Hello, new to this side of the forum, mostly hang out on the tube side 🙂
I'm planning on integrating a USB DAC into another project, I looked around and found a lot of stuff about the PCM27xx chips but they are long since discontinued and seem a bit hard to get so I was thinking of using the PCM2900c for my project.
My question is whether I should use the analog output of this chip directly or if you think I'd be much better off using it as a USB to I2S interface to feed to another DAC chip(if so, which chip?). Output power is somewhat unimportant as there will be an amp stage after this 🙂
The main reason I'm asking is because the PCM2900 "only" has a 16-bit DAC and 48KHz sample rate max, 16-bit seems pretty alright but 48KHz seems a bit low for a high quality DAC(most projects I've seen are well over double this speed)?
I'm planning on integrating a USB DAC into another project, I looked around and found a lot of stuff about the PCM27xx chips but they are long since discontinued and seem a bit hard to get so I was thinking of using the PCM2900c for my project.
My question is whether I should use the analog output of this chip directly or if you think I'd be much better off using it as a USB to I2S interface to feed to another DAC chip(if so, which chip?). Output power is somewhat unimportant as there will be an amp stage after this 🙂
The main reason I'm asking is because the PCM2900 "only" has a 16-bit DAC and 48KHz sample rate max, 16-bit seems pretty alright but 48KHz seems a bit low for a high quality DAC(most projects I've seen are well over double this speed)?
PCM2706 still active on TI's site.
Whether I'd recommend the on-chip DAC depends on your aspirations for sound quality. I'd want a bit better SNR than 95dB myself even for 16bit material.
Whether I'd recommend the on-chip DAC depends on your aspirations for sound quality. I'd want a bit better SNR than 95dB myself even for 16bit material.
That may be true but I can't source them for assembly through any of the PCB fabs I use whilst the 2900 is available in hundreds or thousands quantities 🙃
My aspiration is something better than what you'd expect from your phone or computers usual headphone jack I guess? I don't really have much experience with DACs so it's a bit hard for me to say. The amp isn't going to be overly fancy, probably close to those ~€100 tube + solid state jobbies(not that I've heard any of those myself, but the planned amp is a similar topology 🙂 )
Nowadays you'd be unlikely I think to find as poor a DAC as in the PCM2900 in any half-respectable phone.
I have a 16bit DAC design which sounds better than any of my phones : https://www.diyaudio.com/community/threads/toscanini-nos-dac.389937/#post-7188755. But its a whole separate PCB and you might be looking for a more compact solution.
I have a 16bit DAC design which sounds better than any of my phones : https://www.diyaudio.com/community/threads/toscanini-nos-dac.389937/#post-7188755. But its a whole separate PCB and you might be looking for a more compact solution.
Good to know, that probably puts using the Pcm2900 on its own in the trash eh? Not much point if it's better quality to just run a 3.5mm cable instead of USB 🙂
That's quite a nice project, don't quite understand why you use so many TDA1387s though..?
Correct me if I'm wrong but that DAC takes I2S input rather than USB? And has an included amplifier on the PCB? If so, I could use the PCM2900 for a USB to I2S interface and do a similar thing except skipping the amp part?
Why I use so many TDA1387s? Because it sounds better with more. A single TDA1387 has an SNR in the region 95dB but when you parallel them the SNR improves by 3dB for each doubling of the number of chips.
Yes the Toscanini takes I2S (native interface format of TDA1387). There isn't an amplifier as such but it probably could drive some high impedance headphones at a pinch. I assume by 'amplifier' you mean a speaker amp? Or do you just mean a circuit to take the DAC chip output up to standard CD line level (2VRMS)? If the latter, then yes it has that.
Yes the Toscanini takes I2S (native interface format of TDA1387). There isn't an amplifier as such but it probably could drive some high impedance headphones at a pinch. I assume by 'amplifier' you mean a speaker amp? Or do you just mean a circuit to take the DAC chip output up to standard CD line level (2VRMS)? If the latter, then yes it has that.
I ment the latter with an amp 🙂 alright thanks for the explanation. I have looked around further and found that the board houses I frequent have the PCM1794A available so right now I'm thinking I'll use the PCM2900 for USB to I2S(unless someone can suggest a more suitable chip for this) and then a PCM1794A for I2S to analogue and then into the amp it goes. Does that sound good?
The PCM1794A is far from cheap though so any cheaper alternatives would be appreciated for my poor student wallet 🙃 this DAC part of this project is starting to get about as expensive as the amp part haha
PCM1794A certainly is a very large jump above PCM2900 in quality. However its not a complete solution, you still need to add on your own opamp output stage because that device is a current-out one. There are other chips not quite as good as 1794 which are one-stop solutions, PCM5102 comes to mind. That's likely to be cheaper and no need for extra opamps.
IMHO PCM5102 is a very good choice for PCM27xx/29xx - it is simple and inexpensive itself and does nor required sophisticated power supply. It will be much better than using 2900's internal DAC.
As PCM27xx/29xx operates in UAC1, with a limited samplerate, and which is more important - use adaptive sync (instead of asynchronous sync in newer USB interfaces, like XMOS, Amanero, CMedia, ComTrue, etc.), using PCM1794 and similar (AK44xx, ESS90xx) will be huge overkill.
As PCM27xx/29xx operates in UAC1, with a limited samplerate, and which is more important - use adaptive sync (instead of asynchronous sync in newer USB interfaces, like XMOS, Amanero, CMedia, ComTrue, etc.), using PCM1794 and similar (AK44xx, ESS90xx) will be huge overkill.
Thank you so much for this suggestion! The specs seem absolutely excellent and the price is very low compared to the PCM1794! 32-bit even (though that's well beyond useful I belive)!
Interesting point about the USB side though, I picked the 2900 because it would just work with no drivers on all platforms, but is there a better pick there too perhaps? I looked around a lot but like mentioned in the OP, this seemed like the chip to use 🙂
Cheap options for USB are CMedia CM108 and CM102, the latter though only comes with S/PDIF output so would need an additional S/PDIF decoder chip.
Today (since the UAC2 driver was implemented in Win10), almost all USB Audio interfaces works without the special drivers on all platforms (unless you need ASIO or special features).
Nice! The CM108 seems like a good alternative for me. Not quite as good of a datasheet but seems like it is just as up to the task as the PCM2900 whilst being much more affordable 🙂
picking up this project again, now with the desire for 24-bit and 192kHz, but the CM and PCM chips discussed here only do 48kHz, i didnt really find anything resonable when poking around the web on my own so i return here for further help.
Is there a readaly available chip that will do USB to I2S at 24-bit 192kHz? Preferably in stock at JLCPCB but thats just a nice to have 🙂
Is there a readaly available chip that will do USB to I2S at 24-bit 192kHz? Preferably in stock at JLCPCB but thats just a nice to have 🙂