Mr White's "Opus", designing a simple balanced DAC

[luvdunhill]

Originally Posted by Russ White

One of which was certainly something like that. I also though about using something with galvanic isolation.

Russ, I think I'll just try the hex inverter approach. I do have a question though, is the DSD signal 3.3V or 5V TTL, and which does the Opus prefer? I'm assuming they are compatible, since you directly connected them. I'm just wondering if I need a 5V or 3.3V supply for the hex inverters (or perhaps a buffer cannot be used for level shifting anyways? I'm rather new to this.) I'm looking to use TI SN74HCU04D.



Also, any recommendation on the input caps? Similar application notes I've seen, said they should be used. I was thinking np0 ceramic or similar? I was also thinking about adding a nearby LP2985 and a few caps, as you did on the Opus.

[glt]

According the Wolfson, the WM8741 (OPUS) is NOT 5V tolerant...

[BrianDonegan]

Correct. Opus uses 3.3V for VD and 5V for VA. You will need too use 3.3V for anything digital.

[m.massimo]

I've got a problem, I fear the module has gone but I accept some suggestions.
My setup:
-2 Opus 8740 based modules in mono mode
-1 spdif receiver module
both dac modules share the ps, analog and digital separated (8Vdc), receiver has its own ps.
-Broskie Cathode Follower output stage bal->se

I noted a low volume from left channel yesterday, a rapid check with the scope showed that pins 13 (VOUTRN) and 17 (VOUTLP) in left channel module are mute, so the output stage delivers a 0.5*V signal (1.15Vpp against 2.3Vpp, less than balanced output due to output stage <1 gain).
This condition is true with stereo mode, mono left mode, mono right mode. In stereo mode the signal on 13 and 16 pins is not a complete sine wave (see picture). The other two modules are ok.
I think the 8740 is partially dead, but I'm glad to hear any ideas from you about it.
If the 8740 is dead, is there any chance to swap the IC with a fresh one?
I can set the working module in stereo mode and starting again, but I'm curious to understand what happened.
Thanks.

[BrianDonegan]

It does indeed look as through the chip is dead. As to what happened, it is hard to say.

Is your output stage healthy?

[Erlend Sæterdal]

I changed the Lp 2985 for the 5 V to New Class D regulator and removed the ferrit perles and ceramic capacitor because the Dac was Screaming at me

What a difference.

[m.massimo]

Originally Posted by BrianDonegan

Is your output stage healthy?

Thank Brian for your reply,

yes I think so, I'm using the remaining good module in stereo mode now and everything is going smooth. I listened a couple of cds last evening and I should say I prefer the dual mono setup in terms of sound quality especially in the high frequencies.

I suppose it's not a good idea to mix 8740 and 8741 based modules in a new dual mono setup. What do you think?
Is there any chance to replace the dead IC or I've to consider the whole module dead?


in my previous post there was a typo
"....stereo mode the signal on 13 (read 12) and 16 pins is...."

[gazzagazza]

Just a heads up. I had a mains transformer supplied with my Opus parts fail on me recently. It ignited internally. Fortunately it caused the windings to go open circuit so there was no major fire.

[Luke]

nice little opus usb dac is finished.
Here it is next to my F4 HP amp.

[Russ White]

Nice work Luke!

I bet that combo sounds great.