Reference

Sidebar 2: DIY Monitoring

Inquisitive readers may like to hear what kind of garbage resides in their amplifiers' rails. Using an old AC-coupled power amplifier and speaker as a monitoring system, hook this amplifier's input ground to your hi-fi amplifier's central ground point (usually the 0V busbar between the reservoir capacitors). As you want to hear the AC signal on the rail, make sure that the DC voltage (which can be up to 100V) will be safely blocked. Connect a 100V, 100µF electrolytic in series with the hot input lead of the monitor amplifier, oriented so that the positive side of the capacitor is connected to the test amplifier's positive supply rail; ie, the positive terminal of the reservoir capacitor which isn't grounded. If you cannot reliably identify these parts, do not attempt this test!

Switch on the monitor amp first, but disconnect the monitor speaker. With both amplifiers switched on, reconnect the monitor (ideally placed outside the listening room) and play music through your hi-fi amp, which should be hooked up to your speakers in the normal way. On the monitor, unless you have a perfect amplifier, you will hear a rather unpleasant mixture of hum and buzz, with highly distorted music in the background.

The rails you are listening to are only displaced from the amplifier's output by the output device or devices.—Ben Duncan

Postscript: Harmonic Convergence in 2019

This article is one in a war of words of over 40 years, to show just how wrong—and bovine!—the hardline objectivist "sonic denialists" have been. Since 1992, a great deal more has been shown and proven (footnote 1) where the listeners'—the people's—score is 1, and naysayers 0. Some 20 years ago, Cyril Bateman discovered how to measure the ugly distortions in capacitors, previously scathingly denied by hard-line objectivists like Douglas Self (footnote 2).

Nowadays, one can read accounts of the Rauch amplifiers' sonics in the "Speakerplans" PA-users forum, where the DVT-50 appears under topic titles like "Are PA amps Hi-Fi?" and "Best sounding amp?" Tellingly, Bateman's work showed how using capacitors in a particular, niche way will minimize their distortion. Exactly what's inside the Rauch amplifiers, designed 20 years earlier. Also in my AMP-01 main-frame/back-plane preamplifier design, described in the May, June, July, August, September, October, and November 1984 issues of Hi-Fi News (footnote 3), in which I'd started using back-to-back Elcaps in my designs.

In the years before 1992, deep spectrum analysis was barely available to the poorly resourced audio industry. It was exotic equipment, complex, large, heavy yet insanely delicate, that mainly covered radio frequencies and models with enough dynamic range for hi-fi, was kit that only government and military-industrial contractors could afford.

Frosty January '87, an early Audio Precision test set arrived at the Rauch factory—the second UK user, after the BBC. The AP System One swept, and swept the board for regular THD+N percentage measurement (footnote 4). By 1990, my lab was equipped with the Dual-Domain DSP option, which created a spectrum analyzer, inside a machine already made for serious audio testing, ie, with robust and balanced connections—what even today's "house-priced" RF analysers and also toylike soundcard types both omit. As with these, harmonics could be shown as discrete spikes. But the AP's DSP also allowed plotting of harmonics against frequency and level. As above. Making raw harmonic information easier to grasp. Yet this way of presenting the picture appears to remain rare, years on.

I first read about the importance of harmonic structure in "Amplifier Musicality," an article by Jean Hiraga in the March 1977 issue of Hi-Fi News. In 1978, my console designer neighbor Harry Day showed me work by Russ Hamm, a recording engineer, about varied harmonic structures in recording equipment, and where the musical qualities were identified, and related to instruments.

In my 1996 world-reference hardback book High Performance Audio Power Amplifiers, I cite articles from Wireless World going back more than 70 years, where the need to consider harmonic distortion from a musical perspective is grasped. The Radio Designer's Handbook, a compendium from 60+ years ago, charts the musicality of harmonics up to the 20th. Is knowledge is regressing?

A difficulty with harmonic structures, is that they're harder to judge. But as with music, patterns can resolve. Between 1997 and 2000, I tested over 120 amplifiers using the Audio Precision System One Dual Domain with listening help from the musically adept ears of Norma Lewis, and spotted something about varied equipments' distortion hitherto undocumented, and came up with a single figure of merit. Simplicity with corroboration. This development was related in my then column in Hi-Fi News.

As for power supply noise rejection, the continuing widespread market for power conditioners may speak for itself.—Ben Duncan (footnote 5)

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Footnote 1: The professor removes his right sandal and thrashes it violently on the desk, awakening listeners with a pure transient.

Footnote 2: From the 1970s through the 1990s. Douglas Self has been denying in print that capacitors can affect sonic quality. However, in light of Bateman's hard measured proofs of distortion in capacitors in 2001–2003, which backed up nearly all the things audiophiles had heard as to best capacitor types, he nowadays brazenly mentions in his books capacitor choice, for example, and usage, in particular, to avoid distortion—a design aspect, naturally he has always known about all along. (Sarcasm Knob set at 13.) This is a classic strategy—stone-walling; denial; scathing criticism; but then making out he invented it all along.

Footnote 3: I still have the example of the single-chassis version of Ben's AMP-01 that I used as my reference preamplifier before purchasing an Audio Research SP-10 in 1985. I should retrieve it from my storage unit and give it a listen.—John Atkinson

Footnote 4: Stereophile purchased an Audio Precision System One in 1989 and had it upgraded to Dual Domain status a year later. I used it until it was replaced by an Audio Precision SYS2722 at the end of 2007.—John Atkinson

Footnote 5: Ben Duncan's job description ranges though analog electronics engineer, product designer, inventor and research scientist, bringing musical quality to the tribal sonic worlds of recording studios, live stages, festivals and dance venues, thro' to serious hi-fi.