“…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 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…”
“…and what if ,we design the smallest TriodeFet d/ac possible, how close could that be, to the bigger brother.?..” Ithaka minor is born - Stavros Danos, Designer
 
Designing the Ithaka/Ithaka minor
 
Originally, Ithaka d/a converter technology was created at the same time we developed the new generation of our TriodeFet technology (new Gen developed as showcased in our QuintEssence amplifiers). 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 quickly convinced us that this new technology has to be made available.
 
Fast forward, the Ithaka is proudly out.  Its smaller sibling the Ithaka minor followed soon after. The main goal when designing the Ithaka minor was achieving the Ithaka’s sonic attributes and strengths as closely as possible, but on a smaller footprint. The project begun as an exercise of designing the smallest possible TriodeFet-output d/a. However minimum complexity issues limit the smallest form/size that can be achieved. The Ithaka minor is the smallest TriodeFet (though not small by any means) converter coming out of our labs.
 
The Ithaka/Ithaka minor are ladder DACs. 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/Ithaka minor, we choose to use an R2R IC – the classic Analogue Devices AD1865, a much praised chip which we believe is the best sounding IC ever made. No less than 12 R2R converters per channel. The AD1865 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.
 
The Ithaka minor differentiates itself to its bigger brother by the configuration, and number of converter banks used. Where as the Ithaka uses two 12 (in parallel) converter banks in differential mode , per channel, the Ithaka minor uses a single 12 (in parallel) converter bank, in single ended mode, per channel.
 
The use of parallel switched resistor ladder converters, aim in 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.
 
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 Ithaka minor, 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.
 
The Ithaka minor uses different configuration for the I/V transformers, unique in our d/a range. This was necessary and at same time a nice evolution in our I/V tech, as in contrast to our other top models, the converter banks are in Single Ended mode.
 
Gain Stage
 
The crown jewel of the Ithaka / Ithaka minor concept is the output stage. Contrary to the bigger Ithaka model, the Ithaka minor is using the Gen1 TriodeFet technology. This particular generation of the TriodeFet is the same used in our Essentia and Aperio amplifiers, with some modifications.
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.
 
The Ithaka minor, though having a smaller output stage than the Ithaka, still boasts  an output impedance of 1 ohm, and has an output stage as potent as a speaker amplifier, delivering 8W if the converter is directly connected to any speaker. It is however not the d/a purpose to be used as a power amplifier, rather this is a sample of its output stage potency.
 
The Power Supply
 
The Ithaka minor is borrowing the PSU architecture from it’s bigger sibling, though smaller in size and potential.
 
As in all out top model d/ac, the Ithaka DAC is powered by its own external Power Supply Unit. And like the bigger model, 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 400VA transformers power all stages through very low noise Schottky SIC discrete rectifiers.