Great...another USB/DAC project (PCM2707+AD1896+AD1955)

freewilly · 31st May 2010, 10:11 PM

Hi this is my first post on diyaudio so go easy on me

i'm planning on implementing a USB/DAC amp for headphones. why? no apparent reason other than for kicks and I think it'd be a neat project to do.

the system level topology I've decided to go with is somewhat generic, USB->PCM2707->AD1896->AD1955->I/V conversion stage (haven't decided what opamps to use yet). The PCM2707 will output 16bit I2S format @ 44.1kHz/48kHz and the AD1896 async sample rate converter will upsample it to 24bit I2S @ 96kHz before passing it to the AD1955 DAC.

the question I have is in regards to the clocking scheme for the AD1896 (sample rate converter) and the AD1955 (DAC). The master clock frequency I plan on using is 256*fs = 24.576Mhz. Given this, what would be your 2 cents in the clocking topology for the AD1896 and AD1955?

I've seen on the AD1896 EVB, they have used an XO to clock the AD1896. And at the MCLK output of the AD1896 (MCLK-O), this clock signal drives the MCLK for the AD1955, after being buffered. Is this recommended? what about using a TCXO instead?

Thanks!

chaparK · 1st June 2010, 12:58 AM

Sound like a cool project!

Why are you using a sample rate converter?

Cheers,

chaparK

wwenze · 1st June 2010, 01:09 AM

If possible find TE7022L - 24/96 through USB.

freewilly · 3rd June 2010, 08:24 PM

chaparK
To be honest, I am fairly new to the audio scene myself. That being said, I believe it helps in jitter reduction. I'm trying to read up as much material about it as possible, but I've decided to populate it for the time being and test it out myself.

wwenze
I'll take a look at the TE7022L. I'll have to first see how readily available this part is, especially for a hobbyist like me

stokessd · 3rd June 2010, 09:45 PM

I'd add the ASRC to the design, you can always not populate it, and jumper the four signal lines across the pins. Just make sure that whatever pins on the DAC need to be set for sample rate have external jumpers etc. That way you can have your cake and eat it too.

According to someone smarter than I, ASRC can be very useful:

Asynchronous Sample Rate Conversion

Sheldon

freewilly · 4th June 2010, 06:56 PM

Cool thanks Sheldon! i'll read into that thread.

I guess I'll take a step back from my initial question and ask, what TCXO do people recommend I use to clock the AD1896 and AD1955?

31st May 2010, 10:11 PM	#1
freewilly diyAudio Member Join Date: May 2010 Location: chicago, il	Great...another USB/DAC project (PCM2707+AD1896+AD1955) Hi this is my first post on diyaudio so go easy on me i'm planning on implementing a USB/DAC amp for headphones. why? no apparent reason other than for kicks and I think it'd be a neat project to do. the system level topology I've decided to go with is somewhat generic, USB->PCM2707->AD1896->AD1955->I/V conversion stage (haven't decided what opamps to use yet). The PCM2707 will output 16bit I2S format @ 44.1kHz/48kHz and the AD1896 async sample rate converter will upsample it to 24bit I2S @ 96kHz before passing it to the AD1955 DAC. the question I have is in regards to the clocking scheme for the AD1896 (sample rate converter) and the AD1955 (DAC). The master clock frequency I plan on using is 256*fs = 24.576Mhz. Given this, what would be your 2 cents in the clocking topology for the AD1896 and AD1955? I've seen on the AD1896 EVB, they have used an XO to clock the AD1896. And at the MCLK output of the AD1896 (MCLK-O), this clock signal drives the MCLK for the AD1955, after being buffered. Is this recommended? what about using a TCXO instead? Thanks!

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1st June 2010, 12:58 AM	#2
chaparK diyAudio Member Join Date: Apr 2010 Location: Sydney	Sound like a cool project! Why are you using a sample rate converter? Cheers, chaparK

1st June 2010, 01:09 AM	#3
wwenze diyAudio Member Join Date: Mar 2008	If possible find TE7022L - 24/96 through USB.

3rd June 2010, 08:24 PM	#4
freewilly diyAudio Member Join Date: May 2010 Location: chicago, il	chaparK To be honest, I am fairly new to the audio scene myself. That being said, I believe it helps in jitter reduction. I'm trying to read up as much material about it as possible, but I've decided to populate it for the time being and test it out myself. wwenze I'll take a look at the TE7022L. I'll have to first see how readily available this part is, especially for a hobbyist like me

3rd June 2010, 09:45 PM	#5
stokessd diyAudio Member Join Date: Nov 2002 Location: Fort Wayne, IN	I'd add the ASRC to the design, you can always not populate it, and jumper the four signal lines across the pins. Just make sure that whatever pins on the DAC need to be set for sample rate have external jumpers etc. That way you can have your cake and eat it too. According to someone smarter than I, ASRC can be very useful: Asynchronous Sample Rate Conversion Sheldon

4th June 2010, 06:56 PM	#6
freewilly diyAudio Member Join Date: May 2010 Location: chicago, il	Cool thanks Sheldon! i'll read into that thread. I guess I'll take a step back from my initial question and ask, what TCXO do people recommend I use to clock the AD1896 and AD1955?

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