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Dual PCM1794A DAC Module - PecanPi
Dual PCM1794A DAC Module - PecanPi
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Old 24th January 2020, 10:24 PM   #1
orchardaudio is offline orchardaudio  United States
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Default Dual PCM1794A DAC Module - PecanPi

Hello,

I am in the process of designing a PecanPi DAC module that I already have a customer for. They are purchasing 100 of them.

I am putting this here to see if anybody else would like to join in to purchase these modules. Each module will be about $200 each. I will have final pricing in the next two weeks or so. The price will be lower with more buyers.

The modules will feature dual PCM1794A DACs in monaural mode and have specifications identical to my company's PecanPi DAC.

The module will have:
  • Balanced and single-ended outputs.
  • The input power supplies will be +/-12V (analog) and 3.3V (digital)
  • The size of the module will be 74 by 64mm as per the attached drawing.
  • The input signals will be I2S at 3.3V and support up to 24/192.
  • The modules will use my proprietary dual differential output stages with OPA1612 op-amps.
  • Complete reclocking with Crystek femtosecond jitter oscillator
Attached Images
File Type: jpg Module.JPG (66.2 KB, 167 views)
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Old 25th January 2020, 02:02 PM   #2
orchardaudio is offline orchardaudio  United States
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I can also sell just the bare boards and provide a BOM if this is of interest here.
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Old 26th January 2020, 01:12 PM   #3
hidjedewitje is offline hidjedewitje  Netherlands
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I think people will be more interested if you post measurements or some more documentation about the project.
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Old 26th January 2020, 01:19 PM   #4
orchardaudio is offline orchardaudio  United States
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Quote:
Originally Posted by hidjedewitje View Post
I think people will be more interested if you post measurements or some more documentation about the project.
Thank you for your suggestion, measurements will be added shortly.
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Old 26th January 2020, 01:22 PM   #5
orchardaudio is offline orchardaudio  United States
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As per previous post... measurements/test results attached.

Half of the images are for single-ended output (2.5V at 0dBFS) and half the images are for the balanced output (5V at 0dBFS).

These measurements are from my PecanPi DAC, I don't see any reason the module will be any different as it uses the same exact parts and layout.

Implementation
DAC chips:
  • Dual flagship Burr-Brown PCM1794As in monaural mode

Reclocking
  • Crystek CCHD-575 oscillator -- ultra-low clock jitter of 82fSec
  • SRC4193 for reclocking

Output stage: True balanced dual different output stages
  • Uses OPA1612s
  • 0.1% low noise Panasonic resistors
  • 1% high-quality COG capacitors
  • Proprietary filtering topology

Ultra-low noise linear power supplies:
  • TPS7A4700 (4.17uV noise) for positive op-amp power supply
  • TPS7A3301 (16uV noise) for negative op-amp power supply
  • TPS7A4901 (15.4uV noise) for DAC Chips

Let me know if you have any additional questions.
Attached Images
File Type: jpg Dashboard (RCA).JPG (237.8 KB, 122 views)
File Type: jpg Dashboard (XLR).JPG (245.6 KB, 117 views)
File Type: jpg Dynamic Range (RCA).JPG (85.9 KB, 115 views)
File Type: jpg Dynamic Range (XLR).JPG (85.8 KB, 112 views)
File Type: jpg Jitter (RCA).JPG (115.0 KB, 29 views)
File Type: jpg Jitter (XLR).JPG (108.9 KB, 29 views)
File Type: jpg THD+N vs Level (RCA).JPG (97.2 KB, 25 views)
File Type: jpg THD+N vs Level (XLR).JPG (95.1 KB, 17 views)
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Last edited by orchardaudio; 26th January 2020 at 01:33 PM.
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Old 1st February 2020, 01:49 PM   #6
orchardaudio is offline orchardaudio  United States
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The DAC modules fully assembled will be $185 each.
The bare boards will be $25 each.
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Old 2nd February 2020, 01:00 AM   #7
fab is offline fab  Canada
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Dual PCM1794A DAC Module - PecanPi
Hi

Interesting .

Have you also considered other opamps for output stage. I know well the opa1612 in the output stage of DAC and while it is good I prefer the sound of AD4898-2 for that application. At least it is my preference when associated with an AK-449x DAC. The AD opamp is more expensive though than the OPA1612....

Additionally the OPA1642 sounds fine to me with the PCM1793 chip. Another jfet good sounding opamp in this application to consider is the AD8620.

From my humble experience the output stage opamp of the DAC can make a noticeable sound difference

Fab
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Last edited by fab; 2nd February 2020 at 01:11 AM.
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Old 2nd February 2020, 02:41 AM   #8
orchardaudio is offline orchardaudio  United States
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Quote:
Originally Posted by fab View Post
Hi

Interesting .

Have you also considered other opamps for output stage. I know well the opa1612 in the output stage of DAC and while it is good I prefer the sound of AD4898-2 for that application. At least it is my preference when associated with an AK-449x DAC. The AD opamp is more expensive though than the OPA1612....

Additionally the OPA1642 sounds fine to me with the PCM1793 chip. Another jfet good sounding opamp in this application to consider is the AD8620.

From my humble experience the output stage opamp of the DAC can make a noticeable sound difference

Fab
For this particular build, the customer (100 pieces) has tested PecanPi with the OPA1612 and was very happy, so the boards will be made with these particular op-amps.

Now if you get the bare boards, you are welcome to use any opamp that is pin-compatible with 1612 for the final output stage.
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Old 2nd February 2020, 04:11 PM   #9
fab is offline fab  Canada
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Dual PCM1794A DAC Module - PecanPi
Thanks for your response. Unfortunately I do not have the skills to mount all smd parts on a bare board...

I would encourage you though to try some of the opamps I have listed maybe in the future or for yourself...

Fab
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