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REF10 Nano

This review first appeared in March 2024 on By request of the manufacturer and permission of the author, it is hereby syndicated from the German original to reach a broader English audience. Ed.

Writer: Nick Mavridis
Analog sources: Thorens TD-316 MkII with Nagaoka MP-110
Digital sources: Lavry DA-11, Merging Technologies HAPI (AD/DA converter), Rega Apollo

Integrated amplifier: Rega Mira
Power amplifier: Abacus Electronics 60-120D Dolifet
Loudspeakers: Harbeth Super HL5 Plus XD, Genelec 8010A, JBL Control 1C, Piega TMicro 5, Vogel Custom Blue, Vogel Custom White
Listening room: 51m², 2.3m ceiling
Review component retail price: €1'999

Clocking significantly influences digital-to-analog conversion's quality. Like a metronome, it determines at exactly what times the data stream conversion is clocked. The more precise this process is because the clock's beat fluctuations diminish, the better the result. This clock function usually implements in our digital devices themselves but there are also external reference clock generators like today's Mutec REF10 Nano. It's the Berlin firm's latest 10MHz clock generator. At €1'999, it's significantly cheaper than their REF10 or REF10 SE120 we reviewed already. While a conventional word clock equals direct sample rate, Nano outputs 10MHz significantly beyond all PCM sample rates (only DSD occurs in the megahertz range). The advantage of 10MHz generators is, among other things, higher accuracy and above all, lower phase noise. 10MHz clocks originated outside our hifi sector. They show up in telecommunications systems and in GPS satellites where they have a direct influence on positional accuracy.

Mutec maintain a list of currently available audio devices with 10MHz clock inputs here. For devices without dedicated 10MHz port, prior clock signal conversion to a standard audio sample rate is necessary. So Mutec provided me also with a €1'399 MC3+ USB whose full title Synchronizable Digital Audio Master Clock & Audio Re-Clocker & USB Interface says it all. The Mutec MC3+ USB can do a lot, especially reclocking, but my test of Nano largely limited this 2nd device to converting Nano's 10MHz clock output to 44.1 – 384kHz clock signal.

Although caesium and rubidium aka atomic clocks exist, Mutec argue that they shine more where long-term stability rules supreme. Across the ultra-short time range relevant for audio, team Berlin see so-called OCXO as having the advantage because their pulse-to-pulse deviation aka jitter is particularly small. OCXO is short for oven-controlled crystal oscillator and preheating the clock in a controlled environment eliminates subsequent fluctuations due to ambient temperature changes. Nano's measurement values are more than impressive. As a proper German engineering-first company, Mutec refrain from exaggeration and embellishment to publish honest and comprehensive test data. Their figures on frequency stability, phase noise and aging should be beyond doubt. Their clock output tracks a strictly symmetrical square wave signal. According to Mutec, theirs is blessed with particularly steep slopes and very low overshoot to minimize clock jitter for better sound.

As befits a masterclock, Nano needs few controls. The 'select' control activates individual BNC sockets, two at 50Ω, two at 75Ω. Those expect cables of matching characteristic impedance to avoid signal reflections. Mutec's list itemizes this impedance where known, otherwise inquire with the maker of your kit. The power IEC accepts 85 to 305VAC at 50/60Hz. Alternatively there's a 15VDC port for an external power supply. Next to the frontal power switch we see two LED for which power source is active. The 'ready' LED tracks the OXCO's warm-up protocol which takes ~5 min. to achieve frequency stability. All this was well and good but how about sonic effects? My Rega Apollo CD player lacks a clock input but I had a variety of other components to compare their internal to Mutec's external clock via the MC3+ USB then with/out upstream Nano.