AOM Logo June 1998

The Audible Illusions Modulus 3A
The Evolution of the Full-Function Preamplifier

Andrew Chasin

Combining the intractable components which comprise the typical audio circuit (capacitors, resistors, inductors, and the like) into a device which conveys the essence of the live musical experience is unquestionably as much art as it is science. The gifted engineer who lacks the open-mindedness to acknowledge the sonic limitations of his creations, no matter how well they may conform to the theoretical ideal, or the conviction and courage to say "black" when conventional wisdom dictates "white", will likely be unsuccessful in bridging the chasm from Faraday to Fauré. Indeed, there is empirical evidence to suggest that those audio designers with no formal training in electronics or engineering are equally (if not more) likely to create a superbly musical device, one capable of faithfully communicating much of live music's beauty, power and emotion.

And so it is with Audible Illusions' Art Ferris, a trained graphic artist turned electronics designer, thanks in no small part to the teachings of such industry luminaries as John Curl and Saul Marantz. Ferris, once the overseas marketing representative for Audible Illusions, took control of the company in the mid-eighties, at a time when product reliability and quality control were suspect. Through an obsessive commitment to product development and improvement, coupled to an uncompromisingly purist approach to high-end preamplifier design, Ferris has taken Audible Illusions' flagship product, the Modulus preamplifier, to new heights of quality, reliability and musicality.

Audible Illusions Modulus 3A

The Inside Story
The most recent incarnation of the Modulus preamplifier, the Modulus 3A, bears little internal resemblance to its predecessor, the Modulus 3, although externally it is virtually unchanged (save for the addition of green backlighting for the front panel control knobs). Significant changes have been made to the preamplifier's power supply, and the way in which power is distributed within the preamplifier itself. The 3A's larger power supply, said to be capable of even wider voltage swings than its predecessor, now contains a transformer manufactured in-house, replacing the externally-sourced unit employed in the Modulus 3, and thus eliminating a potential source of quality control problems. Unlike the Modulus 3, power to each of the 3A's seven sections is now fed from its own regulated supply. As in previous versions of the preamplifier, the power supply is housed externally, and is coupled electrically to the main unit via a non-detachable umbilical.

The already impressive array of mil-spec parts which were employed in the Modulus 3 (many of which were custom-made for Audible Illusions) has been further improved upon in the 3A, with judicious use of 1% resistors and custom polystyrene and polypropylene capacitors, all mounted on high quality double-sided star-grounded circuit boards. Close inspection of the 3A's innards reveals that a high degree of care and craftsmanship have gone into this product's design and assembly, far exceeding what would normally be expected at this price point.

Like the Modulus 3, the 3A utilizes a tubed line stage (one 6922 per channel) run in class A with no feedback or output cathode follower. While a cathode follower is often employed to lower the output impedance of a tubed preamplifier, Ferris' less-is-more approach foregoes such a circuit in favor of lower noise and reduced phase shift. Gone unchecked, the 3A's relatively high output impedance (1.2 kOhms) might have resulted in audible high-frequency rolloff if long cable runs were employed. Audible Illlusions minimizes the likelihood of such rolloff by running the 3A's tubes in parallel (thus halving their impedance), utilizing low-capacitance potentiometers, and increasing the preamplifier's current drive.

With its integral tubed phono stage (also utilizing one 6922 per channel), the Modulus 3A is an analogue lover's oasis in a desert of line-level only offerings. The tubed phono stage included with the 3A is only suitable for use with moving magnet or high-output moving-coil cartridges. Users of low-output moving coil cartridges may opt for the John Curl-designed gold phono board (so called because its circuit traces and ground plane are etched in gold), a solid-state high-gain stage said to be the close cousin of Curl's highly-respected Vendetta Research SCP-2. Combining the solid-state gold board and the tubed moving-magnet board results in a tube/solid-state hybrid phono stage capable of accepting cartridges with outputs between 0.1 and 0.7 mV. The gold phono board was installed in the review sample so as to provide adequate gain for the 0.4mV Benz-Micro MC Gold.

Although the 3A does not offer the same level of aesthetic or ergonomic refinement as some of its competitors - styling is somewhat retro, and even the most basic of remote controls is unavailable - its exterior fit and finish are, nonetheless, impressive. Encased in anodized aluminum, the low-profile main chassis features a ¼" thick rounded faceplate and a vented top-plate, each affixed with gold hex-head bolts. The 3A's repertoire of front panel controls includes a rotary-style input selector and tape monitor, dual stepped attenuators for independent control of left and right channel volume, a mute button, and a subsonic filter. All rotary controls are machined from aluminum and finished to the highest degree. Other features include a mono blend switch (essential for those who own recordings from the pre-stereo era) and a standby switch. Since the Modulus is intended to be left in standby mode when not in use (this mode designed to extend tube life by reducing tube voltage while keeping the filaments heated), no power on/off switch is provided. The rear of the main chassis features a pair of high-quality Teflon-dielectric RCA jacks for each of the 3A's six inputs (five line-level, one phono), as well as a grounding post. The chassis housing the 3A's separate power supply is somewhat less noteworthy, with rather ordinary C-profile metal-work acting as its top and side panels, a central green LED indicating the unit's power-on status, and a detachable IEC power cord. The power supply's inadequately damped housing appears to be at least partly responsible for some audible, yet largely unobtrusive, vibration-induced hum originating in the supply's transformer. That several Modulus owners have reported similar observations leads me to believe that a sample fault was not the cause.

Associated Components

Analogue: VPI Aries turntable, Audioquest tonearm, Benz-Micro MC Gold moving coil cartridge, Black Diamond Racing "Round Things" record clamp, Anthem Pre 1P phono stage.
Preamplifiers: Audible Illusions Modulus 3A with John Curl designed gold MC phono board, Sonic Frontiers Line 1, VTL TL 2.5, Audio Research LS15
Power Amplifiers: Celeste Moon W-5, Sonic Frontiers Power 2
Loudspeakers: ProAc Studio 150, Meadowlark Audio Shearwater
Cables: D Lin Audio Silver Bullets 4.0 interconnects, Transparent Audio MusicWave Plus , Audioquest Midnight Biwire loudspeaker cables, Cardas Hex 5C phono interconnect.
Accessories: Echo Busters room treatment products, Lead(less) Balloon turntable stand with Air Head isolation base, Target equipment stands, Black Diamond Racing Mk.III and Mk.IV Pyramid Cones, Nitty Gritty 2.5Fi Mk.II record cleaning machine, Nitty Gritty Pure-2 cleaning fluid, Stylast stylus treatment, 15A dedicated AC outlets.

The Sound
As I was between turntables for the first several weeks of the 3A's stead, its line stage was the focus of my initial attention. During that time, it became readily apparent that the Modulus' reputation for merely good line-level performance was undeserved, bettering comparably-priced units from Sonic Frontiers, Audio Research and VTL. Diana Krall's Only Trust Your Heart (Justin' Time JTR8451-2), a recording which had failed to maintain my interest when interpreted by the Sonic Frontiers Line 1, proved riveting when heard via the 3A. Ms. Krall's vocal mannerisms, which previously seemed rather trite, now somehow appealed to my musical sensibilities. Furthermore, the superior resolution and transparency of the 3A illuminated the delicate interplay between Krall, bassist Christian McBride and drummer Lewis Nash to a degree I had not heard previously.

Although I had praised the Sonic Frontiers Line 1 for its low noise floor, the Modulus 3A's all-tube line stage managed an even more impressive disappearing act. Through the 3A, music emerged from a background devoid of the low, but perceptible, level of hash and hiss so readily apparent with many competing tubed products, providing the listener with a clearer window through which the low-level subtleties of a performance could be viewed (this, after a noisy manufacturer-supplied "AA" grade tube in the line-stage's right channel was replaced with one of superior performance).

My auditioning of the Modulus 3A unearthed little evidence of the overly dark character for which the Modulus 3 had been criticized, although it did uncover the 3A's tendency to lean ever so slightly towards the warm side of neutral - a minor coloration, perhaps, but one which seemed consonant with my live music experiences. The 3A's sense of warmth and harmonic richness proved a welcome contrast to the Sonic Frontiers Line 1 (and, to a similar degree, the Audio Research LS-15) whose cool, somewhat grayer presentation lent it a comparatively thin, synthetic texture. Through the 3A, cellos, double basses and acoustic guitars weren't just vibrating metal, gut or nylon, but resonating wooden cavities, too, each with their own unique and recognizable timbre. In similar fashion, the 3A delivered vocalists complete with chests, diaphragms and nasal cavities, restoring flesh to bone and body to voice.

Without resorting to an insomnia-curing analysis of the 3A's performance across the frequency scale, I'll summarize by stating that its top end was well extended and highly detailed, its mid-band was purely seductive, if ever so slightly rich, and its bottom was tuneful and expressive, yet potent when called for. Of particular note was the 3A's depiction of the mid-bass which was unquestionably of reference quality. Partnered with the Celeste Moon W-5 (a superb solid-state stable-mate for the Modulus), and fed the appropriate source material, the 3A could astonish with its mid-bass impact and solidity. On the title track from Doug Macleod's Come To Find (Audioquest AQ-LP-1027), the 3A most certainly put the "kick" in kick drum, conveying not only the initial impact of hammer on skin, but the ambient decay which followed. In contrast, VTL's all-tube TL 2.5 line stage sounded somewhat bloated and ill-defined through the mid-bass, lacking the Modulus' tautness and definition.

In terms of soundstage transparency, the 3A was hard to fault, bettering both the Sonic Frontiers Line 1 and VTL TL 2.5. The rear of the soundstage, so often obscured by lesser preamplifiers, was brought into sharp focus by the Modulus, the listener always able to see the forest at the rear of the stage for the trees up front. During the cacophonous first-movement outbursts of Shostakovich's First Symphony (Bernstein/NYPO, Sony SMK 47614), brass and percussion tried defiantly, yet never managed to overshadow woodwinds, strings or the strangely present, yet brilliantly scored, piano occupying stage left-rear. Throughout the balance of the work, the 3A proved equally masterful at unraveling the glories of DSCH's youthful, yet remarkably mature, orchestration.

The arrival of the VPI Aries and the low-output Benz-Micro MC Gold moving-coil cartridge, had me turning my attention to the 3A's hybrid moving-coil phono stage. After a lengthy break-in period (during which time the sound of even the finest LPs was reminiscent of the early days of digital), the Curl-designed device proved to be one of superior resolution, dynamics and signal-to-noise ratio. While Audible Illusions' decision to incorporate a hybrid moving-coil phono stage in the Modulus might raise the hackles of the tube purist, doing so has resulted in a device with an imperceptibly low noise floor. Indeed, even at high volume, the only "hiss" emerging from the 3A's phono stage was that which originated on the analogue master tape itself.

Perhaps owing to its extremely high gain, the 3A's low-output moving-coil phono stage possessed dynamics of a superior sort, both on a micro and macro scale. Dynamic contrasts on the finest of analogue LPs (a list of which must surely include the brilliant Decca reissues, as well as many members of the Classic Records and Analogue Productions catalogue) oft-times startled in their uncanny imitation of life. The 3A's faithful depiction of the abrupt pianissimo-to-fortissimo progressions in the superb Classic Records reissue of Shostakovich's Symphony No. 1 (Classic Records/RCA LSC 2322) belied the theoretical inferiority of analogue's dynamic range. Will we ever see the day when a digital standard (whether it be one of a 24/96 variety or otherwise) proves to be analogue's superior in terms of dynamic contrast or that elusive quality we refer to as presence?

The tonal balance of the 3A's phono stage effectively mirrored that of its line stage; that is to say, essentially neutral, with neither the extremes of top or bottom getting short shrift. As with its line-level section, the 3A's phono stage brought the sound of the human voice to life like few others, directing my musical attention to such previously unexplored masterpieces as the Orchestral lieder of Gustav Mahler and Richard Strauss.

Comparing the 3A's phono performance to that of the standalone all-tube Anthem Pre 1P phono stage (US$ 850) left no doubt as to the Modulus' superior dynamics or its more complete rendering of harmonics. The Pre 1P fell well short of the 3A's superb dynamic and transient abilities, comparatively robbing some musical selections of life and emotion. For example, when heard via the Pre 1P, the exquisitely captured drum kit on All Roads To The River, from Janis Ian's Breaking Silence (Analogue Productions APP 027), lacked much of the impact and raw energy so readily elicited by the Modulus 3A. While certainly a fine performer in terms of mid-band purity, low-end definition and overall transparency, the Pre 1P echoed the somewhat lean voice of its more expensive Canadian siblings, failing to equal neither the 3A's high degree of harmonic and tonal splendor, nor its high-frequency air and sparkle. In a world in which four-figured phono cartridges, tonearms and external phono stages are the norm, the 3A's superbly-engineered integral moving-coil phono stage should be considered nothing less than an outright bargain.

The stock Modulus 3A is clearly a formidable performer, one that almost begs for the last ounce of sonic magic to be wrung from it. Surely one can experiment with the likes of New Old Stock tubes which carry high price tags and the promise of spotty quality, but the manufacturer-supplied (and graded) Sovtek 6922s are inexpensive, highly reliable (except for the one exception noted above) and perform well. A commonly espoused tweak is the placement of Black Diamond Racing cones between the 3A's chassis and its support, in an attempt to damp sonically-detrimental resonances in both surfaces. Indeed, utilizing three Mk. IV cones, tip down, in place of the 3A's stock feet improved clarity and transparency (most notably in the midrange), exorcised an ever-so-subtle spittiness in the treble I hadn't been particularly aware of before, improved transient speed and impact, and tightened up the bottom octaves. More than a tweak, this application of the Mk. IV cones should be considered an essential modification to the stock 3A - an inexpensive one at that.

Summing Up
Uniquely conceived and unconventionally executed, the Modulus 3A reflects one man's vision of how art should imitate life, a feat the 3A manages like few others. With affordable full-function preamplifiers becoming about as rare as a '57 Rothschild, Audible Illusions should be applauded for continuing to develop and market the Modulus 3A, a superbly musical, and highly affordable, device capable of extracting the best from both analogue and digital sources.

Modulus 3A Preamplifier
Manufactured by Audible Illusions
7066 Commerce Circle, Pleasanton CA, 94588
phone: (510) 463-9191, fax: (510) 463-8482
web:, e-mail:
Price: US$2295 with moving-magnet phono stage. Low-output moving-coil stage adds US$500
Source of review sample: Reviewer purchase
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