Cees Rujtenberg’s Metrum Octave, Hex and then MK2 Octave have made quite the splash in DAC circles these past few years. And rightly so – each model has contributed to redefining what’s possible at their respective price points. The undisclosed nature of each model’s ‘industrial’ decoding chips has helped to keep the whodunit mystery going and Rujtenberg’s attention to detail with the Hex’s internally powered m2Tech OEM module showed that not all USB implementations are born equal. The Hex’s (optional) USB input was up there with Audiophilleo1/2 and Resonessence Labs Concero/HD S/PDIF intervention.
Given Metrum’s recent-ism you’d be foregiven for thinking that our man from the Netherlands is a relative newcomer. That his DACs sound so good out of the gate gives lie to Rujtenberg’s pedigree: he’s been in the audio business for knocking on 25 years, a little factoid that only came to light when first perusing a new Metrum flagship DAC – the Pavane.
For this even bigger fella, Rujtenberg has foregone the secret ‘DAC’ chips of old and begun brewing his own. He’s now building his own chips and the Pavane will sport 8 R2R converters per side, divided equally among 4 modules.
Parallel-driven R2R ladder networks ensures their handling of very high sample rates. For the corresponding high-speed output, super swift IV conversion is also deployed.
“Do you have any photos of the DAC ‘chips’ or have you sealed them into modules to protect you IP?”, I asked Rujtenberg via email.
His reply: “I was working a full year on it and a bit scared to show it to the world therefore the units are completely sealed. As it was quite an expensive exercise they are also available for OEM.”
And then more on the R2R ladder chip’s workings: “First we have the serial to parallel conversion. The chip handles several formats like RJ24 and I2S and is realized by some logic which translates the serial data to parallel data. These data is supplied to the R2R ladder. The dac is available as current out or voltage out version. The voltage out version is using an I/V section having a slew rate of 1500 Volt/sec. After this circuit a second order passive filter is used and starts at 65 khz.”
In the engine room, every DAC engineers new favourite toy – an FPGA. Rujtenberg has coded his as a ‘forward correction module’, which reportedly splits up the audio samples for each channel into new separate data streams; that’ll no doubt do good things for channel separation (reportedly 120dB). Yes, the Pavane is dual mono
“Each DAC cluster processes a portion of the data in the most linear region of the DAC chips. The result of this process is an extremely high linearity, right down to -140 dB, which gives the Pavane a realistic 24 bit dynamic range.”
Rujtenberg elaborated in a follow up email: “The FPGA splits the dynamic range in two sections and will feed them to the two DAC clusters available on each mono board. Assume that we have a very low level signal in the digital domain , in normal cases this should be supplied to the lower part of the R2R ladder network. This approach leads to noise and linearity errors. In our case this part is sent from the FPGA to the uppermost part of the R2R ladder of the second dac cluster which leads to a very high output and will be present in the most linear part of the DAC. The next step is to combine both outputs coming from the two dac clusters in the analog domain. To bring back the original low signal we should attenuate it until the right level is back again. The result is a extreme linearity down to -140 dB. Switching noise as always present coming from the ladder switches will be attenuated as well and is on an un measurable level of -170 dB.”
The Pavane promises considerably more serious casework than the Hex in order. Heavy aluminium front and side panels and a double-damped inner frame seek to immunise against external vibrations. Not only that but this: “The top panel differs from earlier models because it consists of a sandwich of steel and 4mm of tempered glass, giving the Pavane her own distinct look”, says Rujtenberg.
Also unlike the Hex, both AES/EBU and USB inputs and balanced outputs come as standard.
The Pavane will be available in both silver and black and ships with matching aluminium remote control for source selection.
Pricing will ultimately land at €4095 (+ VAT) but an introductory price of €3695 (+ VAT) will hold until the end of January 2015.
Further information: Metrum Acoustics