Reviewer: Marja & Henk
Financial Interests: click here
Sources: PS Audio PWT; Dr. Feickert Blackbird MKII/DFA 1o5/Zu DL-103; Phasure XX-PC; SoundGalleries SGM [loaner]
DAC: Phasure NOS1 DAC; T+A DAC8 [loaner]
Streaming sources: XXHighEnd; iTunes; Devialet AIR; La Rosita Beta; Qobuz Desktop, Tidal Desktop
Preamp/integrated/power: Audio Note Meishu with WE 300B (or AVVT, JJ, KR Audio 300B output tubes); dual Devialet D-Premier; PTP Audio Blok 20; Hypex Ncore 1200 based monoblocks; Trafomatic Kaivalya; Trafomatic Reference One; Trafomatic Reference Phono One; Music First Passive Magnetic
Speakers: Avantgarde Acoustic Duo Omega; Arcadian Audio Pnoe; Podium Sound One; WLM Sub 12; Sounddeco Alpha F3; dual Zu Submission MKI; Soltanus Virtuoso ESL
Cables: complete loom of ASI LiveLine cables; full loom of Crystal Cable cables; full loom of Nanotec Golden Strada; Audiomica Pearl Consequence interconnect; Audiomica Pebble Consequence;
Power line conditioning: PS Audio Powerplant Premier; PS Audio Humbuster III; IsoTek Evo 3 Syncro; AudioMica Allbit Consequence
Equipment racks: Solid Tech and ASI amplifier and TT shelf
Indispensable accessories: Furutech DeMag; ClearAudio Double Matrix; Franc Audio Ceramic Disc Classic; Shakti Stones; Akiko Audio sticks; Kemp polarity checker
Online Music purveyors: qobuz.com, tidal.com, bandcamp.com, amazon.co.uk  
Room treatment: Acoustic System International resonators, sugar cubes, diffusers
Room size: ca. 14.50 x 7.50m with a ceiling height of 3.50m, brick walls, wooden flooring upstairs, ca 7 x 5m with a ceiling height of 3.50m, brick walls and concrete floor downstairs
Price of review item:  €4'000 ex. VAT

Back in the (g)olden days of the first digital music recording and playback, there was just one flavour of encoding. It was pulse code modulation or PCM. Basically, PCM samples the incoming analog signal at regular intervals. Each sample has a certain value. However, these values do not necessarily match with, let's say one of the 65'535 values possible in 16-bit digital encoding. A sampled value can be a tad too high or a tad too low to match an exact preset value. To actually match the samples with a preset value, the sampled value is rounded off to the closest matching preset value. This is called quantization. It already will be clear that a higher bit rate offers more preset values, hence rounding errors have much less influence on the outcome which is much more in accordance to the input. Once the original analog signal is sampled and quantized, the resultant stream of ones and zeros can be stored. Mind you, this does not apply for audio CD storage. An audio CD contains no ones and zeros. Instead it contains a stream of lands and pits. Each land and pit can be of one of 9 different lengths. The transition from land to pit or pit to land represents a digital ‘1'. A ‘1' is always followed by zeros until the next transition, hence another ‘1'. In any case, when the digital sequence is to be converted back to an analog signal which after amplification can drive our speakers, there is need for a DAC.

The original way Sony and Philips first converted digital back to analog was with a ladder DAC, an array of resistors which when connected looked like a ladder. It was not easy for Philips to build such a ladder because it was hard to get accurate enough resistors. This resulted in the original TDA1541 DAC which was not very accurate. In hindsight though, it sounded much better than the next gen method, the Delta Sigma DAC. Due to its passive analog process without any sampling or other calculations, the concept of the ladder DAC is much more purist than the active processing of later methods. Another plus is the unlimited speed its resistors work at.

In a ladder DAC—we take a 16-bit example for clarity—each possible value out of the 65'535 that 16 bits can represent is handled by a dedicated resistor pair. If the input to the DAC is the digital equivalent of 12, it is taken care of by the corresponding resistor pair and the output of the ladder presents the analog voltage value of 12. It is amazing that all these resistors work in unison and at dazzling speeds. For 16-bit 44.1kHz inputs, the circuit does its magic 44-thousand time per second. Luckily there is another trick that can limit the total amount of resistors needed. This trick is called R-2R (or R/2R). Instead of needing a resistor pair for each possible digital value, it reduces the 16-bit number 2/16 or 65'535 pairs to 2x16 or 32 pairs per channel. Next, there is no need for all different resistor values. Two values are enough. With this R-2R concept, a ladder DAC chip no longer was such a big deal to design and manufacture. Philips' TDA1540 was soon joined by BurrBrown's iconic PCM1704. However, these chips were expensive to make. When better measuring (!) cheaper Delta Sigma chips hit the market, the production of R-2R chips ceased and chip-based ladder DACs became collector's items.