Starting simple - my first DAC

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Well, after lurking for years this is my first post about anything I've built...

After >30yrs of building analog stuff, I decided it was time to try something digital, which also meant working with surface mount. I also wanted to try out Eagle and getting the boards made at SeeedStudio.

I started work on a simple DAC to attach to a Raspberry Pi, and my expectations for the first version were really low. I've been really surprised at how good it sounds.

It's based on a simple PCM5142 circuit, with an ADM7154 regulator. Just to get started, I used the PLL in the 5142 so I don't have to worry about a clean clock until the next version. Given that is uses the default I2C address for the 5142, it's compatible with drivers for other I2S DACs.

Like I said, it actually sounds way better than expected. It's pretty "analog" and I can't tell what impact the RPi's jittery clock is having...

I did two versions of the board, with the second one sized to fit on the Pi.

With modern tools, it's amazing how easy it was to get the boards developed and the prototype up and running.

Peter
 

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It's attached to a Raspberry Pi3 running Volumio. I have about a TB of music stored on a QNAP NAS, made up of copies of my CDs, some HDTracks downloads of 96/24 and 192/24, plus my own recordings that are either 48/24 or 96/24 (I do live sound with an amateur band and record most gigs).

PT
 
Nice. I am looking to set up a RPi or Beagle bone based DAC/ source that I can plug a hard drive straight into(.flac rips from cd).

I used to play guitar / keyboard. Arthritis limits that now. I still have my 1960 Les Paul reissue, and my JCM900 half stack! I'm Only 32, so hopefully science will fix me one day so I can play them again!
 
Interesting question. I have PurePath Studio and the PCM5142 eval board, so I could play around with the built-in miniDSP. Haven't come up with a use case yet..

It's a REALLY simple circuit. The PCM5142 implementation is straight from the datasheet, and the only thing I tweaked on the ADM5174 regulator was using a larger bypass cap to lower noise. I did use almost all C0G ceramics, since everything I have read lately suggests they are better for audio than X7s etc.

For the next version, I'm thinking of feeding the 5142 from a TI 4392 sample rate converter, with the two of them running off a very clean clock and staying at 192kHz. The fact that the 4392 has multiple inputs means I could conceivably turn this into a Pi-controlled digital pre-amp.

Peter
 

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Yes, I designed the board. This first one was deliberately simple to verify that i could make the end-to-end process work - schematic and board in Eagle, files uploaded to board house (SeedStudio), assemble the surface mount stuff and get the SW working.

Adding another ADM7154 would be easy, but I might also jump to looking at ways to improve the clock situation for the next one.

PT
 
For the next version, I'm thinking of feeding the 5142 from a TI 4392 sample rate converter, with the two of them running off a very clean clock and staying at 192kHz. The fact that the 4392 has multiple inputs means I could conceivably turn this into a Pi-controlled digital pre-amp.

Peter

With an SRC4392, you could consider using an unusual clock frequency and unusual input sample rate for the DAC, so you will have less risk that the Nth harmonic of the incoming clocks somehow produce audible difference products with the Mth harmonic of the DAC clock. The 5142 has a sigma-delta modulator on board, sigma-deltas are often particularly sensitive to interference close to odd harmonics of half their sample clock rate.

By the way, getting your first DAC to work may not be difficult, but getting it to work well is quite an achievement! Congratulations!
 
Thanks for the suggestion about the clocks! I was thinking of going with 192/24 for the 4392 to 5142 link, but you are right that if I can make it work with something different I can avoid interference/resonance issues.

Since I'm trying to proceed in small steps I will probably go with something simple first, but there's no reason not to pick something better once I have the SRC working.

Thanks again,
PT
 
If youre set on all SMD, look into MELF resistors on the output. I don't do any SMD that I don't have to, however I have heard substantial improvements using MELF over standard SMD resistors. SMD I hear are fairly poor in comparison.

Posting a pic of my pcm5122 that's about an inch square if your'e interested in how compact it can be still using through hole. 470uF caps on 3 separate power supplies using t0-92 regulators. also make sure to use low impedance caps on VNEG CAPM CAPP

WACKDAC.png
 
Yes, I designed the board. This first one was deliberately simple to verify that i could make the end-to-end process work - schematic and board in Eagle, files uploaded to board house (SeedStudio), assemble the surface mount stuff and get the SW working.

Adding another ADM7154 would be easy, but I might also jump to looking at ways to improve the clock situation for the next one.

PT

Hi, do you have a eagle lib for ADM7154? thanks
 
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