Once upon a time, all audio equipment used vacuum tubes. In recent years, however, tubes have become the exclusive province of super high-end audio. It is more expensive to accomplish any particular task with tubes than with transistors, and few manufacturers (with the exception of Conrad-Johnson) seemed willing until now to refine their techniques and pare back their budgets to make tube components more affordable.
The success of expensive tube units, however, has prompted a number of manufacturers to offer “budget” tube preamplifiers. Though still not cheap, they come in at prices just a bit higher than the least expensive solid-state preamps (Hafler, Kenwood, etc.). Consequently these lower-cost tube units are enjoying more than a little success.
In this issue I’ve reviewed three of these budget tube preamps: the Conrad-Johnson PV4 ($485), the Counterpoint SA-7 ($595), and the subject of this report, the Audible Illusions Modulus ($450). The design philosophies of the three are similar in a number of ways: each uses dual triodes in varying numbers; all are products of the minimalist school, having no tone controls and only the most basic of features; all three preamps invert polarity; and all three designs produce sizeable turn-on and turn-off noises—be sure you turn your amp on last and off first.
The Modulus is a basic black and silver box, though somewhat more attractively styled than the C-J PV4—a wider, sleeker box suitable for rack-mounting. The separate volume controls for each channel at first seemed cumbersome to use, but were easy to get used to. The power supply is housed in a separate unit, the cord to which is not detachable; ie, the power supply must be carried with the unit whenever the preamp is moved. Also, the 42″ length of the cord is somewhat shorter than I would have liked.
Sound Quality
The Modulus excelled in several areas where the PV4 fell short. High frequencies were nicely extended and open, free from noticeable hiss or grain, and open sounding. The upper midrange/lower treble was slightly dry, and instruments such as cymbals sounded just a bit forward. Female voices tended to be somewhat sibilant (footnote 1).
Bass extension was exceptionally good for a low-priced tube unit. There was a slight softness in the very low bass, but level and weight were very good all the way down. The upper bass/lower midrange was slightly warm, but not noticeably accentuated.
Dynamics also were good. The Modulus did particularly well in this regard on percussion and piano, the difference between pp and ff being shown with exemplary accuracy. The Modulus did, however, occasionally sound congested during very high-level, complex orchestral passages. In these instances the soundstage would collapse, the result being a constriction of sound and a confused image.
Detail and harmonic contrasts were good, though the Modulus did not equal the PV4’s outstanding abilities in this area. In fact, I was surprised at the amount of detail presented by both the Modulus and the PV4—no mushy tube sound in either case. Image width was good and depth fair but, like the PV4, individual instruments and voices were a little too broad.
Interconnects
Since all of these preamps have higher output impedance than most solid-state preamps, cable matching becomes fairly important. The Modulus and the SA-7 underwent substantial changes as different cables were tried. Higher-capacitance cables gave the Modulus some problems. Monster Cable and Apature both worked nicely on the Modulus. Many of the other audiophile cables caused excessive brightness.
Conclusion
As similar as the Conrad-Johnson, Counterpoint, and Modulus preamps seem in price and design, they sound radically different—more so than anticipated. Except for the lack of a typical transistor sound, none of the three neatly fit the stereotyped notions many audiophiles have of tube equipment. In fact, I’ve heard several solid-state preamps that have more of the characteristics customarily ascribed to tubes than do these units.
Both the Conrad-Johnson PV4 and the Audible Illusions Modulus offer very good performance, and can be highly recommended in view of their prices. I suspect the choice between the two will depend greatly on the other equipment with which they will be used. The PV4 would seem the clear choice with speakers such as the Stax F81s or Quads, which are capable of showing the PV4’s ability to reveal detail and harmonic contrast, but not fully capable of utilizing the Modulus’s dynamics and frequency extension. The Modulus, on the other hand should mate well with speakers such as the Linn Sara or Dayton Wright LCM-l, which have good dynamics and frequency extension, but which are not capable of revealing the nth degree of detail. I tried the Modulus/DW combination, and found it to work very well.
The differences between the Modulus and PV4 also point out that though both products offer good value for money, neither approaches perfection. I came away from this review with a hunger to try their bigger brothers, the Audible Illusions Uranus and Conrad-Johnson Premier Three. Before buying one of these low-priced units, potential purchasers should be aware that for under $500, a tube or solid-state preamp must incorporate some compromises. In my opinion, however, both Conrad-Johnson and Audible Illusions have done an excellent job of compromising (footnote 2).
Footnote 1: I was more impressed with the Modulus than was SWW, possibly because my sample of it was better than his. I felt the high end was very good, and did not notice anything I would describe as a “zippy” quality. In fact, I think the Modulus is a steal at its modest price.—J. Gordon Holt
Footnote 2: Michael Fremer subsequently reviewed the Audible Illusions Modulus 3A preamplifier in February 1996.—John Atkinson
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COMPANY INFO
Audible Illusions
PO Box 2537
Daytona Beach, FL 32115
(386) 676-2004
www.audibleillusions.com
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Specifications
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