To play the Anton Ego gold card of Ratatouille—the aged reviewer with the huge attitude whom nothing pleases—let's handle the nits first; all two of 'em. First, the 'trim pot' to determine mode of operation (stereo, mono biamp, mono bridge) isn't marked. It's just a slotted cross with no indication of where it's been set. Obviously the factory default is 1=stereo upon delivery. But since proper speaker hookup depends on the chosen mode, a visual identifier on whether the amp has been bridged would be useful. Actually, a small 3-pole toggle would be more convenient altogether. Which gets us to #2. There's no silkscreen on how to connect speakers in mono mode. It's explained in the owner's manual of course. And the rear panel does identify the left 10KΩ RCA or 20KΩ XLR as the mono inputs selected by toggle. It simply remains mum on how to use the banana sockets. That's peculiar. As you can see, there's plenty of blank space for the necessary writing. As it turns out, mono uses only the red banana sockets. Now the left becomes plus, the right minus. Hey, I did invoke Anton Ego's crotchety curmudgeonly self for a reason. Anyone else would shrug off these items as being super fussy. The average end user will either leave things in stereo as delivered; or consult the manual for doing the mano-i-mono thing just once and be done.

And even this writer is done now to move from nits to nuts. The mb55 wouldn't be a Lindemann without invisible smarts. Here that's intelligent power management. Powering up immediately triggers 1-watt readiness mode. That's kicked into 800W-peak action (25-50W average) with a signal-sensing circuit. 30 minutes of inactivity revert back to 1-watt readiness. 30 minutes of that without signal invoke standby. Now power draw is down to a measly but Brussels-approved 0.5 watts. About the UCD module, the manual cites "fully discrete circuitry" for which "careful fine-tuning released the full potential of this technology". Its 24.5 x amplification factor nets 27.8dB of voltage gain with a claimed <0.05& THD+N. More smarts from the switch-mode power supply give us happy-happy AC smiles between 90 and 264V @ 50/60Hz. That means great tolerance for significant over/under voltages, no smoke or shut-down involved. Finally operational temps will be about 20°C under normal conditions.
Heliox 2x250w half-bridge class D power module and matching PSU HD200 switch-mode power supply.

Should the amp's comprehensive protection circuitry be triggered, a second pin-prick LED in red will light up next to the yellow power indicator which is the sole detail on the plexi faceplate.

Bridging the pair of mb55 right off to run some break-in on my desktop proved perfectly uneventful. As soon as first 1411mbps Qobuz Hifi then 320mbps Spotify+ streamed some tunes, the circuitry kicked into gear and made sound. The only thing unexpected were the slowly blinking power LEDs. I'd expected them to stay solid. Since this behaviour wasn't accompanied by volume cycling up and down, I quickly forgot about it.

The obligatory kitchen-counter photos show two solid aluminium bars to which mount various transistors. Part of the Heliox PSU board is concealed beneath a thin plastic sheet. The smaller PCB next to it is the output power board. In front of that sits Lindemann's input board.

The mb55 is another example of modern circuit miniaturization. A traditional mono amp of matching power with a linear power supply would be significantly larger and heavier. How that reflects in measured performance is shown next.

Once the amps had clocked the obligatory 100 hours on my desktop, circumstance delivered a pair of Kaiser Acoustics Kawero! Classic speakers for review. Their fully grown dimensions and 4-driver 3-way array of top transducers made for a perfect high-power op. The mb55 thus migrated straight into the big system before concluding this tale on the desktop as shown.