Pre/ Power Amplifier - Nagra Jazz/ MSA (Part 1)

5/7/2013 6:40:43 PM

Ringing changes for the famous Swiss manufacturer is Nagra’s latest Jazz tube preamplifier. We’ve tested it with the company’s compact MSA MOSFET power amp.

Yes, they’re expensive but Nagra’s electronic jewels are gloriously timeless and beautifully engineered. In 2011 Nagra celebrated 60 years since the company founder Stefan Kudelski had invented the first Nagra I portable tape recorder: a milestone marked with the introduction of new 300i (integrated) and 300p (power) amplifiers employing 300B vacuum tubes.

No sooner was our review of the 300i published (HFN Dec ’11) than major corporate changes were announced, the specialist audio division becoming a separate entity from the giant Kudelski Group at the beginning of 2012. And last summer’s High End exhibition in Munich saw the first fruit of the reorganized Nagra firm: the Jazz preamplifier featured here.

Family genes

Drawing its name from the brand’s sponsorship of the annual Montreux Jazz festival, it maintains the compact form factor and familiar brushed aluminum casework synonymous with the marque – it’s Nagra through and through. But it is a tad more conventional than the PP-L and PL-P preamplifiers it supersedes, with in/output sockets at the rear rather than on the side-cheeks (an inheritance from the company’s professional gear).

And Nagra says the new preamp’s circuitry which employs 2x12AX7/ ECC83s and 1x12AT7/ ECC81 dual-triode values has been completely rethought to improve stability and reduce noise to the point where its engineers no longer consider a battery power supply a necessity. The Jazz is powered by a hideaway PSU that delivers DC to the main unit via a cable terminated with a Lemo connector.

Exquisitely constructed inside and out, the Jazz, direct-coupled to RCAs and transformer-coupled for balanced operation through XLFs

Exquisitely constructed inside and out, the Jazz, direct-coupled to RCAs and transformer-coupled for balanced operation through XLFs

It has five line inputs labeled A-to-E, four of which are single-ended (RCA) while input ‘A’ uses XLFs. When the preamp is in its standard form, this XLF input is asymmetrical. But as you can see from our photograph below, provision has been made within the chassis for optional input transformers to be fitted, to provide symmetrical (balanced) operation if desired. Robert Prubell of UK distributor RT Services expects this option to be available in a few months’ time, at a price that’s yet to be determined.

As with the transformers used for the preamp’s balanced output, they will be made in-house at Nagra’s factory in Romanel-sur-Lausanne. There’s also a unity gain pass-through provided on XLRs (labeled input ‘F’, accessible only via the supplied remote control handset) that remains active even if the Jazz is turned off. This pair of ‘bypass’ XLR input sockets is connected directly to the preamp’s XLR outputs without going through the output transformers, so if the source is balanced, the connection remains balanced all the way through.

A small switch on the fascia, next to the rotary input selector, toggles between Output 1 (balanced, LFRs) and Output 2 (single-ended, two sets of paralleled RCAs for easy bi-amping), while the switch next to it changes the internal gain (unity or +12dB). Stereo/mono and Mute switches are also featured, together with Nagra’s trademark Modulometer, the brightness of which can be adjusted in seven steps. Red and green needles indicate the output levels of the left and right channels respectively (yes: I too would have expected red/to be the right channel.

Fun with the remote

The supplied remote looks very similar to the handset used by the Solution brand (also Swiss) and it’s an exemplar of sensible ergonomic design that fits comfortably in the hand. One’s thumb falls naturally on to up/down and left/right keys (of the type typically used for menu navigation in DVD/ DB players), the former driving the Jazz’s motorized volume control, the latter the balance pot, while what would be an ‘enter’ button in the center is used for Mute. Additional keys below control power on/off and provide direct input switching. It’s a hoot switching from, say, input A to input E using the remote and subsequently observing the motor-driven mechanical input selector automatically whir and click through the inputs…

Unmistakably Nagra, the fascia sports the company’s trademark Modulometer. Gain balance and input selector are motor-driven

Unmistakably Nagra, the fascia sports the company’s trademark Modulometer. Gain balance and input selector are motor-driven

Nagra is currently working on the design of a new solid-state power amplifier which will be released much later in 2013 so, for this review, we’ve paired the new Jazz preamplifier with Nagra’s MSA power amp introduced in 2009. Rated at 60W/8ohm it employs just a pair of MOSFET for each channel (MSA standing for MOSFET Stereo Amplifier) in a deliberately simple, fully balanced circuit arrangement. The output devices are coupled to the amplifier’s substantial top-mounted heatsink which is milled from an aluminum block. Even driven hard the unit barely gets warm. In keeping the amplifier so compact, Nagra employs a sophisticated switch-mode power supply, albeit featuring a hefty toroidal transformer. Incorporating Power Factor Correction that Nagra first championed in its pyramid-shaped STA. MPA power amps a decade ago, the supply employs Linear Technology controller chips (one for each channel), the design of Nagra’s active feedback supply aiming to provide efficient energy transfer and decoupling between the supply and amplification stage.

MSA power amp features a substantial top-mounted heatsink. The power selector switch includes a signal-sensing ‘Auto’ position

MSA power amp features a substantial top-mounted heatsink. The power selector switch includes a signal-sensing ‘Auto’ position

A pair of white sockets located between the two sets of gold-plated WBT speaker terminals at the rear is for plugging in a supplied jumper to bridge the amplifier’s two channels and double its output power. A three-position switch selects between normal stereo operation, bridged mono, or ‘double mono’ whereby each channel is entirely separated for bi-amping a loudspeaker. Two further switches (one for each channel) select 1 or 2V input sensitivity of the MSA’s single set of balanced XLR inputs. Nagra thoughtfully includes a pair of Neutrik XLR-to-RCA adapters for connecting preamps with single-ended outputs. An Auto (signal sensing) option shuts down the amplifier after approximately 15 minutes.

Kudelski connection

Over the decades, the Swiss firm founded by Stefan Kudelski has grown into a $525m turnover corporation employing some 3000 people. The specialist audio division, responsible for designing and manufacturing professional equipment and home hi-fi components, has represented only a small part of its global operations. The Kudelski Group’s main activities today are in the fields of cyber security: hi-tech electronic access and security systems, and encryption/descrambling systems for digital broadcasting networks. Stefan’s son André succeeded him as Chairman and CEO in 1991. In January 2012 the Nagra audio division became a separate entity, still with close family ties, under the new name Audio Technology Switzerland. Stefan’s daughter Marguerite, who holds a PhD in micro technology, is the new ci-owner and is heading up research and development, along with brother-in-law Pascal Mauroux, an engineer and MBA graduate who has had an international career with Nestlé and Nespresso.

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