INTERNATIONAL AUDIO REVIEW - (46-47)
CLASS 1A

The Modulus is one of the best bargains in audio preamps today. The newest version, the 2B, is more. It is a world-class high end preamplifier at a budget price. It is the least expensive preamp you and your music can be happy with for the rest of your life!

The Modulus 2B stands head and shoulders above all the other top budget preamps in our survey here, in virtually all sonic aspects. But it does more. This $750 preamp also clobbers every other preamp under $1695, and even many priced above that (for example, it embarrasses certain tube preamps at around $3000 and $3500, and certain solid-state esoterics selling for up to $5750 and $7500).

Sonic Virtues
What does the Modulus 2B do that makes it such a sonic winner? First is its sheer musicality. It exemplifies how a preamp can converge on the accuracy of hybrid sound from the tube side (following in the footsteps of what ARC achieved with its high end tube preamps). The Modulus 2B is the paradigm of tube sound virtues at their best, with effortless open bloom and liquidity that reveals the natural texture and timbre of instruments and voices. Music sounds open, dynamic, and relaxed — not sterile and constipated like many solid state preamps. Yet the Modulus 2B is also accurate, being very transparent and clean, like the best high end preamps using solid state devices. And the Modulus has virtually none of the traditional "tube sound" vices: euphonic but inaccurate syrupy over-glamorizing of music; softening, defocussing, and/or grundging of upper frequencies; some veiling or articulation loss; high noise and/or limited gain etc. In sum, the 2B is that rarest of creatures: an audio component that combines superb musicality with superb accuracy and definition.

Musicality is a parameter that’s somewhat subjective and hard to define. But we can also talk of the M2B’s superb sonics in terms of objective parameters. Consider transparency and stereo imaging. Two things that discerning audiophiles prize most, in their music and the equipment to play this music. Two sonic achievements that are the most elusive for audio components. Two sophisticated areas in which the most exotic and expensive high end gear vies with another for top honors.

And along comes the reborn 2B version of the Modulus preamp, costing a paltry $750 with all its latest updates of premium parts inside. In virtually all aspects of stereo imaging (e.g. width, depth, localization, precision, center stage coherence, ambience, 3D space and air, etc.), the latest M2B is in the same league as the very finest, most expensive preamps available. In articulate transparency it is nearly as superb, giving way only to esoterics such as the new Rowland Research and the ARC SP11 and SP9. And the Latest Modulus 2B is no slouch when it comes to that third sonic desideratum of esoteric equipment, clean purity (lack of distortion). It’s a cause for banner headlines and rave reviews when these rare and difficult sonic achievements can be brought together in one product at any price. What’s really surprising is that you can buy such excellent performance for so little money.

But maybe it’s not so surprising. The M2B is a thorough reworking of the original Modulus which was good but not amazing. The 2A was a major update of the 2, announced at the January 1986 CES, reported on in Hotline 41, and since then reviewed favorably in some other magazines. Now there’s the 2B, with its world premiere review from IAR (plus an update here on the newly improved version of the 2B).

The 2A was already excellent; the 2B is superb. The 2A edged out all the budget competition overall: the 2B utterly clobbers them in virtually every sonic aspect, and goes on to surpass far more expensive competition, as noted above. The 2B is cleaner, more transparent, and seemingly quieter than the 2A. Resolution, imaging and a background of intertransient silence have reached a new level of excellence.

A whole new roster of premium parts have gone into the 2B: new pots, jacks, new wiring, circuit board, new electrolytic-film capacitors and a new power transformer. And there have been improvements in the power supply design. The quality and quantity of the premium parts in the new M2B would make any $1500 preamp green with envy. Yet the Modulus has gone up only $75, to $750 for the 2B version, keeping the Modulus one of the best parts bargains in all of audio. Owners of the Modulus 2A will be happy to know that they already have an excellent sounding preamp. If they wish to update, converting a 2A to a 2B will cost about $150 — which has to cover all the labor of disassembling and reassembling, as well as the total cost of all those new premium parts (not just their incremental cost over the old parts).

Some people scoff at constant marketing tweaking and incessant updates. But these are what has made the Modulus 2B a superb product and such an incredible bargain. The perfectionistic passion of Art Ferris doesn’t recognize that the Modulus is merely a budget preamp, and therefore the product design could be left to stagnate as is, with sonic performance plenty good enough for a budget system. No, the Modulus has to be brought as close to absolute perfection as possible, while still keeping its price at a budget level. To this end, Ferris evaluates the Modulus in a perfectionist audio system, where every flaw is unmasked, and every step of progress toward sonic perfection is revealed. And then every tweak that’s recently come to mind is tried: a new type of capacitor, a new value of resistor, a slight mod to the circuit configuration. The best sounding parts that can possible be afforded in a $750 preamplifier.

Throughout this continuing effort, Ferris’ primary sonic goals have been stereo imaging and transparency—as good as the very best preamps available, or as close as he can possibly get with the Modulus’ basic circuit, for the price. So it’s no accident that this heroic effort has paid off most handsomely in these two difficult sonic aspects, and that the Modulus 2B’s outstanding strengths compared to other preamps are stereo imaging and transparency (with clean purity close behind). As we discuss the Modulus’ circuit features and design considerations, we’ll see that certain aspects were dictated by Ferris’ uncompromising dedication to giving you the best possible transparency and stereo imaging.

Purist Simplicity
The Modulus is a basic preamp, with no front panel control frills, no superfluous circuitry. In the original Modulus this basic no-frills approach may have been merely a budgetary tactic. But in Ferris’ hands the Modulus 2A and 2B have turned such simplicities into the virtues of the perfectionist-purist approach, following in the tradition of the Levinson JC2. For example, there are no complex tape dubbing switches. Hence there are fewer switch contacts in the signal path to degrade the music (ref: our original SP-11 review).

Cathode follower stages that are usual in tube preamps at the outputs of the phono and line sections are deleted in the Modulus. Fewer stages mean better transparency. Low output impedance, as normally provided by the usual cathode follower, is not really necessary for the phono front end, since the leads to the first line section stage are short (this assumes that the tape out leads to your tape recorder will be kept short: and that the feedback RIAA network has a relatively high impedance and so is easy to drive). The line section uses two triodes in parallel, in effect creating an extraordinary double triode super tube, to provide a lower output source impedance (and better current drive capability). Indeed, the line section consists solely and entirely of this super tube stage. Note that this means the line section is polarity inverting, so the whole Modulus should be treated as such for all inputs.

Then there’s the Modulus’ balance control bypass arrangement. In most preamps, the signal goes through at least two pots (volume and balance) — two sets of suboptimal resistance tracks and wiper contacts to contaminate the music. Note in our PS 4.5 review, how much more transparent and dynamic that preamp sounds when its balance control is switched out of the circuit and see again our comments on the SP-10 and SP-11 bypass switch that also bypasses the balance control. Of course, these preamps must include in the signal path that switch contact which is used to bypass the volume control. But the purist Modulus, in order to optimize its transparency, bypasses the balance control for you and doesn’t even introduce an extra switch contact to do it. How? In short, there is no balance control. The Modulus simply uses separate volume pots, one for each channel. So there’s just one, and only one, pot in the signal path, with no extra switch contacts — a true purist approach.

Many customers, when asked, say they don’t like such dual mono pots, since they have to turn two knobs instead of one to change volume level, and must then readjust them for proper channel balance. But we got accustomed to the dual volume knob technique quickly, as a simple change of habit. It’s a small price to pay for the superior transparency and stereo imaging you get from the Modulus because of this control setup.

Another interesting factor enters the picture here. When you have a system that images very well (a system only made possible by superior imaging components such as the Modulus with its single pot purism), you need to micro-adjust the innerchannel balance within millibels in order to capture the best depth and hall ambience. Most stereo volume pots do not track this accurately. So, on conventional preamps, you should re-tweak the balance control every time you change the volume control; otherwise you’ll lose some stereo imaging quality. But that means turning and micro-adjusting two knobs anyway. So you might as well have those two knobs be dual mono volume pots and derive the added benefits of better transparency and imaging.

There are even plans afoot for yet further sonic improvements to the 2B, involving more new premium parts, such as expensive stepped attenuators for the volume controls and an expensive HEXFET power supply, which might be placed outboard for yet lower noise. Note that future preamps with stepped attenuators will be giving up their micro-adjustability of balance in a tradeoff to give you even better transparency. These further upgrades should be available in 1987 and will probably bring the 2B’s cost up to a staggering $795 (what’s the least expensive other preamp you know that uses stepped attenuators with discrete metal film resistors for perfectionist sound?).

Package Quality
The theme of the Modulus’ circuit, and that circuit's execution in parts, is elegant simplicity in the service of purist sound. And then that simplicity is realized with some of the best quality parts available. This same theme is then carried over to the packaging and exterior of the Modulus. Its quality package and elegant appearance would be proudly sported by a preamp costing $1500, and are quite unexpected in a budget preamp at $750. In our survey, only the two Counterpoints and the Nuance preamp came close to the Modulus in quality of construction and appearance.

Ordinarily, we wouldn’t spend editorial space and time reporting details of appearance and package construction. But here we have a budget product whose superb sonics allow it to be used in high end systems. Could this budget products’ construction quality and package appearance also be worthy of inclusion in a high end system? In the case of the Modulus, the answer is a resounding yes. Consider the chassis. A box shield is provided for the transformer. The chassis is made of more expensive aluminum rather than the cheaper steel, to avoid any degradation of the music signal by nearby steel, with its permeability and hysteresis. The top and bottom plates are attached via machined screws going through pre-tapped threads, rather than via the cheaper self-tapping metal screws going into simple holes. Even the line cord is beefy, not skinny as in most other budget preamps.

Consider the front panel area. Its elegant simplicity is dominated by two large knobs (for the two volume controls), which are expensive hunks of machined metal. This round visual theme, reminiscent of the Porsche design school looks, is then echoed in the holes milled into the thick aluminum faceplate. The rack mount holes are not round, but elongated ovals. Likewise with the holes for the pushbutton switches. The usual practice is to make these holes rectangular (for rectangular pushbuttons), and just enough for the buttons. But the Modulus places its rectangular pushbuttons within common elongated ovals, long slots with fully rounded corners. It’s a simple design touch, but it’s crucial to keeping the front panel looking uncluttered and elegant. And even now, the front panel appearance is being further refined toward a perfectionist look.

Specific Sonic Aspects & Measurements
The Modulus 2B’s tonal balance is very neutral throughout most of the spectrum, unlike most tube preamps, which have a mellow, indeed dark and murky tonal balance. This neutral tonal balance allows the Modulus’ superb transparency to shine forth to best advantage, without the adulteration of colorations one associates with traditional tube sound. This further helps the Modulus to live up to its quality of offering nearly ideal hybrid sound, combining the best of tube and solid state virtues. Indeed, one is reminded of the SP-10, which we also praised as sounding like neither tube or solid state, but instead like accurate music. This tonal balance neutrality is confirmed by our RIAA lab measurements, which shows only 12 mb too much energy in the midrange region (this is down near the 10 mb threshold of audibility).

There are three sonic aspects in which the Modulus settles on the tube sound side of the hybrid ideal. First, a relaxed liquidity throughout the spectrum reminds you that you are listening to the glories of tubes reproducing music. We find this tube type of relaxed liquidity to be far more musically natural than the artificial hardness of an equal slight error on the solid state side of the hybrid ideal would be (cf. the SA-3.1's slight hardness in the upper midrange and lower treble). Tube sound lovers should be delighted with this, since they won’t be giving up their beloved relaxed liquidity with the Modulus, yet they will be gaining all the extra transparency and articulation that this nearly ideal hybrid sound of the Modulus has to offer. In our opinion, this slight tubelike liquidity of the Modulus is just right. It is certainly not the heavy dose of syrup and defocussed softening one hears in other tube preamps such as most C-Js (which beguiles some listeners at first hearing with its sweet comfort, but soon becomes tiresome, with the sameness of the sweet flavor it imparts to all instrumental textures, and with the dark, soft murkiness with which it coats and obscures so much musical information).

Second, the Modulus 2B is very clean compared to other tube preamps, but we can still hear a trace of soft grundge compared to the very best solid state preamps (clean purity being a typical strength of the best solid state designs). This slight grundge is probably attributable to an intentional tradeoff in the Modulus design. In order to obtain more transparent, open, relaxed sound (one of the Modulus’ key strengths), extra stages such as cathode followers were discarded, and the line section super tube operates without any loop feedback. The discarding of extra stages makes the remaining tubes work harder, and also without benefit of distortion reducing loop feedback in the case of the line section. These factors naturally cause some nonlinearities. Indeed it’s surprising that the Modulus sounds as clean as it does, cleaner in fact than other tube preamps that do use these extra stages and loop feedback. We’re not bothered by the slight grundge of the Modulus, and only notice it when directly comparing it to a super clean preamp (e.g. the SP-11 and SP9). We certainly wouldn’t want the Modulus to give up any of its superb transparency and relaxed openness in trying to become even cleaner, since these are the qualities that make the Modulus great and put it head and shoulders above other budget preamps today.

Third, the sound of the Modulus in the bass regions is definitely in the tube sound camp. This is not surprising, since the Modulus is a tube preamp. It’s worth noting mostly because the Modulus is so superb at approaching the ideal of hybrid sound in most other sonic aspects. If bass quality is especially important to you, then you might want to consider one of the preamps below that approach the hybrid ideal from the solid state side (of course then you will probably have to put up with more solid state qualities in other regions too, such as upper frequency hardness). The Modulus’ bass characteristics are as good as other very good tube preamps, so there’s really no reason to squawk. It also turns out there are some very good reasons for the Modulus still having tube sound in the bass regions, and not attaining the hybrid ideal there.

First, our lab measurements show a noticeable 160 mb error in the 50 hz RIAA hinge point, resulting in too much upper bass, which sonically bestows too much richness to a plucked bass, a piano’s bottom register, etc. The manufacturer says he has done this intentionally, as an intelligent compromise to secure the best overall sound from the Modulus. You see, the reason there is too much upper bass is that the RIAA curve runs out of feedback margin at these low frequencies. This could be cured by using more overall loop feedback for the phono front end. But that would mean more feedback in the midranges and trebles, where the ear is very sensitive to the quality of reproduced music. The manufacturer says that he tried using more feedback in the front end, and it made the midranges and trebles too sterile, losing that marvelous open, relaxed quality that is the unique aspect of the Modulus’ superb transparency, and its chief ace in the hole compared to high end solid state preamps that might be just as transparent but not as musical. The Modulus used no loop feedback at all in the line section, to preserve that same unique quality. Better that this unique quality be maintained in the phone front end, even if it means a little too much upper bass because there’s not enough feedback at low frequencies.

Second. The Modulus, like all tube preamps, has a number of bass poles in series. This usually produces a weak lower bass and a loose, heavy overhang in the upper bass, in other words the characteristic tube sound bass. Technically, the poles in series produce too quick an initial decline in the bass step response (giving too little kick in the low bass), with subsequent overshoot (which creates the ill defined overhang in the wrong polarity). For further discussion and examples, see IAR Journal 3 and Hotline 42. Any tube preamp could have outstanding bass, but it would involve wide staggering of capacitor values, and thus great expense for some large value capacitors (30 mfd or more worth of caps in parallel at some point in the circuit). Obviously this is not feasible for any manufacturer to put into a budget preamp. Of course, by adding aftermarket capacitors, a hobbyist can vastly improve the bass of the Modulus (or any other preamp with bass problems, including some solid state as well as all tube units). Our lab measurements show that the Modulus’ bass quality is indeed typical of good tube preamps; there’s a 22% overshoot and a 45 ms time constant (through the phono input).

The treble tonal balance of the whole Modulus (through the phono input) changes slightly with the volume control setting. It’s not a serious problem, but it is noticeable to the alert listener or the competent reviewer. The following paragraphs will explain this phenomenon.

Below the 12 o’clock setting of the volume control, the trebles are too bright, and stick out a bit inconsistently above the midranges. The trebles also have a little too much bite, making this part of the spectrum a bit more solid state than the rest of the music through the Modulus. Additionally, this bite was a little too hard in quality (giving a hint of solid state artificiality) until a recent improvement to the 2B, which substituted a HEXFET for the former bipolar device in the solid state power supply regulation, smoothed down this slight hardness.

Then, around the 1 o’clock setting of the volume control, all these minor problems disappear. The Modulus is utterly magnificent. The trebles sound flat, the tonal balance is neutral and consistent with the rest of the spectrum, transients have just the right amount of hardness, and there’s no hint of excess or artificial bite.

Then, between 1 o’clock and 4 o'clock, the trebles become too rounded in quality and slightly dull in quantity. The Modulus trebles sound more traditionally tubelike. And there’s the psychoacoustic illusion of less transparent articulation and individualization than the Modulus is really capable, because the attack part of individual musical transients and details has been slightly muted.

At the 4 o’clock setting of the volume control, things become quite neutral again, though not quite as perfect at 1 o’clock. And then above 4 o’clock the trebles become too bright again, as they were below 1 o’clock.

Our lab measurements corroborate these sonic effects we hear, and suggest the reasons why they occur. Below 1 o’clock on the volume control, the RIAA square wave response shows a very high needle spike, which reaches 33% at the worst case setting (about 10 o’clock). This is probably due to a common (but easily correctable) phenomenon in many preamps’ feedback RIAA front ends; a zero at a very high frequency that causes a leveling out of the RIAA de-emphasis, hence a rising supersonic response (see IAR Journal 3 for discussion). If the zero is at a very, very high frequency, the resulting spike will be very thin, and there will be negligible brightening effects within the audio band (though there might well still be added distortion problems from the overemphasized ultrasonics and difference frequency byproducts). But the Modulus’ spike has enough thickness (5 microseconds) to cause audible time domain hardening of transient attacks (the leading corner has an extra spike of energy). This thickness also indicates that the zero is at a low enough frequency to cause a rising frequency domain response within the audio band and audible brightening of the trebles (we measure the rise beginning at 12 KC, and reaching +1.3db at 30 kc, when the volume control is in the 10 o’clock worst case position).

Why does this measured spike (and the treble sound) of the Modulus change with the volume control setting? What’s probably happening is that the source resistance of the volume control (which normally varies dramatically with its setting) acts in concert with the input Miller capacitance of the line section parallel super tube, to form a varying high frequency RC filter. As you raise the level of the volume control, its source impedance gets higher, making this RC high frequency filter cut in at a progressively lower frequency. The worst case for this (logarithmic) control’s source resistance is up around the 2:30 o’clock setting (above which it declines again). At the 1 o’clock setting that sounds so marvelous, the roll-off hinge frequency of this high frequency filter pole evidently perfectly matches the hinge frequency of the zero that causes the rising response and the time domain spike. These rolloff and rise hinge frequencies are supersonic, just beyond the audio band, but the skirts of these filters have effects down into the audible treble regions. Since the zero causing the rise and the pole causing the rolloff are both single (real) pole RC phenomena, they can perfectly offset each other, with their skirts in the audio band perfectly canceling each other out to give virtually the perfect time domain and frequency domain response.

Sure enough, our lab measurements that at the 1 o'clock volume control setting the Modulus has incredibly perfect square wave response. This precisely corroborates our sonic finding that the Modulus sounded best and most neutral at this volume control setting. There's no trace of the spike at the leading comer of the square wave, which gave a slightly hard quality to trebles. And there's no rounding of the leading comer, a usual symptom of tube preamps and limited bandwidth solid state designs, which gives music's trebles a rounded and even soft quality. Instead, there's the textbook perfection of a square corner. So here's scientific evidence of how well the Modulus approaches the hybrid ideal, especially at this volume control setting. The Modulus still has the slight liquidity and open, relaxed quality that epitomizes the best characteristics of tube sound. But it also has superb articulation and accurate transient hardness, like the best characteristics of solid state sound, as evidenced by that perfect square wave comer without rounding.

At volume control settings between 1 o'clock and 4 o'clock, the frequency of the RC rolloff pole goes lower, below that of the zero rise, so its effect predominates. The square wave response has a rounded leading comer, with about a 7 microsecond risetime at the worst case setting of about 2:30 o'clock. This is why the Modulus' trebles sound rounded and tubelike with the volume control set in this region, and why the trebles seem to have less transparent articulation and accurate bite than the preamp does at lower volume control settings.

Above 2:30 or so, the source impedance of the volume control starts dropping, and by 4 o'clock the frequency of this RC rolloff is once again matched to the frequency of the rise from the feedback zero. But this time some other secondary effects must be entering the picture, for the square wave response is not quite so perfect as it was at 1 o'clock, with a slight leading comer spike followed by a little valley dip.

Then beyond 4 o'clock, as the source impedance of the volume control keeps falling and the frequency of its RC rolloff keeps rising, the leading comer spike from the feedback zero once again predominates.

Most preamps sound better at some volume control settings than others. Recall for example that the SP-11 sounds best with its gain control kept at maximum. So it is no great sin that the Modulus sounds different (and can be measured to perform differently) at various volume control settings. Rather, this is a phenomenon that is interesting for discussion, especially if you want to hear the Modulus performing at its best. If the Modulus were a merely good preamp instead of superb, it wouldn't matter that much where one set the volume control, if indeed one could even hear any differences (notice that no other preamps in this survey merit such a discussion). But preamps like the SP-11 and the Modulus 2B are so transparent and articulate that you can easily hear the optimization points for everything in your chain, including the control settings of the preamps themselves. The Modulus most nearly approaches the musical accuracy of the hybrid sound ideal at the 1 o'clock setting of its volume control, and that's one guideline to keep in mind for getting the best from this remarkable budget preamp (other guidelines follow below). It's also important for you to be aware that you can expect the Modulus to have slightly too much treble brightness and slightly too hard a treble bite below 1 o'clock, and conversely to have slightly too rounded and dull treble transients between 1 o'clock and 4 o'clock. You might prefer one sonic personality or the other, and that's fine for your taste. But beware of what others tell you. If someone tells you that the Modulus sounds very good except for a zippy high end, ask him where he had the volume control set. Conversely, be suspicious if someone tells you that the Modulus sounds very good except that some vital aspects of music are smoothed over and softened, such as sharp transient edges, attack of hard notes, or naturally piercing sounds; chances are he had the volume control set between 1 o'clock and 4 o'clock, and so never even heard the magic of the Modulus' true transparent articulation capabilities.

How to Get the Best From Your Modulus
The Modulus 2B can hold its head high even if mated with the finest, most expensive audio components in the rest of the playback chain. It certainly deserves associated components as transparent and articulate as your budget can manage. So this is our first guideline for you. It would be a big mistake to have some link in the chain of the dark, murky, blurring, and mushy school. Just one such weak link in the chain can totally mask the articulate transparency of the rest of your chain, including the Modulus as a preamp. It would be a fatal mistake for you (or a reviewer) to evaluate the Modulus with such a link in the chain, since you could never hear the Modulus' greatest sonic strengths in their true measure. For example, if you have a traditional MM cartridge with the usual mushy, grungy sound, you should upgrade to a recommended high resolution, high output cartridge (e.g. the Monster Alpha 2 HO, Nagaoka MP-50 Super, or Grado MCX — the latter two listing for $250 and $300, and possibly available at discount, since all cartridges have a high markup). Likewise, a power amp with old fashioned tube sound would be inappropriate, since it would hide the Modulus' best sonic abilities, especially in its nearly ideal approaches to hybrid sound. A neutral, transparent, and articulate budget power amp such as the Counterpoint SA-12 (or perhaps Audible Illusions' own forthcoming power amp) would be a far better choice than a Conrad-Johnson or NYAL Moscode.

Conversely, you should take care that no link in the chain is excessively hard or zippy bright. The accurate neutrality of the Modulus will not hide this as well as the more obscuring preamp you may now be using. If you audition the Modulus in place of a mushy preamp and think the Modulus sounds artificially hard, take care that the cartridge and speaker system's tweeter do not have artificial peaks that you're hearing accurately revealed for the first time.

Our second guideline for you concerns absolute phase polarity. The Modulus instruction manual alerts you that the Modulus inverts absolute phase polarity (in its line section), and gives detailed instructions for connecting your system properly to accommodate this. It's no sin for a product to invert polarity, provided the manufacturer tells you, so you can hook up your system correctly (see IAR Journal 4 for discussion of the whole phase polarity issue). Indeed, the Modulus surely sounds more transparent by virtue of deleting the extra tube stage that would be required to convert the phase polarity back to non-inverting.

It's crucial that you follow the Modulus’ instruction book, and connect your system in the proper absolute polarity for the Modulus, as well as your cartridge, some of which are also inverting (see IAR Journal 5), and your head amp if any (see Hotlines 1 & 2). If you fail to do this, you won’t hear much of the articulate transparency at which the Modulus is so superb. That's because listening in the wrong absolute polarity, especially through a high resolution device like the Modulus, makes music sound very different. The wrong polarity creates a dramatic softening in quality and a moderate depression in quantity, especially in the midrange, upper midrange, and lower treble. This softening makes subtle details, including timbre and texture, seem hidden, smoothed over, or blurred together, as the waveform transients which define them will be pointing in literally the wrong direction. The natural bite of instrumental attacks and transient edges will be severely diminished. Moreover, the tonal balance depression from listening in the wrong polarity, centering in the upper midrange, would also diminish much of the musical information, centered in this same region, which tells you about instrumental textures, transients, and 3D hall space and ambience. Two broad classes of musical instruments are affected worst by listening in the wrong polarity: instruments that are blown (woodwinds, brass, human voice) and instruments that are struck or plucked (drums, piano, harpsichord, plucked strings). But the effects are also dramatic on some others, such as legato strings, where the textural sounds of rosin and wood depend upon subtle details in the upper midrange.

Our third guideline concerns using a cartridge with high enough output, lest the superb transparent articulation of the Modulus be masked by noise. The noise level of the Modulus is low compared to other tube preamps, but still falls within the medium category overall when all preamps are compared on the scale, including solid state ones with their typically low to very low noise. This means that low to moderate output MC cartridges are not ideal for the Modulus. It is, after all, basically an MM input phono preamp, designed for high output cartridges.

The gain of the Modulus is a normal 60 db. So, if you use a cartridge with a 1 mv output, you could, by turning up the volume control all the way, just barely get the 1 volt preamp output level commonly needed to drive a power amp to its full output. And indeed, the manufacturer supplies a list of recommended cartridges that begin with a nominal 1 mv and up output level. But we think that’s a bit too inclusive, if you want to hear the Modulus at its best. We recommend a cartridge of at least 1.5 mv output, beginning with the Monster Alpha 2 HO (the Grado and Nagaoka have even more output). If you use a cartridge with less output level than the Alpha 2 HO directly into the Modulus, then the background noise level will be too high.

Remember, the crucial problem with too high a background noise level is not simply the background noise per se (which doesn't bother some listeners, just as tape hiss doesn't). As we discussed in the introduction, too much background noise will soften and veil the music, especially subtle details and especially upper frequency information. Thus, this noise will seemingly degrade the transparency and articulation of the preamp; even the dynamics might seem to suffer, because the initial transient attacks will be blurred and smoothed over. You won't be hearing the true capabilities of the preamp. But it won't be the preamp's fault, if its MM type phono front end was never really designed for the much lower noise levels needed for MC cartridges (of low to moderate output). Rather, it will be your fault, for following that naive fad of plugging all sorts of cartridges directly into a phono preamp, in the mistaken belief that fewer amplifying stages should always produce better sound. A given amplifier stage won't produce better sound if it wasn't designed to handle a signal you feed it that is too low in level (or too high in level for that matter).

Because the Modulus is so superb at transparency and articulate accuracy (and open, relaxed dynamics), it's particularly crucial that you follow this general advice of using a high output cartridge (if you're going directly in without a head amp). If you don't follow this advice, you will be literally throwing away the Modulus' chief sonic strengths, to the point where it might not sound that much better than some other competing preamps under $2000. This is relevant if you want to buy the Modulus and use it to best advantage in your system.

Moreover, it is of particular relevance if you are comparing the sound of the Modulus to another preamp. Using a cartridge with too low an output will veil and soften the sound, hiding or masking the differences between the two preamps. More importantly, this veiling and softening will adversely affect the articulate transparency of the Modulus more than it would affect the sound of the other preamp, if that other preamp were itself inherently softer and more veiled than the Modulus. Think about that. Even if the two preamps were to have an equal noise level, the softening, defocussing, and veiling imposed by high background noise would scarcely affect the other preamp if its sound were already intrinsically soft, defocussed, and veiled. But the glories of the Modulus' sound would be drastically degraded, perhaps to the point where it would not seem any better than the other preamp. If the noise level of the Modulus were slightly worse, or different in spectral balance, the truly veiled and softening preamp might even seem to come out sounding more articulate and transparent than the Modulus, if you use a cartridge directly in with too low an output level. The central point to remember is that you won't hear the true sound of any transparent, articulate, dynamic preamp (such as the Modulus) if you throw a monkey wrench into the works by using too low a signal into the preamp. Anyone comparing preamps should beware that his testing procedures are scientifically correct in this regard, lest his sonic comparisons be rendered utterly invalid.

Our fourth guideline concerns the setting of the volume control. Recall that the Modulus sounds best in the trebles, and gets closest to the ideal hybrid sound there, when the volume control is set at 1 o'clock. Above this setting, until 4 o'clock, the Modulus' trebles are somewhat rounded and dull, and transient details and attacks lose their natural bite via a slower risetime. So if you think the sound of the Modulus has these problems (or their consequences, such as seeming too smoothed over or softened), check to see if you have the volume control between 1 and 4 o'clock. If you do, you are not hearing the Modulus at its best — and any comparisons with other preamps would not be representatively fair of what the Modulus can sonically achieve. Furthermore, if you do have the volume control set way up beyond 1 o'clock for normal listening, it probably means that you are using a cartridge with too low an output level (we say probably because of different loudspeaker sensitivities, etc.), and if you are, then you are further degrading the Modulus' inherent sonic strengths of articulate transparency, as discussed in the third guideline above. In other words, you are hitting the Modulus with a crippling double whammy: too high a noise level from too small a signal, and a volume control setting between 1 and 4 o'clock. Both of these act in the same direction: softening, defocussing, dulling, smoothing down, and veiling the music — especially transient details that bestow texture and timbre, and transient attacks that bestow dynamics and proper bite. Forcing both effects upon the Modulus gives a grossly unfair portrait of its sonic capabilities, particularly of the very sonic aspects in which it most excels.

The simple solution to this unfair double whammy is to employ a cartridge with a high enough output level, or add a quality head amp.

Conversely, if you think the Modulus treble sound is too bright or has too much hard bite, check to see if the volume control is set below 1 o'clock. If it is at 1 o'clock or higher, then something else in your system is too bright and/or hard in the trebles, and perhaps the Modulus' accurate hybrid sound is revealing it, while a previous preamp with old fashioned dark tube sound had hidden it. If the Modulus volume control is below 1 o'clock, you can make the Modulus' trebles more accurate, less bright and hard, by taking steps to achieve that ideal 1 o'clock sound.

What steps can you take? Several alternatives are open to you. You could reduce the gain of your electronics, in the Modulus or in your power amp (easy if the amp has an input level control). A technician could easily wire a voltage divider fixed attenuator into the Modulus, using a pair of Resista resistors per channel, such that you wind up doing your normal listening at the 1 o'clock setting instead of (say) the 10 o'clock setting. Another tactic would be to raise the source impedance of the volume control, by putting a single resistor per channel in series with it. This would not significantly change the gain of the Modulus or your electronics. But it would lower the volume control setting at which the RC treble rolloff perfectly balances the RIAA zero treble boost. The proper value series resistor could lower that perfect balance setting from 1 o'clock to the setting where you normally do your listening.

Note that in all cases the correct resistor values are determined by variables peculiar to your system and listening habits, so there is no single magic value that we could tell you to install in this article. However, a industrious technician could work out a universal conversion table, which would essentially say: if you presently listen to the Modulus with your volume control set at X o'clock (some position below 1 o'clock), then you can install a fixed attenuator of ratio Y to take you to a 1 o'clock setting for normal listening, or you can install a series resistor of value Z ohms to bring the balance point down to your setting of X o'clock. To repeat, if on the other hand your present listening position is above 1 o'clock, then you need a higher output cartridge (unless you like the trebles mellow, just as you're hearing them between 1 and 4 o'clock).

We've discussed four important guidelines for getting the best sound from your Modulus. All four guidelines should be followed to appreciate the greatest strengths of this special preamp in their true form. Neglect any one, and the Modulus won't seem to sound as transparent and articulate as it really is.

And of course it’s possible for someone to royally screw up and do all four things wrong. He wouldn't hear even a glimmer of the Modulus' greatest strengths. Just imagine this quadruple whammy situation. First, this someone listens to the Modulus through an old fashioned tube sound power amp, which with its murky, dark, congested, and soft sound utterly masks the hybrid ideal of the Modulus' transparent articulation, making it sound no better than other old fashioned tube preamps. And second he also forgets to invert the absolute phase polarity when listening to the Modulus, thereby making it seem even softer, more smoothed over and less articulate, and darker and murkier, especially in the region centered on the upper midrange that's so critical for high definition and is so cruelly crippled by listening in the wrong phase polarity. This would also put the Modulus at a special disadvantage if it was being compared against another preamp and that someone listened to the other preamp in the correct phase polarity. And third he uses a cartridge with too low an output level, so the Modulus' articulate transparency is degraded by background noise, making it sound more like a veiled and soft old fashioned tube preamp. And fourth he has the Modulus' volume control set way up, between 1 and 4 o'clock (quite likely if he is using a cartridge with too low an output), which also makes the articulate transparency (at lower settings) more rounded, soft, and sluggish.

All four whammies would be working in the same sonic direction, smoothing over and veiling subtle detail, and softening transient attacks. Thus, if all four mistakes were made by someone, the Modulus would be unrecognizable, seeming to be a mere shadow of its true articulate and transparent self. The Modulus would seem to be to a grossly different preamp than it really is. I can just foresee these mistakes, perhaps all four of them together, being made by one of the many junior amateur reviewers contributing to the underground magazines nowadays. Obviously his review would be totally irrelevant to the sound that you and I can hear from the Modulus 2B. His review would be at odds with the rest of the world.

Incidentally, it's worth mentioning in passing that dealers who happen to carry both the Modulus and the Conrad-Johnson PV-5 (a preamp sometimes compared in reviews to the Modulus, even though it costs twice the price) report that they have trouble selling the PV-5 if they let the customer listen to both. There's also a big difference in reliability track records, with the Modulus 2 series being excellent, while C-J products are noted for suffering from assembly QC flaws. The PV-5, however euphonic its sins might seem, belongs to the old fashioned tube sound school, with dark colorations and congested murkiness. Nearly everyone who listens to both preamps prefers the modem tube sound, the greater transparency and accuracy, that they hear from the Modulus, provided of course that the Modulus is fairly set up, following the four guidelines.

Update
We released the first half of this review at January CES, but delayed printing it in IAR until we had a chance to test in our lab three very important new preamp prototypes, to see where they would fit in the scheme of our top budget preamp survey (see Class 1b below). While we were waiting, the improved version of the Modulus 2B (anticipated above) came into the lab.

The latest 2B features a HEXFET instead of a bipolar device in the power supply, Tiffany jacks, and soon the stepped attenuator (already installed in the unit we received to test). The latest 2B sounds even more transparent, more refined, and even slightly cleaner and quieter. It's more of a sonic winner than ever.

The anticipated tradeoff of the stepped attenuator has indeed come to pass. It does afford even better transparency and cleaner sound than the continuous pot. But it has discrete steps, so you cannot fully obtain the Modulus' stereo imaging capabilities, since hearing optimum ambience and depth requires precise balance adjustment (for your cartridge and then for each recording), by an amount smaller than the discrete steps built into the stepped attenuator. For some listeners the last bit of transparency is more important than the last bit of imaging ambience and depth, while for other listeners it is the other way around. We suspect that Audible Illusions might be persuaded to keep making some Modulus 2Bs with the old continuous pots for the latter group of listeners. This would be the optimum imaging Modulus, while the version with the new stepped attenuator would be the optimum transparency Modulus.

It's a tribute to the sonic prowess of the Modulus 2B that all these subtleties can be appreciated and optimized. With most lesser preamps, you wouldn't even be able to hear any differences. The Modulus 2B gives you nearly ideal hybrid sound in most aspects, and is the first and only preamp to do this so well at a budget price. It gives you the best of high end solid state sound: articulate transparency, accurate neutrality, and clean purity. And it also gives you the best of high end tube sound: naturally liquid timbres, relaxed ease, and open dynamics. Then there are virtues like superb stereo imaging, in the same league as the best of either solid state or tube preamps. And of course it's reassuring to know that the Modulus gives you such high quality parts, packaging, and construction, leading to an excellent reliability record. All this together in one product makes the Modulus 2B quite a preamp at any price, a true world class high end preamp. When you then consider that this Modulus 2B costs less than $800 — well, need we say more?