The heart of Bruno’s Ncore circuitry
is, of course, feedback. Where UcD had a loop gain of 30.5 dB or x 34, the goal for Ncore was to exceed that substantially. To actually arrive at a class D circuit with 50-60dB loop gain wasn’t easy. Due to class D’s inherently limited bandwidth, there are limits also on how far unwanted harmonics can get pushed out of band. With an optimal 500kHz switching frequency, there’s less than half that bandwidth available to exploit the feedback trick. On the subject of high clock speeds, the switching nature of class D creates an effective antenna which liberally broadcasts RFI and EMI. To contain those effects, Mola Mola’s circuit is in compliance with the pro audio world’s AES48 standard which defines, for instance, the assignation of XLR pins. Pin 1 should never connect to ground which could cause hum. Pin 1 should only attach to the cable shield whilst the two other pins carry the differential signal. According to Bruno, audiophilia's empirical matching is borne out of sloppy circuit design, subsequent ground loops and undue sensitivity to EMI/RFI. Now only luck chances upon optimal system configurations because there’s a sad lack of standardization and manufacturers themselves don’t much help from the design of their PCBs on up.

Back to our review subject, we finally received a pair of Kaluga by mid 2015 to end our most protracted preview limbo ever. Bruno hand-delivered two Kaluga and a matching Makua preamp. When we opened the heavy-duty transport cases, the new finish stared at us clear as day. Where the pre-production samples we’d welcomed in the last quarter of 2013 had had a fine matte finish, final production was far more sophisticated. Its aluminium surface looked a bit like leather with a very fine pebble grain. At first we thought that the surface was like the skin of the actual mola mola sunfish or Kaluga sturgeon but this was actually more like very fine sand paper where the sturgeon would be more irregular. Most aluminium surface finishes are the result of abrasive belts. Mola Mola’s appears to have used a water jet and/or sand blasting. Either way, it looks great. To prevent finger prints, a pair of white cotton gloves is included.

Each Kaluga measures only 340x215x110mm but weighs 9kg. Where most designers go for a boxy case, the Belgian/Dutch team went for a wave-like form in accordance with their watery theme perhaps. From a viewer perspective, the Kaluga fascia is quite concave. In its middle sits a tiny shiny switch while at the very edge between concave fascia and onset of wave top sits a mini LED. A nice detail is that when in standby, the LED’s red glow is hardly visible in daylight whilst begging to be switched to the white light of the 'on' position at night. Riding on the wave is an etched Mola Mola logo. Three sides of the Kaluga casing are straight black aluminium panels with rounded edges nicely contrasting with the eye-catching wave of the front and top. At the business end are a set of analog inputs on XLR and RCA plus a switch between the connectors to make the selection. Under the RCA connector lives a trigger input to enable remote control of the power cycle.  Next are two pairs of top Furutech FP-803 binding posts. Those encourage bi-wiring and combined with the amplifier’s very low output impedance, this hookup approaches bi-amping on sonics. A ventilation slot above the speaker terminals communicates with openings in the bottom plate for some cooling airflow. A power IEC receptacle concludes the tour of the amp’s back.

For global use, Kaluga sports an auto-sensing power supply whose software runs an anti gray-market AC lock. Legitimate owners can have their power supply reset by a dealer when they move to a country with a different AC voltage rating (say from 230V to 115V). As mentioned before, with Kaluga the cookie crumbles rather differently than with our Ncore NC1200-based OEM demonstrators. [Here it’s instructive to note that amongst Ncore OEMs today already are Acoustic Imagery, Bel Canto Design/Bel Canto Black, Jeff Rowland, Merrill Audio, NAD and Theta Digital – Ed]. Bruno tricked out his own version very heavy on parts. For starters, the input stage became the same as that in the Makua preamp. Its development so satisfied him that a derivative version ended up in the Kaluga. Next to a highly linear very high input impedance to meet any source impedance head on, this input buffer also exhibits extremely low distortion. The net result of these improvements is an amplifier module different from the NC1200 board which thus remains exclusive to Mola Mola and won’t be available to OEM competitors.

Bruno's in-house hot-rodding includes the power supply. It operates with small currents because all rectification is handled on the primary side. This enabled smaller capacitors to still provide sufficient storage capacity whilst their reduced physical size made for a parts layout on the PCB that exhibits only minimal current loops. For its SMPS, Kaluga runs a 100kHz switching frequency to use a smaller transformer whose radiated field in turn was easier to shield. By addressing the 100kHz harmonics, this SMPS is said to be one of the quietest possible. As such, our original A/B comparison hadn't been fair. The Kaluga had grown into a different beast than our more basic tech demonstrators. Hence we opted to let the Kaluga loose on all our resident speakers, with a streaming input that was attenuated either in software (XXHighend), magnetically with our Music First transformer passive—on the floor in the above photo—or the matching Makua loaner when Qobuz or Tidal were sourced via our La Rosita.