SCK and BCK, audio caps
Very good points, thank you. And all correct you have mentioned!
1) SCK and BCK:
Yes, true, both are connected to each other (RPi does not provide SCK, just a three signal I2S). But IT WORKS! For sure: I tried, and also these guys did: DDDAC 1794 NOS DAC - Non Oversampling DAC with PCM1794 - no digital filter - modular design DIY DAC for high resolution audio 192/24 192kHz 24bit
What really happens inside - no idea, sorry. Potentially (based on datasheet) it is a bit wrong (and 'against' datasheet):
with 48 KHz and 24bit - and RPi will play as 32bit (per channel, use RPiDAC driver) - we have just 64 fs (48 KHz, 32bit stereo results in 3.072 MHz SCK instead of 6.144 MHz for 128 fs). If it results in 1/2 effective fs (48 KHz is played like 24 KHz) or if the DAC would do "averaging" (or "dithering") between two consecutive PCM words, the filter characteristics do not match with datasheet ... no idea, sorry. It works, for sure, it sounds great and is the only way to use in a simple way on a Raspberry Pi (otherwise use a FPGA/CPLD and generate SCK from BCK, so you could add also a PLL ;-) ).
2) audio caps:
Sorry, I am not an expert. There is a big discussion which caps to use in audio signal path. I am potentially wrong, sorry. The message I tried to provide: check a bit which caps (which dielectricum) when fighting for best audio.
Thank you for the correction, I appreciate.
(I go often with high voltage ratings on such caps, but true: some types might be worse due to voltage dependencies, I agree. And my thought: SMD caps are even better as large through hole MKT: less parasitic inductance).
Anyway a valid point: check which type of caps are best for audio signal path.
Thank you for correction and pointing out.
Very good points, thank you. And all correct you have mentioned!
1) SCK and BCK:
Yes, true, both are connected to each other (RPi does not provide SCK, just a three signal I2S). But IT WORKS! For sure: I tried, and also these guys did: DDDAC 1794 NOS DAC - Non Oversampling DAC with PCM1794 - no digital filter - modular design DIY DAC for high resolution audio 192/24 192kHz 24bit
What really happens inside - no idea, sorry. Potentially (based on datasheet) it is a bit wrong (and 'against' datasheet):
with 48 KHz and 24bit - and RPi will play as 32bit (per channel, use RPiDAC driver) - we have just 64 fs (48 KHz, 32bit stereo results in 3.072 MHz SCK instead of 6.144 MHz for 128 fs). If it results in 1/2 effective fs (48 KHz is played like 24 KHz) or if the DAC would do "averaging" (or "dithering") between two consecutive PCM words, the filter characteristics do not match with datasheet ... no idea, sorry. It works, for sure, it sounds great and is the only way to use in a simple way on a Raspberry Pi (otherwise use a FPGA/CPLD and generate SCK from BCK, so you could add also a PLL ;-) ).
2) audio caps:
Sorry, I am not an expert. There is a big discussion which caps to use in audio signal path. I am potentially wrong, sorry. The message I tried to provide: check a bit which caps (which dielectricum) when fighting for best audio.
Thank you for the correction, I appreciate.
(I go often with high voltage ratings on such caps, but true: some types might be worse due to voltage dependencies, I agree. And my thought: SMD caps are even better as large through hole MKT: less parasitic inductance).
Anyway a valid point: check which type of caps are best for audio signal path.
Thank you for correction and pointing out.
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You shouldn't have posted that link ((
I need to finish my current project before starting a new one :]
And thanks so much for the NP0 recommnedation - I would have definitely missed it and went the wrong way. Just ordered these.
((I need to finish my current project before starting a new one :]
And thanks so much for the NP0 recommnedation - I would have definitely missed it and went the wrong way. Just ordered these.
Or simply drop in a src4192/ad1896 with a local clock. That would also clean up the pretty bad clock from the Pi. A resampler has also the advantage of defining once for all the operation of the DAC and thus of the analog filter.
The DDAC is a bit of a different beast as it doesn't use the digital filter section of the pcm1794. I'd rather not comment further on it as I think it does almost everything wrong.
http://www.audioxpress.com/assets/upload/files/negro3051.pdf
The Metronome ASRC Module (check the schematic and manual)
The Metronome ASRC Module (check the schematic and manual)
IT WORKS!
Try#1 missed one via and one op-amp section was not getting -15V, though getting +15V rail. A puff of smoke and a run around the city to get replacements (of course they had to discontinue LME49990 right during these days :] ). Managed to find them, replaced, got 3 extra spares just in case.
Try#2 Just a random noise from loudspeakers. Believe it or not, failed to connect GND between RPI and PCBs :]
Try#3 Voila!
I took balanced output right after I/V section and fed them into my Hegel amp balanced input. It does sound fantastic, I don't have many in my list, but this project clearly outplays every DAC I've heard and tried in my system. Whatever the intensity of the track - it always feels there is still so much headroom left. So excited with so many music to go through :]
Some points:
1) Will have to put everything in a nice enclosure and arrange all the cabling, shielding, etc - will keep it posted here. Together with questions, I guess :]
2) I plan to integrate WaveIO board as an additional USB input option. How do I best switch the signal? Mechanical switch with 3 contacts? That would make quite long runs of I2S signal wires (rpi/waveIO -> switch in panel -> back to PCBs), is it ok? Maybe some kind of electronic solution? Mosfets/CD4053 IC? Won't it influence the signal?
3) LME49990 seem to heat up quite a lot, is it normal? So far managed to get away with several DC fans around the boards, but as is - they definitely need a heatsink. Haven't found anything about that in a datasheet, so trying to make sure that they really do need it and it's not a fault in assembly of sorts (which is doubtful, since everything works great).
Try#1 missed one via and one op-amp section was not getting -15V, though getting +15V rail. A puff of smoke and a run around the city to get replacements (of course they had to discontinue LME49990 right during these days :] ). Managed to find them, replaced, got 3 extra spares just in case.
Try#2 Just a random noise from loudspeakers. Believe it or not, failed to connect GND between RPI and PCBs :]
Try#3 Voila!
I took balanced output right after I/V section and fed them into my Hegel amp balanced input. It does sound fantastic, I don't have many in my list, but this project clearly outplays every DAC I've heard and tried in my system. Whatever the intensity of the track - it always feels there is still so much headroom left. So excited with so many music to go through :]
Some points:
1) Will have to put everything in a nice enclosure and arrange all the cabling, shielding, etc - will keep it posted here. Together with questions, I guess :]
2) I plan to integrate WaveIO board as an additional USB input option. How do I best switch the signal? Mechanical switch with 3 contacts? That would make quite long runs of I2S signal wires (rpi/waveIO -> switch in panel -> back to PCBs), is it ok? Maybe some kind of electronic solution? Mosfets/CD4053 IC? Won't it influence the signal?
3) LME49990 seem to heat up quite a lot, is it normal? So far managed to get away with several DC fans around the boards, but as is - they definitely need a heatsink. Haven't found anything about that in a datasheet, so trying to make sure that they really do need it and it's not a fault in assembly of sorts (which is doubtful, since everything works great).
This is a classic and often used (though expensive) concept of channel separation. In general, you don't want anything happening in one channel affecting the other. If they share same power source, voltage drops due to to the loads in one channel affects the voltage another one is receiving.
Hi,
I am interested to build this DAC too, but have some questions and seeking for help.
1. LME49990 has been discontinued already. I am thinking of replacing the opamp to AD797 or ADA4627, any comments?
2. Why 12 x opamps are needed? Suppose I only need one channel output from one DAC, why not 6 instead of 12?
3. We have one I2S from Raspberry Pi and feed to two DAC PCB, how to do it? Connect in parallel?
I am interested to build this DAC too, but have some questions and seeking for help.
1. LME49990 has been discontinued already. I am thinking of replacing the opamp to AD797 or ADA4627, any comments?
2. Why 12 x opamps are needed? Suppose I only need one channel output from one DAC, why not 6 instead of 12?
3. We have one I2S from Raspberry Pi and feed to two DAC PCB, how to do it? Connect in parallel?
Hi, it's definitely worth building it, sound quality is reallys superb!
1) Yes, that's an issue I faced when 3 of them burned :/ Managed to find original replacements. Have no idea about the options you've mentioned, maybe other members could comment on those.
2) In my case by using 12x I'm getting balanced outputs, which is what I need.
3) Yes, since it's a digital signal you just split it and feed however much devices you need.
1) Yes, that's an issue I faced when 3 of them burned :/ Managed to find original replacements. Have no idea about the options you've mentioned, maybe other members could comment on those.
2) In my case by using 12x I'm getting balanced outputs, which is what I need.
3) Yes, since it's a digital signal you just split it and feed however much devices you need.
You should follow the original project then and add the headphones amp IC, which is planned to be there anyways and also has it's tracks on PCBs.
Then you take balanced output right after I/V stage and RCA after HP amp. I'm just not sure if in this case you need to somehow disconnect HP amp when using balanced output.
Then you take balanced output right after I/V stage and RCA after HP amp. I'm just not sure if in this case you need to somehow disconnect HP amp when using balanced output.
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