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Old 14th January 2013, 06:44 AM   #1
JanErik is offline JanErik  Finland
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Default DAC chip for PCM2707

Which I2S DAC would you recommend for this? I have found this:
Audio Converter - Audio DAC - PCM1792A - TI.com
and a project made with this: AD1955 datasheet and product info | High Performance, Multibit Sigma-Delta DAC with SACD Playback | Audio D/A Converters | Analog Devices
but I am unsure how it is to be set up with the clock generator...

TI recommends this: Audio - Audio Clock - PLL1700 - TI.com

How do I get started on this?
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Old 15th January 2013, 09:51 PM   #2
Rochey is offline Rochey  United States
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JanErik,

PCM2707 has a system clock output as well. You can hook this directly to your PCM1792A.

An External Crystal (and 2x caps) can be hooked up to the PCM2707 for the 12MHz clock.

I don't see where you'd need the PLL17xx device. Can you let me into your thought process?

Thanks again

Dafydd Roche (TI Audio Converter Systems Engineer).
P.S. For further reference, you may want to read some of the threads over at:
Data Converters - TI E2E Community
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Old 16th January 2013, 06:52 AM   #3
JanErik is offline JanErik  Finland
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As I understand it, the PCM1792A needs higher clock frequencies for its oversampling.

Yeah, I have already built a USB DAC with PCM2705 so I have its clock working.
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Old 16th January 2013, 09:35 AM   #4
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What about using a high precision XO for the System clock of the PCM1792 (according to the table on page 15 of the datasheet) and devide it down 2 or 4 times according to the need of the 2707 using high speed D-Flip-Flops.
Did this for the combination of ES9023 and WM8804 (49,152 MHz and 12,288 MHz).

Last edited by curryman; 16th January 2013 at 09:41 AM.
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Old 16th January 2013, 09:38 AM   #5
JanErik is offline JanErik  Finland
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As I understand it, the 1792 clock frequency is dependent on the sampling frequency of the input data... which can vary depending on material?
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Old 16th January 2013, 12:57 PM   #6
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Sorry, have been a bit too fast My thoughts might not apply to your setup.

According to the datasheet the PCM2707 supports 32, 44.1 and 48 kHz samplerate with SYSCK = 256Fs available at the corresponding I2S header pin (FUNC2, Pin18). You could use this as system clock for 1792. However the jitter related performance will not be very good due to 2707 using adaptive isochronous USB transfer. Could be improved using SPDIF and an aditional SPDIF receiver chip (e.g. WM8804) with reclocking, though not sure if its worth the effort.

PCM2707 quite easy to implement, but wouldn't it be better to go for other solutions like XMOS (e.g. used on USBstreamer) to get the most out of the 1792? If you are not fixed to complete DIY you could use just one of the available USB to I2S interfaces like that shown in the link. Just an idea...

Last edited by curryman; 16th January 2013 at 01:14 PM.
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Old 16th January 2013, 07:35 PM   #7
JanErik is offline JanErik  Finland
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Oops, I didnt realize that it already gives the necessary clock!

I do think the USB is just fine, the PCM2705 already sounds good but I would like to use a more high-end DAC. Likely also powered over USB, despite what people may say :P

An SPDIF DAC is a separate project I am thinking of.

But I am aiming to do it totally DIY, this is hobby and there is no fun otherwise.
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Old 17th January 2013, 03:10 PM   #8
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Quote:
Originally Posted by JanErik View Post
Which I2S DAC would you recommend for this?
Best-buy solution is to use it with TDA1543. I am using it with AD1865 (non-os).
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Old 17th January 2013, 03:41 PM   #9
JanErik is offline JanErik  Finland
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It seems to be quite old chip...? And I cant find it in any store nor to be sampled.
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Old 17th January 2013, 04:15 PM   #10
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Quote:
Originally Posted by JanErik View Post
It seems to be quite old chip...? And I cant find it in any store nor to be sampled.
TDA1543 or AD1865? Or booth? Just kidding
My point is... best way is to use PCM2707 in non-os configuration with some good-sounding DAC chip with I2S input (for example TDA1543) without any glue logic. Anyway, TI PCM USB chips properly implemented have also good sound by themselves without using of external DAC.
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