@danny92 to share a bit more information about the OPA861 I/V, it is based on Pedja Rogic's zero-feedback output
https://www.audialonline.com/blog/opa861-zero-feedback-output-stage-of-aya-ii/
https://www.audialonline.com/blog/opa861-zero-feedback-output-stage-of-aya-ii/
I said I tried it on DDDAC, similar story, maybe not as dramatic. 🤣
Why do you even bother with those capacitors that are not needed at all for active I/V, in the case of passive I/V they are desirable and should be calculated depending on the used resistor because then it is a low-pass filter. Even with a dddac a 15nF capacitor should have no effect on the sound.
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Thanks to everyone who helped with answers and especially to @miro1360 for the custom designed board, and all his work in this thread. The AD1862 board was installed in my 'hotrod' ANK DAC, along with two power supplies and an HDMI input board. I look forward to hearing it open up as everything 'settles in' 🙂
OK. Already back with a question.... Just sat down to listen a bit more carefully to the new board. At 44.1k it sounds great,at 96k there is a little static sound, seemingly along the louder passages. 192k is mostly noise/static. I tried searching the thread but nothing obvious came up. Could it be a grounding issue? I presume that any I2S wire mixup would not allow it to play music nicely at 44.1? I also note the sound stage is quite narrow in 44.1 vs 96k.
Cheers, Soren
Cheers, Soren
Congratulations on the finished DIY DAC, but you have one big problem in the middle of the DAC which is the mains transformer which is too close to the tubes themselves, the I/V transformers and the audio part in general.
This seems to be normal today that mains transformers are placed everywhere in the box, if you look at any factory device you will see that in most cases mains transformers are on the left side and the most sensitive components with audio signals on the right.
Thanks! You are absolutely right. I need to reorganize the layout and will likely spring for a slightly larger chassis to get the mains transformers away/shielded from the rest of the boards.
I had neglected the I2S ground connections and adding those solved the static problem. Maybe my 'conversation with myself' will be helpful to a future builder 🙂
It has an effect on the sound, I tried it and gave up. It was in the first version of the DDDAC with capacitors on the output to block the DC voltage. By adding an output transformer, I got better sound, noise filtering, SE and balanced outputs from the same transformer. Since I will no longer invest in DDDAC, these transformers remain. I experimented a lot, tried a bunch of transformers until I found the good ones. Doede uses Sowter custom transformers which are quite expensive, plus postage, customs and VAT. 😒
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Can anyone explain why this DAC was originally design with silver mica small caps before and after the I/V transformers, in addition to the I/V resistors? Do they serve as a high frequency filter, prevent ringing? Removing one or both pairs significantly dials up the highs and adds detail/air (and listening fatigue).
Cheers,
Soren
Cheers,
Soren
It's really strange, with passive I/V I used 15nF in parallel with 50ohm without any effect on the sound and the PCM1702 was used which has a much smaller output current than the PCM1794.
For example, Thorsten Loesch for pasive I/V recommended 33nF and 100ohm(maximum) for PCM63.Therefore for the PCM1794 which has a much higher current than the PCM1702 or PCM63 a capacitor larger than 33nF should have no effect on the sound.
I don't know why but my shift registers don't work, I'm using the 74HCT164E, the clock and data inputs seem ok, but the register output values remain the same all the time, what could be the issue?