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Reviewer: Srajan Ebaen
Source: Zanden Audio Model 2000P/5000S
Preamp/Integrated: ModWright SWL 9.0SE; Bel Canto PRe2
Amp: First Watt F-1; First Watt F-2 [on review]; 2 x AudioSector Patek SE; Canary Audio CA-308s [on review]
Speakers: Zu Cable Definition Mk1.5
Cables: Zanden Audio proprietary I²S cable, Stealth Audio Indra (x2), Zu Cable Birth on Definitions, Zu Cable Ibis; Crystal Cable Reference power cords; ZCable Hurricane power cords on both conditioners
Stands: 1 x Grand Prix Audio Monaco four-tier
Powerline conditioning: 2 x Walker Audio Velocitor S
Sundry accessories: GPA Formula Carbon/Kevlar shelf for transport; GPA Apex footers underneath stand, DAC and amp; Walker Audio SST on all connections; Walker Audio Vivid CD cleaner; Furutech RD-2 CD demagnetizer; WorldPower cryo'd Hubbell wall sockets
Room size: 30' w x 18' d x 10' h [sloping ceiling] in long-wall setup in one half, with open adjoining living room for a total of ca.1000 squ.ft floor plan
Review Component Retail: $1,995

Positively vomiticious. That's how some uncompromising designers view the variable resistor. Think affordable Japanese Noble or Alps potentiometer in translation [right]. Unless you assemble your system such that your average playback levels perfectly match the overall gain structure of running a fixed source direct into your amps -- and you put up with the uncontrollable variances of recorded signal strength from CD to CD -- you need to control your audio system's volume. The most common solutions are so-called carbon or plastic-based pots. Another one is the chip-based attenuator by companies like Burr-Brown (as found inside my Bel Canto Design PRe2, for example). Considered a step up from the mechanical wiper-based pots are resistor-ladder types. GoldPoint [lower right] and DACT are two of the most well-known makers of such devices. They segregate the non-stepped smooth range of a wiper-type attenuator into discrete steps. Each step is fixed by a single resistor. The volume jumps from step to step. The size of the in-between gaps is determined by how the resistor values are staggered (usually in 1 to 2dB steps over the range a preamp designer assumes will be the most commonly used, and in 3dB or larger steps below and above that). The rare audio designer like Charles Hansen of Ayre Acoustics will, for his K-5xe preamplifier, even go through extreme lengths to design and build his own volume control "actuated by a silky smooth optical encoder, using FET switches and precision metal-film resistors" to avoid the compromises associated with commercially available volume control solutions.

A purist but expensive alternative to resistor-based attenuation is using a transformer to convert an incoming high-voltage low-current signal into a low-voltage high-current equivalent. Instead of discrete resistors to form the ladder, this uses discrete transformer secondaries that are hard-wired to a stepped rotary switch very similar to the more common stepped attenuator. The most famous proponent and example of this approach is Audio Consulting's ultra-tweaky Silver Rock from Switzerland [upper left]. As a remote-integrated, less tweaky iteration, there is Dave Perry's Advanced Vacuum Tube Audio Concepts' $6,858 Pasiphae, wonderfully reviewed by Ross Mantle in UltraAudio [middle left]. Transformer-based attenuation is a form of passive signal manipulation but vinyl step-up transformers remind us how it could be configured for actual gain. Most consumer-based transformer attenuation is based on Stevens & Billington autoformers from the UK. Those are in fact in evidence inside the Pasiphae as well as John Chapman's Bent Audio TAP, the Level-2 $1,095 Django preamp [lower left] and the Music First Audio unit. The Sonic Euphoria single-ended or balanced preamps also use autoformers, albeit of unspecified origin (off-the-shelf units are available from Antique Sound, Dave Slagles and DIYHiFiSupply). The genre in general has become known as TVCs: transformer volume controls.

S&B is also what's at the heart of Peter Daniel and George Tordai's AudioZone PRE-T1: a TX102 magnetic volume control which operates at or below unity gain but can be configured for 6dB of additional gain. From the UK website: "The TX-102 is a ... multi-tapped transformer designed to be used with a 20 position switch or with relays [the Pasiphae implements it with reed relays - Ed.] ...
The primary application is in so-called passive preamplifiers, more precisely passive control units... Whilst 'passive preamplifiers' initially created notable interest as a sonically extremely pure method of controlling volume and selecting inputs, they have soon faded back into obscurity, not surprisingly as most of these devices suffered from substantial impedance mismatches with either sources or loads."

If for example a 5KOhm resistive volume control were to be employed in a passive control unit, the source would be required to at all times drive a quite severe load of 5kOhm. If combined with a 1KOhm source impedance, the worst case output impedance would be 1500-ohm at -6dB attenuation while at -20dB, the output impedance would still be around 540 ohms. If combined with around 1nF load capacitance (easily found in longer, high capacitance interconnects), this leads to a 0.3dB attenuation at 20kHz for a 20dB attenuation setting, practically showing the absolute permissible limit for load capacitance. The worst-case attenuation at 20kHz almost reaches 1dB! If, to provide our source with an easier load, we choose a 50 kOhm resistive volume control, we must either accept drastically higher levels of rolloff at 20kHz or we must limit the load capacitance to less than 100pF. Such a level of capacitance (100pF) can easily be found with only 1m of high quality interconnect cable and is often exceeded by the input capacitance of many amplifiers!... With all transformers, the ultimately realized output bandwidth is very much system and application dependent but the bandwidth-limited TX-102, when driven from a sufficiently low impedance (1kOhm or less), will provide a usable bandwidth of at least 10Hz to 100kHz (+/-1db) or better "

Transformer-based attenuation is not only preternaturally quiet (passive) but can additionally minimize ground loop issues due to the decoupling action of the transformer's air gap. Perhaps most attractive about the entire concept is the gain in dynamic resolution at low volumes. The "unused" portion of the incoming source signal isn't thrown away as heat (resistor-based attenuation). It's converted to current, insuring better amplifier drive. To make TVC work requires that your source can drive your amplifiers to full output directly. That means no additional gain. Most digital sources put out 2 volts and most amplifier input sensitivities reside well below that. Hence this prerequisite is automatically met most of the time. However, exceptions could exist especially in micro-power amp contexts. Then a preamp becomes an active gain stage that works above unity gain/input voltage. There the switchable 6dB boost of the PRE-T1 might be insufficient.

Now allow me a mini detour. In the wake of my Patek SE review, I'd sent an e-mail to my writers. The cryptic subject header "your Editor just joined the dark side" was a dramatic ruse to capture the attention of my jaded audio hacks. In the actual e-mail, I joked about having finally joined the amplifier sand brigade but how my continued reliance on the tubed ModWright preamp meant I hadn't completely lost it - yet. Picking up on that tiny opening with the nose of a born trouble maker, Paul Candy on staff opined by return e-mail that if I just gave Peter Daniel's matching preamp a listen, I might well swear off tubes for good. Needless to say, such a challenge could not unanswered go. Within minutes of digesting it, I rang up George Tordai in Canada to inquire about a review loaner. After sharing how a Hong Kong reviewer had just absolutely raved about the unit (the review unfortunately hasn't been translated yet for broader -- i.e. moi -- consumption), he admitted that he and designer Peter Daniel were currently at a loss to decide which they liked better, the copper or silver version of the transformers. According to George, the copper iteration sounds very much like tubes whereas the silver offers even more detail and soundstages differently (and would have to cost more).

Couldn't they offer both? That indeed might be in the cards. For now, all I know is that at least one PRE-T1 will shortly arrive in Arroyo Seco for my inspection. Which flavor I shall have to discover. Should two arrive, I'll even be able to report on the differences. The stock rear apron is wired for two inputs and two outputs but can also be ordered as three inputs and one output if bi-amping or subwoofing aren't desired. A 24-position Elma switch selects from the transformer windings and "dual mono" two-pole toggles select the input. A ground lift and 6dB gain switch round out the features.

Candyman needled further in a subsequent e-mail by first buttering me up, then following up with a sucker punch. "Btw, you nailed the Patek. Peter's stuff is the shit. He gets better and better every year. I'm seriously thinking of buying the preamp, as funds permit of course, then eventually spring for the monos. To date, that's the best I've heard, tube or SS." Geez, I shoulda hired yes men instead of putting up with this type of insubordination. Not! The funnest part of working with my team of reviewers is the variety of their opinions and the constant reminders this elicits - on how endless the ways are to achieve musical satisfaction (and how there's often more than one soul mate per listener). Added Edward Barker, "from my perspective, it's always the tube preamp that is key to a good sound. From then on, there are several interesting options." All this by way of setting the stage. Having reviewed Jeff Hagler's Sonic Euphoria TVC preamp -- albeit in a system context that's quite changed since -- I know from personal experience that the dynamic expander function of this approach is very real indeed. My question was, would I be able to do without the small signal tubes in my ModWright now that the non-tubed Patek SEs had become my chosen big-rig amps?