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10 hours ago, Panelhead said:

What is the digital to analog converter chip? Does it offer digital attenuation. 

 

Dual PCM1794A's in monaural mode. No digital volume control at this time.

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I see in the pink box there are a couple of switching regulators and the writing says they're 'very low noise'. How low noise, are there any numbers?

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8 hours ago, opus101 said:

I see in the pink box there are a couple of switching regulators and the writing says they're 'very low noise'. How low noise, are there any numbers?

 

<50uV (20Hz to 20kHz)

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That's extremely low for a switching regulator - is there a linear post-regulator after the boost converter? Or is it just that all the switching noise isn't included in that figure because its way out of the audio band?

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2 minutes ago, opus101 said:

That's extremely low for a switching regulator - is there a linear post-regulator after the boost converter? Or is it just that all the switching noise isn't included in that figure because its way out of the audio band?

 

The noise figure that I listed is in the audio band (20Hz to 20kHz), out of band noise will be higher.

 

There is no post linear regulator, it's not really needed because the PSRR (Power Supply Rejection Ratio) of the audio circuit is better than 100dB.

 

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2 minutes ago, opus101 said:

Better than 100dB over what frequency range?

 

The DAC overall achieves a SNR of 128dB. That would not be achievable if power supplies or audio circuits were not properly designed.

 

If you are that interested about it please look at the OPA1612 datasheet.

 

Also I am starting to get used reviews of this device you can check it out here:


http://www.audiocircle.com/index.php?topic=155479.msg1677776#msg1677776

"I highly suggest that folks sign up for the tour to hear this wonderful device.

I spent a good week listening to it and came away extremely impressed with what Leo has done with this DAC hat.

For anyone that is using a Squeezebox Touch or similar unit, they should find this to be an quite an upgrade.

I did compare it to a DAC I built with AK4990 DAC chip and Salas shunt regulators DIY modular DAC 
I really could not pick one over the other. The sonic difference was completely dependent on the file being played. I feel both units are very transparent.

For under $250, the combination of a Rpi and the ApplePi DAC board is an outright bargain in today's audio world.

When it is released, I will be buying one."

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4 minutes ago, orchardaudio said:

If you are that interested about it please look at the OPA1612 datasheet.

 

I just did, I note that its PSRR is only over 100dB at low frequencies (under 1kHz). Which rather makes nonsense of a '100dB PSRR' claim when the context is switching artifacts above the audio band.

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