Reader Jez Anderson: "I've been ignorant of LinnenberG amplifiers until recently. I bought a pair of Spatial Audio M3 Turbo speakers which I like very much. To compliment them, I bought a pair of Bel Canto 600m monos. Those are good but subdue some treble energy which robs the speakers of a certain excitement. I spoke with Clayton Shaw of Spatial to learn whether he had particular success with any particular amplifier. He said he'd bought himself the LinnenberG Liszt, having been amazed by their sonic qualities." Jez wanted to know whether they'd address the issue he had with his American class D amps. I assured him they would. That's because owning a pair of equivalent nCore monos from UK brand Nord, I'd long ago done that test against our Allegro. For redundancy, I did so again with the Liszt. Up they went into our smaller upstairs system anchored by a pair of Accuton-based Albedo Audio Aptica 2-way towers. Here the usual front end is a Soundaware SD card reader with integral DAC. That feeds ex April Music boss Simon Lee's small Stello 100MkII separates. This system serves up regular Osho Nadabrahma meditation music. For its first half hour, New Age composer Deuter used an assortment of singing bowls, bells and whatever other related objects he could scrounge up from the shops along Poona's MG Road during the late 1970s. No drums, bass, synths or rhythmic time keepers, just irregularly struck oscillating metal bodies ringing out lazily - or prematurely damped. When played at the intended low levels, there are plenty of ultra-fine Platinum-tinged ghost sounds at the very edge of audibility. Those hover behind the louder warbling sounds like faraway fractal streaks, some iridescently clear, others dirty and corroded. They can be so faint that just a thought is louder to miss them.

Despite their spectacular S/N ratio, the highly damped nCore amps with their copious use of negative feedback clamp down prematurely on these faintest of HF decays. They also obscure certain upper harmonic occurrences altogether unless I increase overall SPL to have them resurface. Here the affordable €1'200 50wpc class A/B Mosfet Stello amp is demonstrably superior. By roughly the same distance, the Liszt monos exceeded the little Korean on the inverted ceramic tweeters. The explanation could be their exploded bandwidth with a resultant lack of phase shift in the audible range; and less extreme damping factor than the nCores. Though certain switch-mode amps do have very good treble for class D—Digital Amplifier Company's Maraschino comes to mind—amplifiers like the LinnenberG still flatly trounce them on treble purity and finessed decays. As paid-up owner of the Nords, I say so without class bias. On speakers like Mark & Daniel's Maximus II monitor for example, the nCores' many strengths utterly dominated to become first choice from amongst my then amp inventory when I reviewed those ambitious synthetic stone speakers from Shanghai. On less hardcore loads, already the Allegro monos draw even on general resolution, eclipse the nCore in the treble, produce more natural bass and, across the bandwidth, inject more moisture and elasticity to counter the Nords' drier more rigid personality.

Relative to low-impedance stability of the bridged Liszt, I asked Ivo Linnenberg about the H-bridge mention of their specs. "An H-bridge is an optical representation of the actual output schematic. The horizontal line represents the speaker load whereas the two vertical lines stand for the push-pull output stage with active elements (4 times) over and under the middle line. In this respect, the output of the Liszt could be seen as a standard bridge circuit, easily obtained when connecting the load to the two 'pluses' and feeding the two stereo channels with opposite phases. Increasing the power output is the usual reason for doing so. Ideally a factor of 4 is achieved. The motivation for a full bridge with the Liszt was different although the power increase was very welcome. I wanted to have a fully symmetric signal path starting from the XLR socket going right through to the output binding posts. Signal routing and perfect symmetry are optimized for task and not comparable with a stereo amplifier used in bridged mono mode. With the Allegro, the symmetry ends at the output stage. The Liszt is really fully symmetrical. Nevertheless, physics laws remain valid regardless of why one uses a bridge output configuration. A 2Ω load connected to the bridge looks like a 1Ω load for any of its two sides. Liszt is perfectly stable into such loads but not recommended as a standard application."

About his chosen transistors, "these lateral Mosfets used in our Allegro and Liszt (or Goldmund, Nagra, Bakoon etc.) sound incredibly fine because they are ridiculously fast and linear. Very low and particularly linear capacitance between drain, source and gate is the main reason for that. This unavoidable capacitance in any semiconductor is extremely voltage dependent with most if not all other Mosfets, introducing a lot of unwanted distortion especially in the high frequencies. But there is a drawback with these lateral Mosfets compared to vertical Mosfets or bipolars: they are not as low impedance as those, making it difficult to build a brute-force amplifier with these fine parts." Anyone not considering 200w/8Ω sufficiently brutish stopped reading two pages ago. The rest of us appreciate that under most listening conditions, we tend to consume 5 watts or less. "The quiescent bias current per branch is identical for the Allegro and Liszt. The result is class A operation up to 3.5w/8Ω for both. Because Liszt uses two branches, one for each leg of the bridge, its total power dissipation doubles." A 90dB speaker listened to at medium volumes in a smaller room would thus run the Liszt in mostly or exclusively class A depending on recorded dynamic range. At the meditation ambiance levels of my secondary room, even our short 85dB transmission-line speakers would never depart this class A envelope.

We already learnt that Spatial's open-baffle speakers really get on with these silvery Germans. Jez's model runs two 15-inch woofers per side, one with a compression tweeter in its throat. Impedance is 4/3Ω nominal/min. Lacking the extra restorative force of air trapped inside a box, the back stroke of a dipole woofer only sees the room's air. Such loading benefits from excellent amp control. Clayton Shaw's choice of Liszt suggested that Ivo's high-speed circuit had the necessary braking power not unlike German performance cars. Those thrive on 180km/h where the Autobahn remains without speed limit but also flaunt absolutely massive brake calipers for all the obvious reasons. From Zu show demos, we've seen that the Liszt make an excellent companion for the 98dB Druid VI. This tracks with the very good results our Allegro make in-house on our Druid V. Even Rethm's Jacob George admitted that the LinnenberG were the best transistor amps he's heard yet even though he still prefers tubes. As it had with Jez then, word on Ivo and his kit was making the rounds with high-efficiency and low-impedance open-baffle speaker makers alike. Time to round up the usual subjects in the main system and A/B against the 55-watt stable mates.