." Studio Sound, July 1990.
[3] Ben Duncan, "Black Box." Hi-Fi News & Record Review, June 2000.
[4] David Bohm, Wholeness and the Implicate Order. Ark Books, 1995, ISBN 0-415-11966-9.
[5] M. Talbot, The Holographic Universe. Grafton Press, 1991; HarperCollins, 1996.
[6] Ben Duncan, "Evaluating Audio Op-Amps, Part 3." Studio Sound,…
Sidebar 2: Integrated Circuits
In 1950, the US Navy's Bureau of Aeronautics needed to build complex, reliable, serviceable weapons systems, but were hampered in this by the tube technology of the time. They thus set up a study of automated tube circuit assembly. The resulting prefabricated circuits were fine, but by the time they were ready, the crucial development of making transistors reliably and cheaply by making them "epitaxially"—ie, by growing doped layers on crystals rather than by hit-or-miss mechanical assembly—made several million dollars' worth of fine tube-based engineering…
Sidebar 3: Hard-Line Objectivists
"Hard-Line Objectivists" is my name for certain self-appointed Czars of audio equipment design. They think that the senses of humans, even skilled audio professionals, should never be relied on in matters of audio equipment assessment using music; that only test gear should decide; that audio equipment is perfect and sounds "blameless," provided it meets highly limited tests; that only a steady sinewave is required to discover all that is knowable about audio equipment; that capacitor, resistor, thermal, and dynamic distortions do not exist because they…
Sidebar 4: Acid Tests for Musically Refined Electronics
My colleagues have noticed over the years that, with refined audio electronics built to be musically satisfying,
The worst room acoustics can be conquered or at least greatly ameliorated.
Music can be played effortlessly at extreme SPLs without ear pain or stress (see my "Earlash" in the June 1995 Studio Sound).
Threshold shift is absent—when a 130dB peak SPL sound stops, birdsong is as audible as if nothing loud had happened.
In people with previously damaged ears, tinnitus is not triggered…
Postscript August 2020
As a band plays a lazy jazz-blues in the corner, and everyone has gotten refreshed with eine kaltes Bier, the professor's central-European audience are warned that a small spectral leakage across multi-channel ICs is developed into a far greater and wider kind of audioland X-contamination, as outlined below.
Another threat is the Ring of 3, an op-amp "state variable" topology used in posh equalizers and crossovers. As with the innards of NFB amplifier stages, while low distortion on the outside lures use, voltage waveforms inside the ring aren't pretty.…
Sidebar 5: Digital Perversions
Widely unrecognized, is that class-D amplifiers, depending on voltage-challenged switching-MOSFETs, are so compromised for voltage swing, that almost all rely on bridging to deliver power levels into 8 ohms that analog amplifiers managed 40 years ago. Technological retrogression sits in plain sight.
Meantime, bad digital can make the most unnatural harmonics of all. The fifth-and-a-half has been observed. There are also sub-harmonics: Fit only for horror movies. Worse, modern test instruments hide such inconvenient data, as sub-educated modern "…
40 years ago—"is the English way"...
It's the 8th of August 1980 and Ben Duncan (top left), hand resting on his famous investigative clipboard, is leaning against the Pink Floyd The Wall concerts' huge front-of-house mixing setup, inside Earls Court, West London. The crew are getting ready for sound-check. It's the second night of a world tour, and there have been some teething problems. In front of the alleyway of racked outboard equipment, are an amazing 105 channels made with joined-up English Midas Pro4 consoles. These were…