TAS Legacy: Audible Illusions Modulus Preamplifier

Equipment report
Solid-state preamplifiers
TAS Legacy: Audible Illusions Modulus Preamplifier

In the late 1970s, three talented Silicon Valley engineers—Bruce Moore, Tom Taylor, and Alan Priestly—formed Audible Illusions. Having already earned a reputation as a “tube wiz” from his noteworthy preamplifier designs for Precision Fidelity and Paragon, Moore teamed with Taylor to create the original Audible Illusions Dual Mono, Uranus 11, and Mini-Mite preamps. The diminutive Mini-Mite 1 was minimal in its design, providing only a volume and balance control along with inputs for phono, tuner, and tape. Three tubes—one 12AX7 and two 6DJ8s—and a regulated power supply completed the picture. TAS reviewer Patrick Donleycott called the Mini-Mite ($339 for the kit version and $427 wired) “a real sleeper of a preamp,” and noted that it was “extremely easy to listen to for extended periods of time. Certainly, if you’re starting out on a budget, this might be the place to begin” [Issue 20]. This purist design served as an important foundation for the company’s progression to its most significant and popular series of preamplifiers, the Modulus.

Shortly after Bruce Moore’s departure, Audible Illusions’ head of sales Art Ferris took control of the company in 1983. He made a significant personal investment to redesign the preamplifiers, particularly to improve their reliability. For example, Audible Illusions was one of the first audio companies to incorporate automatic muting turn-on safety circuits. Under Ferris’ leadership, the company pursued “simpler, more elegant designs” stemming from Ferris’ interest in and familiarity with Japanese single-ended approaches.

The company’s new focus led to the Modulus 1 preamplifier, introduced in 1983 at $449. What distinguished the Modulus, besides its remarkable price, was the use of 6DJ8 dual-triode tubes, instead of 12AX7 tubes with cascode circuits, cathode followers, and negative feedback. The Modulus 2, with its complement of four dual-triode 6DJ8s—two for its built-in phonostage and two for its open-loop linestage—sold for $675. Separate volume controls (one for each channel) replaced its balance pot, and its linestage no longer shared a single 6DJ8. Not surprisingly, with each subsequent (and seemingly biennial) revision, the Modulus’ performance improved significantly.

Applying Audible Illusions’ “Simpler is Better” mantra, the Modulus preamplifier offered aspiring audiophiles a relatively low-cost entry into the high end. Key factors in the Modulus’ performance were its simple dual-mono signal path without any cathode followers and its paralleled-tube linestage. It also sported a sophisticated, low-impedance power supply, initially designed by Barry Streets, with further modifications by Sid Smith and John Curl. The low-noise phonostage, originally designed by Moore, was subsequently revised with the help of Sid Smith and Roger Modjeski. As its performance, features, parts-quality, and sophistication increased, so did its price: from $449 for the Modulus 1 to the Modulus 3B of today, starting at $3995.

According to Art Ferris, over 19,000 Modulus preamplifiers have been produced since 1983. “What makes our preamplifier designs so successful is the incorporation of modern technology and specially designed parts into these basic circuits. Our engineers understand the superior linearity of a quality vacuum-tube design. They also believe that these circuits must be kept simple with single gain stages and no error-correcting feedback. Add to this, ultra-fast low-impedance power supplies that can supply voltage to meet the demand of complex musical waveforms, and you have the beginnings of a great audio preamplifier.”

The Audible Illusions Modulus 3A preamplifier was recognized as one of the 12 most significant preamplifiers of all time by The Absolute Sound (Issue 223) and praised for “delivering reference-caliber sound quality at an affordable price point. It wasn’t just that it excelled in transient clarity and soundstage transparency; its textural liquidity was also a most satisfying testimonial to a classical tube heritage.” The Modulus 3B remains in limited production as of this writing.