The best of all worlds – amplified
MBL’s Linear Analogue Switching Amplifier (LASA) is a proprietary circuit technology that brings together what belongs together, the most sought-after features from different amplifier concepts.
In an ideal world, every amplifier would be a device of simple function and pure character. Like a magnifying glass, it would simply enlarge music signals without omitting, adding, coloring or bending even the most delicate of sounds. And its power supply would be put to use for the benefit of the music alone – not to warm up the listening room with excess heat.
The world, however, is not ideal. Some amplifiers seem to produce more heat than power, but are capable of enchanting their listeners with rich, studio-quality sound. Other amps deliver a full performance and stay cool, but may sound frosty, rather than sunny; brittle rather than welcoming.
So, does amplifier technology really have to compensate for every advantage with a corresponding trade-off? Not at MBL, where our developers’ answer to this question is the Linear Analogue Switching Amplifier – better known as LASA. This ground-breaking amplifier concept combines high-energy efficiency with a sound quality that is simply captivating. MBL introduced LASA technology in 2011 with the debut of its Corona Line of amplifiers. Several years later, LASA 2.0 was presented to the world in MBL‘s Noble Line family of amplifiers.
Amplifier technology – a class system
The audio world defines the circuitry principles of conventional amplifiers by letters of the alphabet, with different letters representing distinct properties.
For example, a specific skewing of the music signal, commonly known as artificial harmonics or distortion, is an unwanted addition to the music. Class A amplifiers do not produce any such crossover distortions; they deliver homogeneous distortion characteristics, consistently low across all frequencies of the music signal, even at different volumes. Their function is also largely independent of the electrical properties of the connected loudspeakers. This behaviour has a great effect on the sound, but comes at a cost. Class A amplifiers draw substantial amounts of power and convert a significant portion of it into heat. As such, they require large heat sinks to dissipate this wasted energy, along with plenty of ventilation space on all sides so that ambient air can freely circulate.
Class AB amplifiers work in Class A mode only when the volume levels are low. When the sound level is turned up they switch to the more efficient Class B operation, which uses electrical power more efficiently and produces less heat. Their consistent amplification at all pitches – technically speaking, their linear frequency response – does not change with the properties of the connected speakers. The drawback to this amplifier class is instances of crossover distortion, where the distortion changes depending on the frequency and power. Audio experts’ rule of thumb is that Class AB amplifiers tend towards non-linear distortion, but depending on the volume intensity, this can disrupt one’s musical enjoyment.
Class D amplifiers, also known as “switching amplifiers,” are even more efficient. Not even five-alarm party volumes can get them hot. Their compact housing remains, at most, warm to the touch, but their distortions can vary with the pitch of the music, and their harmonic distortion factor is non-linear. They’re also designed to work with the specific resistance value of the connected speakers in mind – a value of 4 ohms for example. But the AC resistance (impedance) of loudspeakers varies with the frequency of the music. In the case of Class D amplifiers, this can lead to fluctuations in the frequency response, and overtones in the treble range.
The challenge? Is it possible to combine the musical beauty of the Class A amplifier with the stability of the Class AB group and the enormous practical benefits of Class D amps? The answer is a definitive “YES,” and MBL has found it with LASA. LASA amplifiers harness various independent technologies to produce music with a lightness that allows emotional connections. Catchwords like "confident" or "relaxed" are often used to describe the LASA effect in listening test reports. Why is this?
The laboratory litmus test - overcoming complex loads
Conventional measurements and standards fail to explain the complex ingenuity behind LASA technology’s capabilities. According to accepted laboratory audio standards, when an amplifier runs at maximum capacity, there’s a measured resistance between the audio system‘s loudspeaker terminals – typically with resistance values of 4 ohms or 8 ohms. But in the real world outside of the lab, the amplifier has to deal with loudspeakers which perform nothing like a well-behaved measuring resistor. The coils and capacitors in the crossovers, and the loudspeaker chassis itself, not only alter the resistance depending on the frequency, but they also react in a lively and unpredictable manner to the phase position (the temporal relationship between current and voltage). Taken together, those complex electrical “interactions” can decisively fluster a power amplifier.
Through the development and integration of its own proprietary measurement scheme, MBL’s LASA technology precisely simulates complex loudspeaker loads in all possible situations, including the mythical four-quadrant test (4QT). The 4QT measurement diagrams show that LASA amplifiers are able to effortlessly drive loudspeakers with many different electrical properties. With LASA 2.0, the latest development of this successful concept, MBL has further optimized its technology in order to provide musical playback that is always stable, powerful, and brilliantly transparent.
Technical properties of LASA amplifiers
- High-efficiency, low-heat radiation.
- Low, frequency-independent distortion; no adverse changes take place in the tonal characteristics of different instruments or voices.
- Load-independent frequency response; the frequency response is stable with different loudspeakers.
- Frequency-independent and uniformly high damping factor, which allows orderly control of the loudspeakers in all frequency ranges, and leads to well-articulated bass registers.
- The ability to effortlessly drive complex loads (loudspeakers).
- Soft Clipping: even at very high volumes or difficult loads, the amplifier treads very carefully into the overload range without sounding aggressive or distorted, unlike Class AB and Class D amplifiers whose circuitry leads to hard clipping.
- Rectifier with low transfer losses.
- Intelligent ground routing with effective common-mode rejection; particularly beneficial when interacting with other audio devices.
LASA 2.0 amplifiers – the next level
- Further improvement of the 4QT capacity (full control in all phase positions).
- Differential amplifier inputs for better common-mode rejection, i.e. no negative mutual influence between the amplifier, pre-amplifier, and source components.
- Introduction of a low-impedance grounding concept for the supply voltage and the output stage, thereby increasing the transparency with greater control of the frequency response.
- Enhanced ability to drive complex loudspeaker loads.