Conrad-Johnson PV10 preamplifier Page 2
The power supply is realized entirely without the use of electrolytic caps; a handful of big-ass film caps replace the typical gaggle of power-supply 'lytics, a trait shared by all C-J gear. A medium-sized 16VA power transformer feeds a quartet of 1N4007 rectifiers in a full-wave bridge, while the rectified B+ rail is smoothed by two physically huge 20µF/630V SCR polypropylene caps and various small-value bypass caps before the discrete regulation stage.
Because of the single-ended nature of the power supply, the PV10A is AC-coupled at both the outputs of the phono and line stages with 2µF/450V SCR polypropylene caps. One layout detail that looked like it could be cause for concern was the closeness of the two line-stage coupling caps; physically large film caps like these 2µF SCRs can be fairly inductive, and the left- and right-channel output coupling caps are squeezed right up against each other. Only TJN and his merry band of measurements will know for sure, but I wouldn't be surprised if caps placed this closely together degraded the channel separation a bit compared to the Rec Out jacks.
In terms of tubes, a single 12AT7 and a pair of 12AX7s are used in the phono section, while a pair of the beefier 12AU7s are found in the line stage. RIAA equalization is realized with a passive filter network samwiched between a pair of tubed gain stages. The line stage is identical to the PV11's, with one difference: While the PV11's 2µF output coupling caps are bypassed with small-value polystyrenes, the PV10A's are not. Both the phono and line stages are direct-coupled to cathode followers, which reduce the PV10A's overall output impedance to under 800 ohms. While a bit higher than most solid-state preamps, this is much lower than the majority of tube preamps, and shouldn't present any interfacing problems with any high-end amps I'm aware of.
Be warned, Cherished Reader, that the PV10A's line stage is polarity-inverting and the phono stage isn't. This means that even though phono playback will be polarity-correct at the Tape Out jacks, both analog and digital sources will have an inverted polarity at the main outputs. This can be rectified by swapping the + and - legs of both your speaker cables at either the amp or the speakers' end, or—in the case of systems like mine where an active subwoofer precludes this kind of thang—flipping your CD player's or digital processor's polarity switch and reversing your phono cartridge leads, White for Blue and Red for Green (if the shield ground isn't connected to one of the pins).
Listening to music with the PV10A in the chain reminded me of nothing so much as listening to music with C-J's Sonographe SD22 CD player (which I reviewed in Vol.15 No.2). I said the SD22's "got the warm romance of tubes in spades," even though the Sonographe doesn't have a single tube in sight. Well, the PV10A's got five li'l tubes behind blue eyes, and the warm romance of tubes in spades, diamonds, clubs, and hearts.
When I first inserted the C-J preamp into my He-Man rig after several weeks of burn-in, I was struck by two things: 1) how much different the overall sound became when I switched to the C-J from either my own buffered passive preamp or the Melos SHA-1 headphone amp, and 2) how little the PV10A's immediately obvious colorations bothered me. In fact, I really enjoyed listening to music with the PV10A, even as I was aware of its not-too-subtle shortcomings. Unlike the problems of hardness and glare I hear with most inexpensive solid-state and digital gear, the PV10A never once sounded off-putting or annoying, instead sounding friendly, round, and without a trace of glare or grain.
In terms of basic character, the PV10A is closer to the "classic tube" sound than the best modern tube preamps. Warm and full through the bass and with highs tending toward softness, the PV10A evokes the romantic yet musical sound of tube preamps past rather than more strictly neutral designs like Melos's SHA-1 and ARC's LS2B.
But you know what? It held the music together. Even though I never quite reached the threshold where I stopped hearing what it was doing to the music passing through it, I found myself playing tons of records and CDs while the PV10A was in both systems, digging the music mightily and bathing in the fine, romantic, tubey sound. Just like the Sonographe CD player, the PV10A excels in communicating the raw emotional essence of the music playing through it, even while making obvious deviations from that ol' Straight'n'Narrow.