Solid State Preamp Reviews

Sidebar 1: Review System

Putting my customary preamplifier, the Krell KRS-2, to one side, the references used for this review were the $635 Audio by Van Alstine Super PAS (reviewed in October 1998), and the $659 PS Audio 4.6 (reviewed in September 1988 by Tom Norton) used with its normal external power supply, not the $469 M-500 upgrade (footnote 1). For reference purpose, the RIAA response of the PS 4.6 is Flat through almost the entire audio band, with a well-extended bass response, though it starts to roll off at the top of the top audio octave.

Power amplification was provided either by a 1986-vintage Krell KSA-50 or by a pair of VTL 100W monos, these sitting on Mission Isoplats. Loudspeakers were the Celestion SL700s, used on their matching stands; source components included my stock Revox A77 for master tape replay, Marantz and Precision Audio CD players, and the fully loaded Linn LP player (Sondek/Ittok/Troika) sitting on a Sound Organisation table; interconnect was either Monster M1000 or Tiare solid-core silver; speaker cable was Monster M1, two runs being used to bi-wire the SL700s.

As well as being used as the main system preamplifier, bypass testing was carried out with each preamplifier set to unity gain at 1kHz (harder said than done with the stepped volume control of the Parasound) and inserted in the tape loop of the PS Audio 4.6, used in its "Straightwire" mode so that no other active circuitry could impose its signature on the sound. I first used the Ben Duncan PAS-01 passive control unit for bypass testing, but changed to the PS because it will be more readily accessible to readers wanting to repeat these tests. (The high input sensitivity of the VTLs made it easy to achieve adequately high listening levels, despite the absence of any line-stage gain.)

A note on the auditioning of the preamps' phono inputs: not being familiar enough with the sound of any current MM pickup to be confident about using it as a reference, I decided to stick with the Linn moving-coil (footnote 2). The Parasound, therefore, could only be auditioned with the HFN/RR Black Head transformer in the signal path, which could be thought of as putting this preamp at a disadvantage compared with the other two preamps I review in this issue, which do have MC inputs (footnote 3). I reassure readers, however, that I carried out checks by also auditioning the MM inputs of the other two preamps with the Black Head in-circuit, and also by conducting bypass tests on all three with the CD player driving the phono inputs via an Old Colony inverse-RIAA network. My comments on the sound of the three preamplifier phono inputs are based on an amalgam of this complete auditioning.

I need hardly add that the playback levels were matched for all the comparisons, removing volume discrepancies as a source of subjective differences. Audiophiles who don't practice such good housekeeping for their tests should be sentenced to a diet of Tiffany recordings until they learn to mend their ways.—John Atkinson

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Footnote 1: I found it interesting to compare this large-company product with one from a supposed "tweak" company, PS Audio, and not just regarding sound quality. (Though I emerged from the lengthy listening sessions with more than a little respect for the Californian preamp's sonics.) The PS 4.6 appeared to be the best-made of the four solid-state models, contrary to what you might have been led to believe, given the high end's traditional reputation for assuming that excellence in sound quality will always compensate for shoddiness of design and manufacturing.

Footnote 2: As pointed out by JGH in his follow-up review of the Threshold SA-1 power amplifier and Sound Lab A-3 loudspeakers, changing two variables at once leads only to sonic confusion. It is essential when reviewing any component to ensure that it represents the only change made to the system.

Footnote 3: Parasound's Richard Schram recommends the Denon AU-320 transformer if the P/FET-900 is to be used with an MC cartridge. Although I do possess an example of this classic step-up, as luck would have it, it is still in storage in England.