The Mod Squad Line Drive passive preamplifier

The Mod Squad Line Drive System Control Center is a purely passive stereo switching unit with a volume and balance control, five line inputs, and additional facilities for two tape decks. It allows the audiophile to replace a preamp, with its active gain stages—and resulting coloration—with a device that introduces no distortion or coloration other than that in the wiring, switches, and controls.

Construction is also of very high quality, even for a $400 device. Tiffany jacks are used selectively for two pairs of inputs and one pair of output jacks. The unit uses Lorlin selector switches. Wonder Wire, Wonder Solder, and Teflon-insulated LC/OFC wiring. Construction is on the battleship side, and the styling and feel are excellent (footnote 1).

Having said this, I have to confess that I have mixed feelings about the Line Drive. I do have to say that it performed very well with a wide range of electronics. In fact, it provided cleaner sound on high level stages with all electronics with a reasonable gain and impedance match than any active preamplifiers I could try, with the exception of the Audio Research SP-11 and Krell KRS-2.

Like the PS Audio 4.5 and 5.0 when used in their purely passive modes, the Mod Squad Line Drive demonstrates all too clearly that many preamplifier designers have spent too much time on their phono stages and too little in making sure that their line stages are totally neutral. The vast majority of high-end preamps simply cannot meet the challenge of the equivalent of a straight wire bypass with controls. As a result, it is clear that you can get a unit for $400 that will outperform most active preamps, including some costing six times as much.

Further, the Line Drive is, in my opinion, infinitely preferable to the use of a CD player directly into an amplifier simply because it provides a higher-quality volume control and a balance control. No serious audiophile is going to be so much of a purist as to eliminate the balance control, simply because so many recordings have slightly unbalanced channels. Since the balance control acts as the "imaging control," and minor adjustments are essential to getting the proper spread and depth of instruments from right to left, no halfway decent system can do without one. Only an audiophile content with a system that never had proper musical focus could bear to listen to music without at least occasionally adjusting system balance.

If this makes the Mod Squad Line Drive sound like an incredible bargain, let me mention two major reservations. First, as a lukewarm member of the "analog record must never die" club, I should stress that the Line Drive is based on the thesis that the sound of compact disc has advanced to the point where the audiophile can now eliminate the phono gain stage in a preamplifier, and rely solely on the high-level gain stages of his or her CD player, tuner, tape unit, or DAT. While I realize that some separate phono preamps are still available, I know of none that I would want to use in a purist system, and while the Mod Squad is developing one, I have not heard it and cannot comment on the resulting cost-effectiveness of mixing it with the Line Drive (footnote 2).

I'm not sure that I'm ready to advise anyone to take the risk of not buying a unit with a top-quality phono stage, no matter how well CD or DAT perform. I still prefer analog phono for reference listening, and I've heard more CD players and digital tape units than most. More importantly, I would be worried about giving up so much music that is only available on record. The point of audio gear is not, after all, technical excellence, but access to music.

Second, I have some question about how well a purely passive control unit can deal with the problems of impedance matching, buffering a tape recorder from the rest of a sound system, and gain matching. It is certainly true that CD players, in particular, provide enough level from a suitably low output impedance to produce high-quality sound without additional gain or buffering from the preamp.

I could not fault the way the Line Drive performed with the electronics I currently have available, although there were a few cases where I would have liked more gain. I have, however, had CD players and tape units for review in the past where I felt the output was inadequate for anything but a preamp with high line-stage gain. I have also had equipment which does not interact well, particularly cassette players that require an active buffer, and units involving awkward differences in impedance.

Once again, the Mod Squad has an add-on active stage under development, but I have not evaluated it. Accordingly, you will need to be vary careful to make sure that your system will perform well with a passive control. You may find that even a few dB of gain can sometimes make the difference between a dull sound and a dynamic one, and that a slight loss of detail as the result of an active gain stage is better than buffering problems and tape recorder interaction, or the loss of timbre and dynamics from a major impedance mismatch.

If you use long interconnects, you will need to check very carefully to make sure your equipment has the right combination of input and output impedances to be used with a passive "preamp"—if source output-impedances are less than 1000 ohms and load input-impedances are more than 10k ohms, you should be OK with interconnects less than 2m in length, depending on their capacitance. Further, be advised that manufacturer specifications of impedance are often rather sloppy. Dealer assistance (if you can find one that knows what impedance means) is advised.

This raises the alternative of the PS Audio preamps, which also provide an affordable way of getting what is basically a passive high-level control center. The PS Audio 4.5, for example, sells for only $100 more than the Line Drive, but includes an excellent moving-coil/moving-magnet phono stage and a good switchable line stage. I have to say that, from a purist point of view, the passive components in the Mod Squad Line Drive sound very slightly cleaner. It is, however, a close thing, and I'd think long and hard about the choice. It may well be that the Line Drive is the better choice for a second system based around CD than as the "preamp" in the primary system for today's audiophile.—Anthony H. Cordesman



Footnote 1: Truly passive audiophiles should be aware that there is an $875 super version with WBT RCA jacks and Penny & Giles Conductive Plastic potentiometers.—Anthony H. Cordesman

Footnote 2: A point made, I think, by Martin Colloms some time ago, was that a device such as the Line Drive could be used to get the optimum sound from a high-level source such as CD, the user's existing phono preamplifier then being used to feed one of the passive preamplifier's other inputs.—John Atkinson

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Starman's picture

Still use my WBT version every day.

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