Musical Fidelity X-10D line-level preamplifier Muse Kastanovich August 1997
The conventional wisdom states that the more electronics one inserts into an analog signal path, the worse the resulting sound. This wisdom is true only to a point: Taking simplicity too far can result in a cure worse than the disease. At one extreme you have many excessively complicated circuits, far more than you'd ever really need to get the job done; by the time the music makes it through this tangle of electronics, it's been mangled. At the other extreme is a circuit so bare-bones it can't even accomplish the necessary amplification and control of volume, much less do so with low distortion. Where, between these two extremes, is that magical point of greatest performance?
Many line-level "add-ons" have been claimed to improve the sound when inserted into a stereo system, taking it closer to that point of greatest performance. Equalizers, dynamic-range compressor/expanders, the Aphex Aural Exciter, the BBE Sonic Maximizer, the Taddeo Digital Antidote, and others have attempted to improve whole systems. In a very-high-quality system, however, these add-ons are just as likely to take away sound quality as they are to restore it. In addition to what they're supposed to do to the signal, they often add measurable distortion, and other, audible distortions as well.
Enter the Musical Fidelity X-10D and the Z-Man Audio Signal Enhancer line-level analog buffer stages. Both of these were designed to be used with CD players and inexpensive D/A converters "to take out the excessive brightness and grain" inherent in the CD medium. (I certainly know all about these annoying qualities of CD; many of the discs in my collection could use some "enhancement.") These two buffers attempt to make inexpensive CD-player output stages sound better by presenting them with a high, easy-to-drive input impedance. The buffers' output impedances are low to better drive both cables and a preamplifier's input.
The $199.95 X-10D is an interesting-looking piece of equipment: The main chassis is a black cylindrical extrusion, but, thanks to two integral support rails, it won't wobble or fall down. Stuck to the bottoms of these rails are four small, rubbery feet (one of which I managed to lose during the review and the other three JA subsequently lost). These feet couldn't be very expensive, so a couple of extras should be included with every unit. Other Musical Fidelity products that also use this unusual chassis are also available. The front panel is a disk of bare, beveled aluminum 3/8" thick, with a red power indicator. On the back panel are the gold-plated, plastic-body RCA input and output jacks, and the AC power input. The power transformer is a separate 12VAC "wall wart."
The two tubes are US Philips 6DJ8s, one used for each channel, presumably as cathode followers. The inputs are coupled through 0.22µF film caps, the outputs through 2.2µF film caps. The resistors are high-quality ¼W metal-film types. The two tubes' heater filaments are fed quiet DC current, rather than AC as in the Z-Man. The main supplies have 6000µF of Jamicon electrolytic capacitors—not as much energy storage as you might think, since the supply is bipolar and the voltages are fairly low. The X-10D does continue operating for a few seconds after power is removed, always a good sign. Two TO-92 cased 3-pin devices regulate each voltage rail.
The X-10D was broken-in for more than 50 hours before I began my critical listening. The unit was left on continuously to avoid warm-up time before listening sessions. Though the X-10D increases the signal level by about 1dB, potentially skewing listening perceptions, this difference appeared to be small enough that any effect it had on perceived sound quality was completely swamped by qualitative differences inherent to the unit.
I began the listening comparisons in my main system with the excellent Rotel RDD-980/RDP-980 transport/processor, these connected by two jitter-reduction boxes in series (see Sidebar). These were fed into an Audio Electronics AE-2 preamp, Zen SE MOSFET power amps, and B&W 804 speakers. This system is a bit of a worst-case scenario for the X-10D in that it is already fairly optimized, with a well-balanced and lively presentation. And remember that all my comments refer to the effect of inserting the buffer and a pair of interconnects.
Putting on the 1993 digital remastering of Axis: Bold As Love (MCAD-10894) by the Jimi Hendrix Experience, I noticed a slight upper-bass emphasis with the X-10D. Everything was slightly veiled and softened a little. The low and midbass appeared to be rolled off, making them sound less meaty. The leading edges of transients had less impact, which made Jimi's guitar playing sound slower and lazier, and "lazy" is one way Jimi never plays. Mellow, maybe, but not lazy. Rhythm and pace seemed to be diminished.
Moving on to the Audio Alchemy DITB D/A converter, I listened to Sanderling/Ireland NSO playing Tchaikovsky's First Orchestral Suite (Naxos 8.550644). There seemed to be less detail available with the X-10D buffering the DITB than without. Harmonic colors were less realistic, the oboes sounding a bit like clarinets. There was less air in the violin tone, and everything sounded too fluffy. The instruments attacks didn't sound as fast, making the tempo seem lethargic. The low frequencies seemed more limited. Substituting the overachieving $250 NAD 510 CD player or the $349 Denon DCM-360 CD changer didn't give different results.
The Musical Fidelity X-10D was then inserted into the real-world system in my living room, where I break-in loudspeakers, in this case the Signet SL256 minimonitors I reviewed in June '97 (Vol.20 No.6). The room itself is reverberant; speaker placement is semi-nightmarish, with one cabinet perched atop the TV and one on a wooden box in the corner. The CD players drove either the buffer or an NAD 1600 tuner/preamp, this plugged into an NAD 2100X power amp. Interconnects were affordable Straight Wire Laser Links, veterans of many systems. Speaker cable was 14-gauge stranded stuff. This is the kind of system that nonaudiophiles and college students listen to every day, if they're lucky.
I enjoyed the Cranberries' To the Faithful Departed (Island 314-524 234-2) through the Denon DCM-360 in the real-world system. Overall, things sounded more timbrally correct after the insertion of the X-10D, though pace and timing were still affected. The fast drum rhythms were not as clear, nor were guitar rhythms as well pronounced. The midbass still sounded a touch rolled off (footnote 1). Dynamics were decreased, and detail was partially veiled.
The Musical Fidelity X-10D was auditioned with and without AC power conditioning, in two completely different rooms, with four different digital sources ranging in price from $250 to $2000, and with two different preamp/amp/speaker combinations. It was tried with different interconnects and speaker cables, and with many different types of music and recording qualities. In only two of these configurations did the X-10D improve the sound. However, it did seem to make electric guitar timbre truer, and could improve the sound of synthesizers (must be those vacuum tubes). Guitar pace and timing was always worsened, though.
After many listening tests, it became clear that the Z-Man preserved more of the music's dynamics and clarity than the X-10D, but only by a thin margin. I found no combination of components that sounded better overall when the X-10D was added. This is too bad—I admire its high engineering and parts quality. In this case, it seems that the conventional wisdom concerning the benefits of simpler analog circuitry is true.
To those looking for ways to improve their systems without exchanging any of their gear for new components, my advice is to try a jitter-reduction box (see system sidebar) or an AC power conditioner. These are two types of devices that, when incorporated into an appropriate sound system, and unlike the buffers reviewed here, seem to offer sound-quality benefits with no drawbacks.—Muse Kastanovich
Footnote 1: Technically speaking, the Signet SL256 has no low bass; its low-end capabilities do not extend below 40Hz.—Muse Kastanovich