The idea of a highly efficient amplifier with high electrical output, low power consumption and reduced heat generation has always been very attractive indeed.

Bruno Putzeys from Netherlands has been deeply intrigued by this design approach for many years and should be given the credit for some big advancements in this field.

A class-D amplifier or switching amplifier is an amplifier in which the amplifying devices (transistors) operate as electronic switches, instead of as linear gain devices as in other amplifiers. The signal is a train of constant amplitude pulses, so the active devices switch rapidly back and forth between a fully conductive and non-conductive state. The analog signal is converted to a series of pulses by pulse width modulation, pulse density modulation or other method before being applied to the amplifier. The dynamic range and signal-to-noise ratio of the Class-D amplifier are controlled by the switching frequency. The switching frequency must be very high to achieve the necessary resolution. However, the drawback of increasing the switching frequency is that the amplifier will be less efficient. After amplification, the output pulse train can be converted back to an analog signal by passing through a passive low pass filter consisting of inductors and capacitors.The largest advantage is in efficiency. Improved efficiency translates into lower system cost, lower operating temperatures, lower power supply voltages, and lower power consumption. 

Class-D amps can use switching mode power supplies as well as linear ones but majority of them use the former.

There have been numerous attempts to introduce this technology into the high end audio sector but in some other market segments it already appears to be fully established like for instance in the car audio segment, small portable devices (mobile phones), computer active speakers and even in public address systems.

Meet the MAKUA and KALUGA

The Makua preamp and the Kaluga monoblock power amps all share the same, stunning design traits. The visual aesthetics and fit and finish are simply first class, hands down. The extremely elegant curvature on the front and top are refreshingly different from the usual square, shoe box styling.

From their website we read that:

“Mola-Mola embodies the idea that once you've removed everything that isn't the music, what remains is the music.

This is radical. Today's high-end audio has become all about mixing circuit topologies and parts to make a sonic blend that the designer thinks “sounds about right”.  You'd almost forget that getting closer to the sound as crafted by the artist really means keeping the replay system from changing it.

Turning this simple insight into hardware is probably the toughest way to do audio. All simple circuits change the signal audibly, so one has to get to grips with more complicated ones that don't. I analyse every sub-circuit mathematically and look for ways to eliminate every error term. When the practical circuit measures as predicted, I listen to search for unexpected sources of colouration. These are then included into the maths and the whole process repeats. 

After every stage has proven immaculate performance, the same is done with the whole product and so problem spots get methodically rooted out before they hide themselves and become “audible but not measurable”.

The result is something never before heard of in high end audio: amplifiers and converters whose output signal cannot be distinguished, by ear, from the input signal. So what does that sound like? In a few words: natural, nimble, rich and musically enthralling.”

Not everything from the above sounds logical and some of it runs contrary to the prevailing and proved wisdom: “All simple circuits change the signal audibly, so one has to get to grips with more complicated ones that don’t. Isn`t it the other way around?

Next: “When the practical circuit measures as predicted, I listen to search for unexpected sources of colouration. These are then included into the maths and the whole process repeats.“ I do wonder how can “colouration” which is a subjective term, be included into math which is objective, exact (not approximated in any way) by definition?

“I am sure there must be some hidden meaning in the above although at the moment I fail to recognise it - perhaps the listening tests and the manufacturer`s comment will reveal the obvious?”

The MAKUA preamp

The MAKUA preamp seems extremely well equipped and designed, especially the option to integrate a DAC, a phone stage and the optional tone controls is a big bonus:

“With the knowledge in hand to design minimally invasive electronics without needing to be minimalist, we decided that our preamp should be complete. Very complete.

The basic Makua is an extremely transparent gain stage and a programmable routing matrix. The chassis has ample room to fit optional extras, most notably a DAC and a phono stage. The 6 preset buttons are programmable via USB or Bluetooth to access any combination of channel, processing and routing. In a system with mainly digital sources, the preset buttons would be programmed to select between them. Vinyl lovers on the other hand might want to use several buttons to select the same turntable but with different EQ settings to suit their large collection of historic LP’s. All five inputs are switchable between XLR and floating RCA connections, and all can be assigned as either phono or line.

All stages in the Makua use discrete amplifier modules in a little known topology called “single-ended driven differential”. Compared to doubly executed signal paths, this structure prevents noise from propagating all the way through. The Makua is amazingly immune to influences like mains quality and choice of interlinks. The relay-based volume control directly controls the gain of the output stage. Dynamic range and linearity of this arrangement is much greater than those of stepped attenuators. Operation is smooth and entirely glitch free.” 

Inputs and outputs:

5 balanced and 5 unbalanced inputs, all routable through optional processor boards like the phono stage.
2 parallel outputs for bi-amping.
4 programmable trigger outputs.


Balance and input gain offset.
Phase invert and mono sum.
Optional tone control.
Full software control of routing and processing


Maximum input/output level: 20 dBu (7.75 Vrms)
Unweighted noise voltage at unity gain: 1.9 uV
Input impedance: 100 ohm
Output impedance: 44 ohm
Distortion at maximum signal level (THD, IMD): not measurable, estimated around -150dB.
Bandwidth >200 kHz
Gain range: -70 dB to +15 dB.
Gain resolution: <1 0.2="" better="" db="" i="" listening="" normal="" over="" range.="" than="">

Dimensions and Weight:

420mm(W) x 110mm (H) x 345mm (D). Depth includes volume knob and connectors.

The KALUGA mono block power amps

Housed in a relatively small enclosure, the KALUGA mono blocks are packed with high tech solutions:

“Kluge is based on world’s most sought after class D technology: Ncore. Also designed by Bruno Putzeys, this circuit packs 20 years of research and experience into non-linear control theory.  Unprecedentedly low distortion, noise and output impedance combine into what scores of enthusiastic users unanimously describe as “no sonic signature at all”. 

Just music, glorious music. For instance, the two supposedly unassailable strongholds of class A amplifiers are linearity and output impedance, at high frequencies. Plotted below are the output impedance as a function of frequency and the output spectrum in a high power (400W), high frequency IMD test. In both cases Kaluga outperforms any power amplifier, regardless of technology, operating class or asking price, of which such test results are available.

The amplifier board is a Mola-Mola-specific design deriving from the famous NC1200 amplifier. The audio circuitry is trimmed to the bare bones and board-to-board connectors are eliminated in favour of soldering a pair of star-quad cables directly into the circuit board for the cleanest, lowest impedance connection possible. The input stage is moved to a separate circuit board that uses the same discrete buffers as those found in the Makua. The redesigned output filter sports monolithic capacitors whose dielectric stability is reflected in an impressively neutral and poised rendition.

The days of compromising power efficiency for audio performance are finally over: the Kaluga delivers definitive audio performance with power efficiency thrown in as a bonus. 


Output power: 400 W/8 ohm
700W/4 ohm
1200W/2 ohm
Gain: 28 dB
Unweighted Signal/Noise Ratio: 128 dB
Distortion (THD, IMD): <0 .003="" all="" and="" br="" frequencies="" levels="" power="">Input Impedance: 100 ohm
Output Impedance: <0 .002="" ohm="">4000), all frequencies.
Bandwidth: >50 kHz

Inputs and outputs

Balanced and unbalanced input.
2 pairs of Furutech binding posts, bewared directly to the amplifier PCB using Kubala·Sosna cable.”

A different approach

Throughout the world the “class-D” sound was accepted with mixed reactions; some praise it, some hate it. Renowned authors like Martin Colloms, Michael Fremer and Lynn Olson do not seem to be convinced by this technology. Personally, up to this point all the class D amps that I have heard, ranging from the old Spectrons, ICE modules equipped amps, Hypex UcD module equipped amps, NuForce amps, Devialet, etc, all seemed to offer a somewhat familiar sonic view. I am not saying they sounded exactly the same, but they did sound very similar. These amps sound radically different from the analog solid state and tube amps - in almost every regard. An experienced listener who happens to be an avid concert goer will most likely have a hard time finding parallels with the live sound - the sound of un-amplified acoustic instruments and voices. The main ingredient that seems to be missing is that “life sparkle” one experiences live (micro dynamics). The music just lacks the energy of live performances and here, the analog amplification is still unbeatable. Perhaps the most organic and natural sounding class-D amps were the hybrid ones, which used the tubes in the driving stages. Of course, many class-D amps are really powerful… on paper, but somehow they fail to breath the life into musical performances. 

I am not sure whether this is the result of badly implemented SMPS or anything else. 

I must admit I have really warmed up for the idea of a small, cool amplifier that is potentially able to replace all those big, heavy and hot analog amps and show them a lesson or two. Throughout the years I have kept an open minded attitude towards class-D amps. I thought it is only a matter of time when a real game changer will appear and smash the old fashioned analog competition. Every time I would stumble upon an enthusiastic class-D amplifier review, I would say to myself: it is here! Unfortunately, when I have heard them for myself, I was deeply disappointed; none of them delivered what the reviews promised. But, I keep waiting... 

The sound of MOLA MOLA

In use I have found the MOLA MOLA Makua and the Kaluga to perform flawlessly; everything worked smoothly and the amps performed reliably. 

The MOLA MOLA trio was already burned-in when I got them. The Ncore technology supposedly represents a giant step forward in the field of class-D amplification and my expectations were set pretty high but…

The combination was certainly able to produce high sound pressure levels, make no mistake. The frequency range they reproduced was wide and reasonably uniform.
Starting with the bass, it was quite extended but I have missed some control across the entire bass range and especially in the upper bass/kick drum area where the Kalugas sounded somewhat lean and anaemic..

The familiar music didn`t sound much familiar through the MOLA MOLAs; in the midrange the voices did not posses enough dose of “human touch” to sound real.

All notes were there but the illusion of musicians standing in front of me wasn`t convincing at all. The music didn`t sound inviting and involving, it was just… there.

The emotional content was missing and the tonal colours were somewhat bleached.

For lovers of analog reproduction and concert goers the sound could also be quite fatiguing and plain boring.

A quick comparison with the Crayon CFA-1.2 showed that this little class AB integrated (with a SMPS) reproduces music that is packed with energy and sparkle - it was unbelievable! It even managed to sound more powerful within a certain power envelope. The Crayon amp sounded much more reminiscent of the real thing, even the bass was punchier and more controlled at the same time.  

For a brief period of time I have tried the MAKUA preamp with two power amps I have had on hand. Surprisingly, only positives could be reported here. This preamp offers performance worthy of pairing with the best analog power amps. In all parameters that matter the most, like the energy transfer, micro and macro dynamics, resolution, transparency, 3^D holographic image precision, soundstage air and reverberation cues, bass slam and extension, etc - it just leaves one amazing impression.

If with the KALUGAs the sound was far from involving and believable, the MAKUA driving the analog amp - it was completely a different story. The emotional content was fully delivered and ensured a very high involvement factor.

I really regret the DAC and phono modules were`t fitted because something tells me that MAKUA preamp could be a giant killer in one small package.


A big thumbs up for the MAKUA preamp! In its completely equipped form this preamp could represent a central controlling unit of the highest quality degree. It is very cleverly designed, potentially packed with features and offering a stellar sound in every imaginable regard. The visual aesthetics are stunning and the level of finish is extraordinary. It warrants my highest recommendation for anyone looking for something really special in this price class.

As for the KALUGA monos…in my view the time has not yet come. Perhaps many people will find them good in what they do and will happily live with them for many years, but it should be pointed that class-D amps offer a very different sonic perspective from what one hears live OR with good analog amplification, be it tube or solid state - regardless of the amp`s working class. If the sound of KALUGAs would be declared as very lifelike, then I fear we would be sending a wrong message to the audio amplifier industry, not to mention deny the reality. There is just no way one could consider both, the analog and switching amps equally capable of materialising that grand illusion of performers playing and singing in front of us - this is just impossible due to huge differences in sound. 

I still hope this class of amplifier operation will some day reach a mature status and will deliver what it has promised for decades. Until then…

Mola Mola

Kattegat 8
9723 JP Groningen
The Netherlands

+31 50 526 4993

PRICE: KALUGA (per pair) 12.000 EUR, MAKUA 10.000 EUR (basic model)