R2R | DIGITAL TO AUDIO CONVERTER
The Ianus Series Ithaka Digital to Audio Converter mates our Triode Fet gain stage and completely redefines the status of digital replay
“…What if we used an evolved version of a SOTA digital engine ,like the one used in our Kassandra LE, and “slap” an output stage based on our latest generation of the TriodeFet technology . Well we tried it… and ended out with developing our newest digital source to come out of AC labs.The Ithaka is the result of our curiosity , about combining some of our technologies we are very proud of..”
DESIGNER
The Ianus Series Ithaka Digital to Audio Converter mates our Triode Fet gain stage and completely redefines the status of digital replay.
Designing the Ithaka
The Ithaka d/a converter spawn out at the same time we developed our new generation of our TriodeFet technology ( new Gen developed as showcased in our QuintEssence amplifiers), and was not a coincidence. Our top line-level technology, the Inverted Triode is already used in our flagship converter , the Homerus. However, mating one of our top digital banks , to our current top med-high power technology, the TriodeFet, was an idea that was on paper but not on our immediate plans. However, some experimental prototypes demonstrated and easily convinced us that this new technology has to become available..now.
Fast forward, the Ithaka is proudly out.
The Ithaka is a ladder DAC. Typically a ladder DAC uses a resistor network switched by a N number of switches, N being the bit depth. It is a passive sort of speak procedure with no manipulation of the incoming data stream.
It also has no digital filter, and completely avoids the negative sonic aspects created by fitting the common Delta-Sigma or Multibit architecture.
In the case of the Ithaka we choose to use an R2R IC – the classic Analogue Devices AD1865N-K, a much praised chip which we believe is the best sounding IC ever made. No less than 24 R2R converters per channel. 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 in our converter system.
The input data is latched and directly refreshes the resistor network, with absolutely no additional complex logic or data handling/processing. This way we have full control over the resistor network to use it as part of our converter system. Our Super Clock circuit directly re-clocks and drives the “refresh” signal, so absolutely no additional jitter is induced in the conversion.
There are no less than 24 R2R converters per channel in the Ithaka working as parallel switched resistor ladder converters, cancelling the deviation of resistor values down to Zero. Paralleling R2R converters improves linearity and noise figures are improved on the same principles, along with the dynamic range and channel separation. Sonic wise, paralleling converters elevate performance to another level in all aspects significant in high end audio.
Jitter
In the Ithaka we use many techniques regarding lowering and cancelling jitter, in both passive and active ways. Bouncing signals, overshoots, low rise times etc greatly increase jitter. We solve this by using special driving circuits and carefully tuned digital line terminations for all digital signals.
We use 70 LC filters implemented using RF chokes and high speed capacitors to decouple digital circuits and ICs from the power rails. These are extremely effective in cancelling out any form of PSU sourced jitter and solve this fairly complex problem. Jitter originated in USB and S/PDIF / Toslink sources are eliminated right at the “refresh” signal of the converters.
Having an IC that has no complex data handling logic and no multi stage data logic, the precisely timed signal resolves in a extremely accurate jitter free conversion. In our opinion, this is not possible with any other type of converter system.
The Super Clock is also used upstream for re-clocking the XMOS asynchronous USB controller, as well as the SPDIF receiver. With the internal clock, there is no need for a word clock input.
Jitter present at the word clock of the transport before S/PDIF transmission to the dac. Almost identical Jitter measurement was also present at the word clock using a USB transport.
Jitter distribution measurement of the word clock synchonising the 16 converters of the Kassandra DAC with the internal reclocker enabled, and using the same USB transport.
Jitter distribution after double reclocking of the word clock.
I/V Stage
The R2R ICs are current output devices. Their impedance is very high and close to an ideal current source. To drive the next stage in the Kassandra, the current must be converted to voltage. Avoiding using sonic degrading Opamps or a simple resistor, we use a specially designed transformer that converts the current differential to a single ended voltage output. The specially designed transformer is an ideal solution, and is second to none in direct comparison to the many alternative I/V methods available.
Gain Stage
The crown jewel of the Ithaka concept , is the output stage. This is based on our latest generation of our TriodeFet technology (the specific TF generation is only used in our top SE amplifier, the QuintEssence).
The output stage is Single Stage-Single Ended circuit, and it’s ultra wide-bandwidth , extreme linearity allows the digital bank qualities to shine through.
With an output impedance of 1 ohm, the output stage is as potent of a speaker amplifier, as it can deliver 12W if the converter it directly connected to any speaker. It is however not the D/A purpose to be used as power amplifier, however is a sample to it’s output stage potency.
(During developing, the d/a was used to drive speakers directly allowing us to perfectly tune and evolve the sound of the Ithaka.)
The Power Supply
The Ithaka d/a is powered by it’s external Power Supply Unit.
All separate digital/analog circuits, TriodeFet and bias circuits are powered by very low impedance, passively filtered independent PSUs, with multiple-stage cascaded filters.
Ultra high quality inductors and capacitors filter out low and high frequency noise for unprecedented quiet power rails.
The TriodFet stage is powered by a triple choke filtered high energy/high current PSU.
Two low noise 500VA transformers power all stages through very low noise Schottky SIC discrete rectifiers.
Technical Specifications
DIGITAL SECTION | |
IC Chip Array: | 24 R2R converters per channel, complimentary current output using the top grade Analogue Devices AD1865N-K with 12 converters per bank, 24 per channel, 48 in total |
Current to Voltage Conversion: | Transformer I/V conversion with custom wideband transformers, balanced current to single ended voltage conversion. |
Additional Clock: | Internal Super-Clock by-passable on the fly, triple regulated supply, quad-stage pre-filters |
Regulators: | Eight discrete ultra-low-noise regulators for the 4 converter banks,quad-stage pre-filters |
POWER SUPPLY SECTION | |
PSU: | Massively over engineered power supplies, power input filters |
PSU filering: | Extensive local decoupling using tuned LC filters |
Mains Transfomers: | 2 Low noise 500VA torroidal transformers, over 4 Farad total system capacitance, wideband local decoupling |
Pseudo-battery system: | Four independent Pseudo-battery systems for isolating all analog and digital stages from the power grid, Quad-stage pre-filters |
TriodeFet PSU: | Triple choke-filtered, veru high current capacitor supplies |
INPUT & OUTPUT SECTION | |
Gain Stage: | Third Gen TriodeFet output stage, Single-Stage, Single Ended circuit. 1A idle current Class A operation. |
Output Range: | RCA: 30Vpp output @ 0db 10Vrms |
User Selectable Output Tuning: | User can pre-load the output stage using external resistive modules, to fine-tune the sound. |
Output: | 2 x RCA, 2 x Balanced. True Balanced output standard. |
Output Impedance: | 1 ohm (balanced and SE output). |
USB input: | Data rates up to 24/384KHz |
Other inputs: | AES/EBU, S/PDIF, BNC. |
Jitter attenuation: | Down to femtosec level |
Dimensions: | 540mm W x 580mm D x 165mm H |
Weight: | 160kg total unpacked |
