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ApplePi DAC -- Highest Performance Raspberry Pi DAC
ApplePi DAC -- Highest Performance Raspberry Pi DAC
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Old 10th May 2018, 09:24 AM   #51
Kris0603 is offline Kris0603  Sweden
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Orchard, i really dig your enthusiasm about your product, and as i've said before your product appears good, but kindly entertain the notion that 98.5% of the people in this particular forum know the difference about I2S and SPDIF, for instance.

Please don't take this the wrong way, i believe you are well within your forum rights to say whatever and as often as you'd like, still i can't help but think you might get more positive attention(and by extension, perhaps more interest in your product in the future) from the community as a whole if you engaged us more as a designer and maker than as an (understandably so) excited salesperson.

Your PSU btw looks nice, did you ever consider a bigger board with separate regs per dac? Can you give us any insight into your design process thinking for the PSU?

Last edited by Kris0603; 10th May 2018 at 09:30 AM.
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Old 10th May 2018, 11:24 PM   #52
orchardaudio is offline orchardaudio  United States
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Quote:
Originally Posted by Kris0603 View Post
Orchard, i really dig your enthusiasm about your product, and as i've said before your product appears good, but kindly entertain the notion that 98.5% of the people in this particular forum know the difference about I2S and SPDIF, for instance.

Please don't take this the wrong way, i believe you are well within your forum rights to say whatever and as often as you'd like, still i can't help but think you might get more positive attention(and by extension, perhaps more interest in your product in the future) from the community as a whole if you engaged us more as a designer and maker than as an (understandably so) excited salesperson.

Your PSU btw looks nice, did you ever consider a bigger board with separate regs per dac? Can you give us any insight into your design process thinking for the PSU?
See attachment for the power supply topology on the ApplePi DAC.

As you can see all of the power supplies generate little noise whether they are digital or analog. Couple that with the PSRR of the parts and noise become extremely low. That is how the DAC is able to achieve such good SNR. All power supply noise figures are measured band limited 20Hz to 20kHz.

The OPA1612 opamps have a PSRR of >70dB below 20kHz.

If proper decoupling techniques are used there is really no need use separate power supplies for each of the DAC chips. This board already achieves a cross talk of > 135dB.

In order to stay within the Raspberry Pi hat specification the board has to be the size that it is.

The second image shows FFT (A-Weighed) of the output of the DAC with 0 FS input.

The third image shows FFT (A-Weighed) of the output of the DAC with -60 dBFS input.

What else would you like to know?
Attached Images
File Type: jpg ApplePi_DAC_PS.JPG (73.0 KB, 113 views)
File Type: jpg FFT_0FS.JPG (147.7 KB, 110 views)
File Type: jpg FFT_-60dBFS.JPG (129.8 KB, 106 views)

Last edited by orchardaudio; 10th May 2018 at 11:44 PM.
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Old 11th May 2018, 02:58 AM   #53
abraxalito is offline abraxalito  United Kingdom
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Comparing the 'grass' between the two plots there does look to be significant modulation of the noise floor by the presence of the -60dB signal. Would that be attributable to the DAC chip or some other factor do you think?
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Old 11th May 2018, 10:51 AM   #54
orchardaudio is offline orchardaudio  United States
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Originally Posted by abraxalito View Post
Comparing the 'grass' between the two plots there does look to be significant modulation of the noise floor by the presence of the -60dB signal. Would that be attributable to the DAC chip or some other factor do you think?
It is an attribute of the PCM1794A, due to the way that it handles 0 input (silence).

Last edited by orchardaudio; 11th May 2018 at 10:58 AM.
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