As already told and as suggested 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 use. The third project (original AYA) was hence very restrictive in bringing the info publicly available; the actual project has been shared only with PCB users. [As of May 2008, it became availble online though.]
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 limited to the actual customers. The DIY kits are offered and you can place an online order.
S/PDIF input stage
Just as its predecessor, the AYA II uses CS8414 S/PDIF receiver. This will be probably our last unit using this part, since it got out of production and may become hard to obtain soon. Its advantages are however well documented and only marketing speech discards it easily. In fact 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 performance (200ps RMS). Also, other than CS8412 they all lock on preamble, being thus relatively free from the data related jitter.
Rather than using reclocker, 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 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
The AYA II DIY kits are offered and these make possible to build AYA II by yourself, and without headache because of hard to find parts. A couple of kits are offered to suit specific needs.
• The AYA II DIY full kit. It comprises practically completed DAC without the chassis and chassis mounting connectors and switches. 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 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 proceed with the order, please visit this page.
