As implied by its name, the AYA II had its prehistory in Pedja Rogic's TDA1541A DIY DACs published between 2003 and 2006. The first two were open source projects and full DIY info was publicly accessible. Experience with such an approach however wasn't entirely good, since these projects served not only for DIY but also for unauthorized commercial gain. The third project (original AYA) was hence very restrictive in bringing info publicly available; the actual project has been originally shared only with PCB users, and it only recently (as of May 2008) became available online.
Approach with this project is somewhere in between. So, you'll find here a bit more on the general topology of the AYA II, but complete project documentation access will be still limited to the actual customers. The DIY kits are offered, and you can place an online order.
So you'll find here somewhat more technical information on AYA II than at main Audial site area.
Still, it is highly recommended to read the text posted there as well. Of course, if you rather do not admire DIY, you can simply buy completed device.
S/PDIF input stage
Just as its predecessor, the AYA II uses CS8414 S/PDIF receiver. This part is now getting out of production so it may become hard to obtain soon, however the whole Crystal's CS841x series is capable of extremely good jitter performance, down to 50ps peak-to-peak (this was nicely pointed out by John Westlake in his graphs posted to DIYHiFi.org), even if manufacturer's data sheets don't claim this good figure (200ps RMS).
Rather than using reclocker as in the first AYA DAC, which indeed brought important improvement in many aspects of subjective performance but still didn't alleviate the need for use of the good transport, we settled on getting the most out of the receiver as such, and for this reason discrete low noise regulators are now feeding this part too.
The input is transformer coupled and differentially terminated. Pulse Engineering transformer is employed instead of the previously used Scientific Conversion, since it performs very well and is both cheaper and easier to source than SC. Anyhow, footprints are the same so one can use the part of own choice.
USB decoder
USB input is based on Burr-Brown PCM2706 decoder which provides I2S output. Additional low jitter oscillator feeds its PLL. This stage is supplied by low impedance shunt regulated voltage, distributed to the individual parts of PCM2706 via RC filters.
D/A part
The two sources are switched by RF relays. One of them switches off also the ground of USB stage, to isolate it from the rest of the audio chain while USB is not in use.
The AYA II uses venerable Philips TDA1541A D/A converter chip, which is supplied by low noise, wide bandwidth, discrete regulators with excellent transient performance. As opposed to the first AYA and as shown on the picture below, the AYA II is using SMD polyphenylene capacitors for TDA1541A active divider decoupling.
Output stage
The diagram below shows the general topology of new output stage based on Burr-Brown OPA861 chip, colloquially named a transconductance “opamp”. OK, we know that we won’t talk opamps unless feedback is employed, and here it is not; a "super-transistor" may sound like a marketing hype but it fact it designates the part far better. As seen from the outside, this chip retains all the functional features of single transistor, with improved performance.
The "emitter" input of OPA861 provides low impedance source/sink for the output current TDA1541A (its unipolar output is nullified by additional 2mA current source), and this impedance is equal to 1/Gm. So with transconductance equal to 120mS (@ Iq=7mA) it is about 8 Ohm. This output current of TDA1541A thus modulates the OPA861 "emitter" current and the same current is transferred i.e. mirrored to the "collector" of OPA861, where I/V resistor provides a low impedance path to the ground. Voltage at this point is thus equal to this current times the value of the resistor itself, so with 1k5 we get close to the typical 2V CD value (6V peak-to-peak i.e. 2.1V RMS).
Another OPA861 is used like an open loop voltage buffer. The OPA860, which is a buffered equivalent of OPA861 is not employed because its buffer uses a feedback (as opposed to its own predecessor, OPA660). The output is capacitively coupled.
Please note that the drawing below shows simplified circuit only. (Please, click on the drawing to enlarge it.)
Kits
Three AYA II DIY kits are offered to suit specific needs, and these are the full kit, S/PDIF only kit and USB only kit. Each kit includes adequately populated and tested board, and custom wound mains transformer. You would need a chassis and chassis mounting connectors and switch(es) to complete the unit.
• The AYA II DIY full kit. Two items are shipped:
Fully populated Printed Circuit Board
It is the 14 x 16.5 cm, double sided board, with solder mask and silk screen. The quality of PCB manufacture is up to task by current standards, and quality of the layout is way above them. All the PCB mounting parts, including BNC and USB connectors are populated.
Mains transformer
This is the custom wound 40VA toroidal transformer comprising seven required secondary windings, with electrostatic screen and outer electromagnetic shield. Primary is bifilarly wound so it is both 110-120VAC and 220-240VAC compatible.
• The AYA II DIY S/PDIF kit. This kit comprises also the PCB and mains transformer but the board doesn't comprise the parts associated to the USB input.
• The AYA II DIY USB kit. This kit comprises also the PCB and mains transformer but the board doesn't comprise the parts associated to the S/PDIF input.
Either kit includes complete AYA II DIY Assembly Manual.
To place an order, please visit this page.
