OPA861 zero-feedback output stage of AYA II

It is the holiday season, so for those still not familiar with Audial devices’ sound qualities, but with some time and will to solder, here is the idea on how to use them. The result might be both good sound, and a better understanding of audio issues.

So, here is the output stage of AYA II DAC, released back in 2007, now with details of the circuit behind the originally posted block diagram.

out

Overall, it lacks the ultimate linearity of output stages used in the Model series and Gramofone DACs – Audial latest no compromise I/V circuit distortion figure, when used with PCM1704K, went below 0.0005% (-110 dB, and no feedback, yup) – but subjectively it still fares really well. OPA861 internal circuit is for this purpose almost unbeatable diamond architecture, with the benefits of on-chip transistor matching. In fact, its sonic properties still could outperform any other published I/V circuit, as also found by some devotees earlier, when AYA II was available as an offline DIY project, namely by Elso Kwak and by Hen-Hsen Huang.

The circuit as such is intended for use with TDA1541(A), but it should be pretty easy to accommodate it to any other D/A chip. It is well-proven for its operation reliability, and this document’s data should be sufficient too. However, please be kind and note that currently we can not really support DIY endeavors, and consequently we probably won’t have time to address any questions you might have on this matter.

You must be logged in to download this PDF.

6 replies on “OPA861 zero-feedback output stage of AYA II”

  1. Really a great design. I still use it in my main DAC.

    Thank you for your effort and sharing. Now I can introduce my friends to this unique I/V.

  2. Hi Pedja!
    I want to build your I/V stage based on OPA861 and have a question. On the schematic you use two different ground-symbols, the one at the 2n2 cap is special. Does this mean that the cap should be placed close to the TDA1541? and how do you want the two gounds to be connected?
    Thanx in advance
    Thorsten Larsen

  3. Hello Thorsten.

    Yes, you are correct.

    These two ground symbols are not entirely standardized. Usually, the symbol you mostly see on this schematic is used for earth ground, while the symbol used for 2n2 ground is used for circuit ground. However, these two symbols are also used as a rescue in mixed circuits schematics, to point out the difference between digital and analog ground.

    In this case, the 2n2 ground symbol is different because this cap essentially belongs to the TDA1541(A), where it keeps the impedance the TDA output sees low, at highest frequencies – this stage as such does not really need it. Hence this cap’s loop should be closed with respect to the TDA ground, and it means here its analog ground (pin 5).

    Still, if you keep the overall layout (i.e. ground paths) tight, this might not be that significant issue. Which might be an answer to your second question: ideally, these two stages should be close to each other, with reliable, low impedance ground path in between.

    (BTW, please don’t try to use such a cap with conventional opamp I/V, as the capacitance at opamp inverting node will make it oscillate.)

    Regards

Leave a Comment

 

Scroll to Top