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Returning to the NAT Symmetrical, it offers six inputs each, all of which accept balanced or single-ended feeds. Just remember to change the right front panel XLR/RCA switch depending on what input connection you wish to use. If you have the switch in the wrong position (say on XLR when listening to a single-ended source), signal will pass but the sound quality will be degraded. I tried it both on purpose and by mistake and you'll notice. Imaging, bass control, tonal density - everything will be askew. This is the smartest and most convenient solution I have seen so far to provide such large input flexibility (the input adaptors of the SMc VRE-1 were pretty smart and convenient too but come at an additional cost). The only downside -- but it is minuscule -- is that when you change the position on the XLR/RCA switch, the machine undergoes a 30-second reconfiguration cycle. Unless you are a very impatient audiophile, you won't notice. But then impatient audiophiles would probably not even consider tube electronics in the first place.

A similar but longer 1-minute soft-start cycle happens when the Symmetrical is first turned on. You should wait another fifteen to twenty minutes before any critical listening to let the tubes warm up and settle. The NAT already sounds very good after the first five minutes but it does not reach stellar until a little later. It would be a mistake to judge it too soon.

I already mentioned the volume control system but it deserves a few more lines. Typically superior balanced preamplifiers use stepped attenuators as the only efficient way to closely match the attenuation level between the two phase legs of each channel. The obvious problem with stepped attenuators is that they are stepped. If the steps are too big or insufficient, it can be hard to find the proper listening level. The NAT Symmetrical differs. Its volume control is composed of a series of relay-activated matched resistors. The volume knob only acts as an indicator while a logic circuit switches resistors in and out of the signal path to provide the desired attenuation degree. This offers far more steps than conventional stepped attenuators but with the same precision. The only downside is that each time you change volume, you'll hear relays click and the sound coming in and out as the relays close the circuit again (a very fast phenomenon but the sound goes away for a split second before coming back at the revised level). More than an inconvenience, it is something that takes a little time to get used to. At first it bothered me, then I forgot to even pay attention.

There are however a few 'features' that need to be reiterated as they could be deal breakers depending on your desires and sensibilities. Pretty low on the itching powder list is the fact that this design uses twelve tubes and does heat up quite a bit. That's no big deal in winter and then actually fairly welcome but when temps rose to 80° last week inside, I was not unhappy to switch back to a transistor preamplifier - until I played the first disc of vocal music that is. It instantly reminded me why I love the NAT so much.

Slightly more annoying is the rarity of some of those twelve Russian tubes (4 x 6N6P, 2 x 6X4, 2 x 6N2P-EV, 2 x OA2, 2 x 6N1P-EV) and the fact that you can't retube this beast at any one US tube dealer - nor using two or three. I searched the online inventories of all the major hifi tube vendors in the US. Between all of them, I could not scare up a full set of tubes for the NAT Symmetrical. That leaves retubing through NAT and their US distributor as the only viable option which they also favor for reliability and consistency. Since NAT has been operational for sixteen years, it probably is not too risky a proposition but I like freedom of choice better still. That's a French thing.

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Most annoying is the phenomenal (and I mean it) thump this preamplifier makes at power down. It is so loud and violent that I feared I'd blown up one or both speakers the first time it happened. You can avoid this by muting the Symmetrical before turning it off but it is also easy to forget after a late night listening session and the reminder is far from pleasant. If I had only one thing to change in the Symmetrical, it would be the inclusion of an auto-mute turn-off. My 86dB sensitive FJ OMs survived the shocker but I wonder how more fragile high-efficiency drivers would react.

Initially the NAT Symmetrical also developed a serious case of hum and buzz in single-ended mode but a little trouble shooting revealed it innocent. It merely was the recipient of a ground loop between the Esoteric X03SE source and the Hypex bass amplifiers in the Genesis G7.1f speakers. A pair of Isotek power conditioners took care of this very elegantly (a Titan for the G7.1f woofer amps and the superb Nova for source and preamplifier - I intend to follow up on these devices shortly) by breaking the ground loop and improving overall operational silence and stage depth.

While on power requirements, I tested the NAT with four different power cords - Zu Mother, Accustic Arts Ferrite II, NAT AC Coupler Black (normally dedicated to power amplifiers or other high voltage components) and NAT AC Gray (recommended for preamplifiers and other low consumption components). It won't come as a surprise that the NAT AC Coupler Gray was the best match for the NAT Symmetrical. It opened up the treble and increased resolution while maintaining a tight and articulated bass. The NAT AC Coupler Black was more similar than different but its treble-enhancing power went further still to get excessive on certain records. The Gray hit the right balance for me. The AA Ferrite II was warmer and more 'tubey', not a bad match but this type of midrange reinforcement was unnecessary with the NAT yet worked wonders with the Esoteric C03. As experienced with the AA preamp and the C03, my previous Zu Mother reference proved the dynamically most limited by not allowing the full potential of the gear to express itself.