Предусилители — Nagra Reference Preamp

The Reference Preamp is a two-channel valve line preamplifier made in Switzerland by Nagra, established in 1951, whose engineering team has designed products for professional audio, national security and military use for more than 70 years. It updates the HD Preamp of 2017 with lessons taken from the Reference Turntable project, and it is built from separate chassis for the audio circuits and for the power supply. Owners can start with one supply and add a second one later.

Key specs that matter

Two E88CC new old stock valves, selected and tested by Nagra, form the gain stage. Five inputs are provided - XLR 1, XLR 2, RCA 1, RCA 2 and RCA 3 - plus a pair of bypass XLR inputs. Sensitivity of the two XLR inputs can be set to 1 V, 2 V or 10 V (Studio), RCA 3 offers 1 V or 2 V, and the first two RCA inputs are fixed at 1 V. Input impedance is above 50 kOhm. Output impedance is below 0.2 ohm at a -15 dB volume setting and below 40 ohm at 0 dB. Dynamic range exceeds 150 dB, and crosstalk is better than -130 dB at 1 kHz and -110 dB at 20 kHz. The audio chassis measures 438 x 396 x 121 mm, and preamp plus supply weigh 30 kg together.

Engineering and use context

The volume control works as two preamplifiers in one. The motorised left and right potentiometers on the front only set the level, and no signal passes through them - once a level is chosen, the audio is routed through a series of taps on Nagra-wound output transformers, so gain and phase match exactly between channels and no resistor sits in the signal path. The supply chassis generates a 200 V DC high tension, uses super-capacitors and custom-made capacitors, and feeds the audio unit through LEMO umbilicals with 9-pin analogue and 7-pin digital plugs. A phenolic layer inside the top cover adds damping, and adjustable feet with ceramic balls allow the chassis to be stacked. The modulometer, inherited from the Nagra II recorder of 1952, shows input or output level with 0 dB equal to 1 V RMS. A three-minute preheat runs at every switch-on.

Pairing

Nagra recommends the balanced XLR outputs because they are galvanically isolated, and names the Reference Amp as the intended partner, with the lowest input sensitivity setting suggested for Nagra sources. The XLR inputs are unbalanced unless optional hand-wound balancing transformers, made in Romanel-sur-Lausanne, are fitted. A REC/AUX RCA pair gives either a fixed recording feed or a variable feed for a subwoofer, and the bypass inputs let a home cinema controller drive the main amplifiers with the preamp switched off. Trigger jacks and a SUB-D9 port handle system automation.

Alternatives

The Nagra HD Preamp is the earlier two-chassis valve line stage on which the Reference Preamp is based.