Specifications:
https://www.mola-mola.nl/Maku.html
https://www.mola-mola.nl/DAC.html
Some tech from the designer Bruno Putzeys explaining to me some of the aspects of the dac design:
The upsampler and modulator are written in software. The upsampler is an asynchronous sample rate converter. You can also buy chips that do that but they only come with "just good enough" filter responses and neither do they have a particularly narrow PLL bandwidth so there was no alternative left but build one from the ground up. The choice for asynchronous vs using multiple clock crystals was made because you can't make a tuneable oscillator with the extremely stable SC cut crystal that MM use.
Far from being hard coded, the entire thing is completely software defined. OTOH the user has no say in what type of filter it uses, it being felt that allowing users to toy with it was a gimmick, since for every input rate there can only be one filter setting that is least audible (the filters change with input rate and format). It follows that any one might add just for the sake of "giving users a choice" would be more audible.
The modulator is PWM and is based on a scheme invented in 2004 to generate noise shaped PWM. It should be noted that it's not an n-bit noise shaper followed by a conversion to PWM but the PWM is noise shaped directly. Of course, from an information perspective we're still looking at the equivalent of 5 bits at 3.125 MHz however you want to look at it. The gory details are in https://www.hypex.nl/img/upload/doc/an_wp/WP_AES120BP_Simple_ultralow_distortion_digital_PWM.pdf
What sets this type of PWM aside from ordinary 1-bit sigmadelta is that it is inherently free from intersymbol interference. If you reproduce a 1-bit signal using a switching circuit whose rising and falling edges aren't exactly symmetrical you get a distortion component equal to the number of 1/0 transitions per second, which varies with the signal and which has tone like components. With the single-edged PWM conversion the number of transitions per second is constant and only one of the two edges encodes a signal so the same rising/falling asymmetry would cause nothing worse than a tiny amount of DC offset. This observation was first made by Peter Craven in 1993, who was then trying to design a DAC for B&W and published a way of generating such a signal. So if you are looking for a historical precedent for using PWM in a DAC, that is the closest you'll get. If you compare Craven's paper (http://www.aes.org/e-lib/browse.cfm?elib=7001 ) with the one linked above you can see the new method is significantly more straightforward and has lower distortion.
The FIR trick is this: if you generate a clocked PWM signal with a period of N clock cycles, and you run that through a FIR filter with N equal valued coefficients, the output of that FIR filter is simply the total number of ones over the past full cycle. This removes the PWM switching frequency and some shaped noise from the output signal, making life easier on the analogue filter that follows. The resistors need not be matched since each tap sees the complete signal. A mismatch only slightly affects the attenuation of the 3.125MHz component. This is why FIR DACs are used. They have been around in some form or other since the mid 90's. I'm not sure about other commercially available PWM based FIR DACs though.
Quotes from two recent reviews (not available as links at this time)
Hi-Fi Choice:
Makua Pre/DAC: " Like: Spacious, open sound, build, excellent app control. Dislike: Nothing. We say: Super versatile and capable modern preamp.
Hi-Fi News:
"....its aforementioned unflappability at high volumes and smoothness from bottom to top- it''s another facet that's part of its big, confident yet calm character."
"Bass was lithe and tuneful, the mid band delicate and satisfyingly three-dimensional, while treble has a wonderful satiny texture to it."
Test set up:
AQVOX switch with King Rex dc ps in port 1 out port 8 and grounding wire , AQVOX and Vovox Ethernet cables, fidata network work server, Vovox USB to dac, Lumin S1 using digital out, Mola Mola Makua preamp with dac module, Mola Mola Kaluga mono block amplifiers, Hi Diamond XLR 3 interconnects, Boenicke W11 with external Bybee speaker bullets, Hi Diamond 7 speakers cables, separate mains spurs to each component terminated in IEC plugs and dedicated consumer unit, Bybee signal enhancers under each individual component including the hub and switch, SteinMusic Harmonizers with blue suns and diamonds, Bybee signal enhancers in the room at various points, room 3.5m. x. 7m x 2.5m.
Comparisons: Chord DAVE, Lumin S1 built in dac, Benchmark DAC2, SST with dac module.
TBC
