We believe the Kassandra DAC is currently one of the best audio sources available today and can only be matched by top analogue sources in timbre and musicality, but keeping well ahead in aspects of dynamic presentation and resolution.

While in the process of setting up and building the company, at the earliest stages, the need of a true SOTA source was mandatory. You cannot claim to build speakers that aim to be the absolute best, top amplifier designs and so on, if you do not have a true reference source. And I mean reference in the true context.

My aim was making a true analog source, which would take Ones and Zeros as input, and I feel we succeeded.

Stavros Danos
DESIGNER: ARIES CERAT

The Kassandra Signature goes further than the Reference model and is built as a dual chassis design. The digital circuits and gain stage is housed in one chassis, the power supply in the other. This allowed us the enlarge the power supply and also use tube regulation. Even though the Reference model is huge for a one box DAC, we simply needed even more space for the Signature version.

The power supply is both tube regulated and filtered and uses xenon gas tubes. 

The digital board is also upgraded from 16 x AD1865N-K chips to 20 which further improves low level linearity. Total weight for both chassis is up from 60 kilos for the Reference model to 80 kilos for the Signature.

The source must be absolutely perfect

We developed the Kassandra as we felt no source on the market would stand up to the task. There would always be a certain character, lack of dynamics, lack of musicality and true analogue like timbre and flow. And these shortcomings would project onto our efforts to create the best speaker and amplifier combination possible.

In the audio industry today there is a race to find the best converter. As a result the market is saturated with digital processors and a new DAC is presented every week. It’s a race of numbers, with THD of -90db, oversampling at radio frequencies and 140db dynamic range. Yet many audiophiles change DACs as soon as the next one arrives, without ever finding the one that sounds “just” right.

In the process of developing our own reference system, we were also searching for the best available converter. Yet no converter delivered the sound that we expected. Every DAC presented an artificial feel to every recording, and almost all presented a compression of dynamics and poor flow of music, easily noticeable with uncompressed recordings and ultra high sensitivity horn systems. So we began designing the best possible digital processor. 

Delta sigma DACs are today’s standard for digital processors. Not because they provide better audio quality, but because of availability and ease of implementation of digital filters. Filters that became more and more complex, only because of the artifacts created with delta sigma modulation. The Kassandra’s prototype was developed very early, not as a commercially available design, but as a cost no object lab tool, my personal reference tool for speaker and amplifier development. The decision to put it in production and to be commercially available was decided at a much later stage.

We found since then, with many new converters launched daily with impressive specs. on paper, that they fell short of what we call analogue sound. They always presented that electronic signature that gives digital reproduction a bad name. The ladder DAC (R2R) is a resistor network switched by an N number of switches, N being the bit depth. It is a passive sort of speak procedure, whereas delta sigma (DS) technology, while still developing and moving forward, is a completely different kind of conversion procedure.

Creating an analogue signal from noise shaping (as in DS conversion) sounds counter intuitive. The very complex, very high order filters implemented to reconstruct the analog signal do create very good specifications on paper. However the high complexity of the filters and resultant very high energy (several KHz-MHz noise present) is what gives all DS converters their distinctive sonic signature, a sonic attribute often given the term ‘digital sound’.

Back to R2R principles, the individual resistors must be laser trimmed to an incredible accuracy, while making extremely high accuracy measurements. We chose to use an R2R IC, in our case the classic Analogue Devices AD1865N-K – a highly praised chip which we believe is the best sounding IC ever made. Many DACs use an IC converter in the usual “data sheet application” circuit, just adding their analog stage and, voila. We choose to design a converter that uses a number of IC R2R converters as components to a completely new converter system.

The AD1865N-K has a very straight forward data handling logic, and does not process the data stream in any way. This gave us the freedom to fully exploit the IC on our converter system. And our Super Clock circuit directly re-clocks and drives the “refresh” signal, so absolutely no additional jitter is induced in the conversion. This is not possible by any other IC converter.

These massive banks of the IC converters act as parallel switched resistor ladder converters, thus cancelling the deviation of the actual resistor values vs the theoretical. If the deviation of the resistor value from ideal is Gaussian, as the number of parallel resistor networks increases, the deviation from ideal is driven to Zero.

Jitter
We use many techniques regarding lowering and cancelling jitter, in both passive and active ways.

We solve this by using special driving circuits and carefully tuned digital line terminations for all our digital signals. Crosstalk between digital lines, ground noise and power supply noise can be a major source of jitter. Thus our DAC has extensive use of 35 LC filters implemented using RF chokes and high speed capacitors to decouple all digital circuits and ICs etc from the power rails. These are extremely effective in cancelling out any form of PSU sourced jitter. Jitter originating in USB and S/PDIF / Toslink sources are also eliminated right at the conversion enable line, or the ”refresh” signal of the converters.

A super clock is also used upstream for re-clocking the XMOS asynchronous USB controller, as well as the S/PDIF receiver. With the internal clock there is no need for a word clock input.

I/V
The R2R ICs are current output devices. Their impedance is very high and close to an ideal current source.To drive the next stage the current must be converted to voltage. Most converters use Op-amp circuits. We use a specially designed transformer that converts the current differential to a single ended voltage output. Many argue that the best current to voltage converter is an inductive element, and we are amongst those people.

Analogue stage
The analogue stage is a small single ended tube amplifier. It consists of a transformer loaded tube, driven directly by the I/V transformer, and biased with ultra low noise power supplies. The tube used is the best sounding tube from the super tube family of tubes – the E280F. The triode is loaded with a special quality large core step down transformer. The tube power supply is an oversized choke regulated supply, making sure that the tube is up to the task of following the converter’s flashing dynamics. Furthermore, the step-down transformer reduces the output impedance to 55 ohms, with a maximum swing @ full scale of 30V pp sine wave (10V rms).

SPECIFICATIONS
20 R2R converters per channel, complimentary current output
using the top grade AD1865N-K , 10 converters per bank, 20 per channel,40 in total
Output range: – 30Vpp output @ 0db. 10V rms (5V rms on -6db setting).
Eight discrete ultra-low-noise regulators for the 4 converter banks User selectable output using rear switches: 10v @50ohms or 5v @12ohms.
Extensive local decoupling,using tuned LC filters. Output: 2 x RCA with a true balanced output as standard. Floating RCA output switchable (ground loop resolver).
Over engineered power supplies, power input filters. Output impedance: ~50ohms (balanced and SE output), 12ohm at -6db setting.
Transformer I/V conversion with custom wideband transformers, balanced current to  single ended voltage conversion. USB input: up to 24/384KHz including double reclocking.
Internal Super-Clock bypassable on the fly. Separate toroidal transformer,triple regulated supply Jitter attenuation: down to femtosec level.
Transformer loaded super tube output stage using the E280F tube. Dimensions: 540mm W x 520mm D x 165mm H.
5:1/10:1 step down transformer & double choke filtered supply. Weight: 80kg (total).