Beyond the Jazz.
The second thing to strike the observer is the power supply; or rather, the apparent absence thereof without traditional power toroidal transformer and rectifier. With Nagra being long-time experts at switching supplies and given how demonstrably eclipsing the Jazz would have to start by lowering the S/NR to better than -125dB—a circuit's sound of silence which determines what dynamic range it can express—the Classic adopts a medical-grade Swiss SMPS to go where a linear supply in such close proximity to signal-path circuitry couldn't. To reduce operational heat, shorten signal paths and lower power consumption meant simplifying and stripping down all circuits. Shorter signal paths benefitted their immunity to disturbances and radiation which again helped lower the noise threshold.

"The four-layer gold-plated glass-epoxy military-grade PCB were chosen according to the most rigorous criteria in terms of tolerances, durability, reliability and listening performances. A ground layer screens out disturbances, radiation and avoids static loops and hum. Ribbon cables ensure that the paths between PCBs are as short as possible. The motherboard mounts on elastomeric silent blocks to filter out mechanical vibrations. Versus the four small circuits and connecting wiring of the Jazz rear panel, the Classic solders all of its i/o connectors, sealed selector relays and balanced-to single-ended converter to a single large back-panel board without any wiring. The single-ended topology distributes all odd and even harmonics of the audio signal whereas a balanced circuit cancels all even harmonics and only works with odd harmonics, meaning you have to locally inject some negative feedback to compensate. All inputs are floating to allow the signal to be managed in pseudo-balanced fashion until it reaches the gain stage. Each input is filtered to eliminate RFI with a combination of inductances and capacitors. High-quality sealed relays switch the inputs such that only the ground of the active input connects. All other grounds are lifted to prevent static loops between any inactive sources. The XLR bypass direct-connects the input signal to the output bypass XLR in true balanced configuration even when the Classic is disconnected from the mains.

"The CPU management board, LCD display and rotary controller add functionality beyond the Jazz like English/French display, full alphanumeric input naming with up to 8 characters, ±3.5dB balance offset in 0.5dB increments, stereo/mono conversion and assignation of non-Nagra Philips RC-5 formatted remotes." Taking full advantage of their new software, Nagra have moved the serial number to it as well as elapsed tube time (resettable) and total operational time (not changeable). Also, "the Classic Preamp embeds far more parts than the Jazz did. A large part of them are made for Nagra under very strict specifications. Where the Jazz still employed some electrolytic capacitors at critical locations in the audio circuit like interstage coupling, high voltage bypass and component decoupling, the Classic Preamp only using polypropylene capacitors custom made for us by SCR. The valves provided are subject to the most rigorous selection and testing, burnt in for 48 hours, then individually measured and sorted for gain, hum and microphony. At the end of the test, more than 60% of tubes are rejected, with the remaining ones paired up for tightest matching.

Headphone amp gain jumpers in default max-gain position. Moving the '10' jumpers to '6' creates 6dB of cut. Low gain is achieved with a single jumper per channel in the '8' position.

"The first stage of the circuit is built around one 12AX7/ECC83 double triode per channel. The two triodes of each bottle are biased in class A and tied together in a differential anode follower topology for stability. The second stage where most of the gain is generated goes to a type 12AT7/ECC81 double triode, with one half per channel in a class A cathode follower arrangement and some local negative feedback for very low output impedance and very low distortion. The signal out of the cathode then couples to the outputs through a custom-made polypropylene capacitor. According to the 0 dB or 12dB position of the front-panel gain switch, a relay arranges a set of resistors that adjust the gain of the 12AT7/ECC81 stage accordingly. The headphone amplifier is based on ultra high-performance high-speed circuits with noise and distortion reduced to extremely low levels. This circuit acts as a solid-state current buffer behind the tubes. There are no capacitors in its signal path and a servo permanently maintains precise 0V DC from any constant voltage across the output. The circuit allows for choosing an output level by means of jumpers."

In use, the display confirmed the 2.5-minute high-voltage delay with heating to track the properly glacial Swiss rise for extended parts longevity. Once live, I checked on elapsed tube hours. Being the original set, that would be the same as the total odometer reading. The menu's about layer showed how Nagra had pre-clocked 1'400 hours of break-in. Because I could, I now used the convenient push/rotate controller knob in edit mode to, in all caps for my older eyes, name the XLR input Aqua XLR, the first RCA input Aqua RCA for our Aqua Hifi Formula DAC. And as if the headphone gain jumpers weren't enough, I learnt that the preceding tube stage's 0/12dB function also affects the 6.3mm headfi socket. This makes for a most convenient on-the-fly trim. At 12dB and with the internal jumpers at default, HifiMan's Susvara had headroom to spare. Witnessing that the Classic Preamp could power those samples of the 83dB inefficient sort with full authority was an unexpected but most happy wakeup call. It instantly telegraphed that far from being a convenience feature to keep up with les Joneses, Nagra's headphone port meant serious business. This warranted a full sonic inspection. In fact, it warranted starting out my auditions in headfi mode. For that appointment, enter the Susvara planar, Final Sonorous X dynamic and D8000 planar and finally Sennheiser HD800 dynamic as a high-impedance example. As the photo shows, the Classic's top panel sports strategic little dimples to receive the ball-bearing footers of various docking mates like Nagra's CDP represented by our Jazz. With this scheme, two or more Nagra components stack solidly and perfectly aligned. It also shows how the Classic Preamp's length does rather exceed the original footprint. Finally, the Classic inherited the Jazz's fabulously ergonomic remote but changed to a stronger two-tone scheme, with the casing's black migrating also to the face.

Susvara. Loudness isn't the same as proper control. Just because an amp makes a headphone go loud enough doesn't mean the sound quality is at its fullest potential. For Susvara, my giveaway is bass power/texture relative to our in-house references like Bakoon's AMP-12R; and in balanced drive, two Questyle CMA-800R monos or COS Engineering's H1. Of those, the current-mode Bakoon with its ultra-wide bandwidth and concomitant speed is our ultimate designated Susvara driver. It helps determine how much or little another amp might leave under the table by not extending into the bassment with the same power, pitch definition or damping. With even 'no gain' still creating matched levels well before maxing out the attenuator, here the 0/12dB switch's dissimilar NFB showed a difference. On hard-hitting multi-layered ambient fare between Robert Miles and Indian percussion ace Trilok Gurtu, 0dB had more slam and bite, 12dB more weight and bloom. That made for a trade-off between greater body and elasticity (12dB) versus slammier drier bass (0dB). This wasn't limited to the low frequencies of course. Once I gravitated to mellower acoustic fare, I preferred 12dB's slightly more redolent behaviour. For extreme studio trickery where expert DJs like Mercan Dede erect capacious soundstages with many layers atop true infrasonics, I preferred 0dB's drier separation. This and how much of a shift will translate will vary from load to ancillaries to listener. The takeaway is simply to view this control as also a minor potential gestalt shifter. It can be more than just a gain switch.

Note 12dB's actual volume setting. This created standard SPL for the Susvara. Even loudness fiends should have sufficient headroom.

Relative to our transistor headphone amps driving Susvara, the Classic's tube contributions were unmistakable. They passed through the solid-state current buffer like a tunnel that has zero impact on any cargo you run through it. Akin to dim-sum finger foods on a spinning platter, the flavours of density, tone weight, colour intensity and more subjective reverb moved into the foreground whilst separation, depth of field and chiseled outlines moved back. Nothing dropped from view but these aspects changed their relative position on my sonic table. That was expected. If the tubes were sonically inactive, why use them in the first place? Not expected was the ability to reproduce certain manufactured high cracking/crinkling sounds on the Miles_Gurtu album with all their familiar hardness, incisiveness and zing intact. This spoke to unfettered rise times and a fully opened-up treble without cloud cover. Likewise for the low bass. Though fatter and texturally more redolent, it showed no reduction in reach. On impact in fact, the body gain conveyed more, not less pugilism. Clearly this valve circuit could do techno brutality and not go unduly soft even into a very challenging but also very quick, lucid and wide-bandwidth load. How would the innately more sonorous and bassy Finals fare?