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Starting simple - my first DAC
Starting simple - my first DAC
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Old 21st October 2017, 04:58 AM   #1
commuteman is offline commuteman  United States
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Join Date: Jul 2004
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Default Starting simple - my first DAC

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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File Type: jpg RPiDacv1.jpg (752.3 KB, 350 views)
File Type: jpg SeedBoards.jpg (804.5 KB, 341 views)
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Old 21st October 2017, 05:38 AM   #2
BJosephs is online now BJosephs  United States
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Very nice! It works, looks good, and you like it. Sounds like a success!
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Old 21st October 2017, 06:20 AM   #3
commuteman is offline commuteman  United States
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Thanks. Given that it was a first test, I was shooting for "it works". Anything beyond that was a pleasant surprise...

PT
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Old 21st October 2017, 06:29 AM   #4
helitim is offline helitim  Canada
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Cool project! What are you using for a music source?
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Old 21st October 2017, 06:56 AM   #5
commuteman is offline commuteman  United States
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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
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Old 21st October 2017, 07:57 AM   #6
helitim is offline helitim  Canada
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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!
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Old 23rd October 2017, 10:29 PM   #7
PaulFrost is offline PaulFrost
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Nice! Looks really clean. Are you going to play with the DSP too?
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Old 24th October 2017, 10:06 PM   #8
commuteman is offline commuteman  United States
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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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Old 24th October 2017, 10:51 PM   #9
PaulFrost is offline PaulFrost
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A project in the future could be to configure the GPIO pins as an I2S output from the DSP and connect them to a second PCM device (PCM5102A perhaps) to create a 2.2 type setup where the DSP can work as a digital cross over or LPF. Might be fun.
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Old 24th October 2017, 11:01 PM   #10
commuteman is offline commuteman  United States
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I thought about that, and I think the Allo Piano 2.1 DAC was supposed to do something like that - use the miniDSP to create a separate sub output.

PT
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