Reviewer: Srajan Ebaen
Financial interests: click here
Sources: Retina 5K 27" iMac (4GHz quad-core with Turbo boost, 32GB RAM, 3TB FusionDrive, OSX Yosemite, iTunes 12.2), PureMusic 2.04, Audirvana 2, Qobuz Hifi, Tidal Hifi, COS Engineering D1, Metrum Hex, AURALiC Vega, Aqua Hifi La Scala MkII, SOtM dX-USB HD w. super-clock upgrade & mBPS-d2s, Apple iPod Classic 160GB (AIFF), Astell& Kern AK100 modified by Red Wine Audio, Cambridge Audio iD100, Pro-Ject Dock Box S Digital, Pure i20, Fore Audio DAISy 1 [on review], S.A. Lab Lilt [on review], Metrum Acoustics Pavane [on review], Lindemann Audio music:book 15 [on review]
Preamplifier: Nagra Jazz, Esoteric C-03, Bent Audio Tap-X, COS Engineering D1
Power & integrated amplifiers: Pass Labs XA30.8; FirstWatt SIT1, F6; Crayon Audio CFA-1.2; Goldmund Job 225; Gato Audio DIA-250; Aura Note Premier; Wyred4Sound mINT; AURALiC Merak [on loan]; Lindemann Audio music:book 55 x 2 [on review], Goldmund Telos 360 [on review]
Loudspeakers: Albedo Audio Aptica; EnigmAcoustics Mythology 1; soundkaos Wave 40; Boenicke Audio W5se; Zu Audio Submission; German Physiks HRS-120, Gallo Strada II w. TR-3D subwoofer; Crystal Cable Minissimo [on review]; soundkaos SK16 [on review]
Cables: Complete loom of Zu Event; KingRex uArt, Zu and LightHarmonic LightSpeed double-header USB cables; Tombo Trøn S/PDIF; van den Hul AES/EBU; AudioQuest Diamond glass-fibre Toslink; Arkana Research XLR/RCA and speaker cables [on loan]; Sablon Audio Petit Corona power cords [on loan]
Power delivery: Vibex Granada/Alhambra on all components, 5m cords to amp/s + sub]
Equipment rack: Artesania Audio Exoteryc double-wide 3-tier with optional glass shelves, Exoteryc Krion and glass amp stands [on loan]
Sundry accessories: Acoustic System resonators
Room: Irregularly shaped 9.5 x 10m open floor plan with additional 2nd-floor loft; wood-paneled sloping ceiling; parquet flooring; lots of non-parallel surfaces (pictorial tour here)
Review component retail in Europe: €2'800

As marketing director Christopher von Delhaes put it, " the Lindemann musicbook:50 power amp is a sonically excellent mate for our network players and USB DACs. But we are aware of its 80wpc power limit which has occasionally caused it to shut down into self protection when used with certain low-impedance loudspeakers. Now we have a solution for such users with our new 'big' musicbook:55. Designed into the same trademark case work of our musicbook range, it now offers 240wpc into 4Ω or 450 watts into 8Ω bridged mono to drive any speaker. A switch on the rear configures the amp as either a stereo amp; for mono bi-amping; or for mono bridge mode." The musicbook:55 is based on latest-gen UCD tech which one might assume to mean the Dutch Hypex company and D-class expert Bruno Putzeys whose nCore amps have turned heads over the past year; yet as we'll see, the capital 'C' denotes a difference as the Hypex/Phillips trademark spells UcD. The upgrade in coin over the €1'800 model 50 is an even grand, hence €2'800. That gets you an attractively Scandinavian-style petite stereo/mono power amp which packs an unexpected yet very green punch.

Norbert Lindemann at the Swiss HighEnd 2014 with a prototype musicbook:55 powering Manger speakers.

This review is part II of my coverage on the musicbook:15 USB DAC, CD player, preamp and headfi amp (quite the mouthful for a small component). Since this range of German smartfi is modular of sorts by consisting of identically styled and sized components for targeted mix'n'match, it only made sense to cover how the 15+55 would add up. Needless to say, that wouldn't eliminate solo outings with competing gear. Here the source deck had already made quite an impression. To get started today, let's check out how the 55 handled itself on my desktop where it displaced Goldmund's Job 225 driving my customary Boenicke Audio W5se with an April Music Eximus DP1 front end.

If the headlines are anything to go by, class D has come of age. There's Raidho Acoustics' Aavik U-300 integrated. It's a whopping €30'000 with DAC and phono stage. There are the even whoppier input-transformer coupled Jeff Rowland Design Group €38'500 Model 825 stereo and equivalent 925 mono amps based on nCore tech. There's the $12'000 Theta Digital Prometheus mono, another nCore amplifier; and the up to 8-channel stablemate Dreadnaught IV. More n comes with Bel Canto's Black. Ditto the Veritas, Atsah and Kaluga monos from Merrill Audio, Acoustic Imagery and Mola-Mola. NAD and Tent Labs use the smaller nCore modules. Gato Audio promote Pascal. Mårten Design years ago built a massive pair of show demonstrator monos with linear power supplies based on what then was Abletec. Amphion use the newer Anaview boards for their pro amps. Roksan and AURALiC and MBL do it the UcD way from Hypex. April Music, Wyred4Sound, Bang & Olufsen and many others use ICEpower. Wadia and Boenicke do Italy's PowerSoft. SPEC do Texas Instruments. Audio Research roll their own D. So do Mark Levinson, NuForce, Classé and Anthem and Digital Amplifier Company. Ditto Devialet. Their proprietary paralleling of class D and A for current and voltage gain plays at the very forefront of new legitimacy for the breed. In short, the numbers of believers are rising, particularly so at the upper level. Class D for the high end used to be an oxymoron when it was considered fit only for subwoofer plate amps. Today switching analog output stages have infiltrated the upper end like body-swapping aliens ready to take over the planet. On price and size, Lindemann's big boys are dwarfed by Jeff Rowland and Theta Digital. Hence the musicbook:55 appeals to us of the less aspirated wallets; us of the thinner shelves; and even us of the daft desktoppers who try to get any serious work done whilst tunes come off seriously good kit. As the header promised, we'll power monger by trying both stereo and mono modes. Whilst the latter reads pure overkill for the desktop, my prior experiment with the Goldmund Job 250 monos said rather otherwise. It's not about 3dB more loudness for a doubling of output power; or even a doubling of SPL for 10 x the power. It's about better deeper soundstaging, more bass control, higher resolution and bigger tone.