Sound Card for XC-2

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Berni
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Sound Card for XC-2

Postby Berni » Thu Dec 17, 2009 9:43 pm

Version: 1
Status: Under development
License: Custom Licence
Download: /files/project_builds/Schem.zip

Okey so enough of PWM for audio, its time to get serious ! So i fired up Altium again and went on designing a proper sound card for the XC-2, and quite a sound card it is with its capabilitys reaching up to 192Khz at 24Bit. Still while packing a punch it remains quite tiny at 25×40mm only and half of the room are the big 3.5mm jacks. There is also a small 8 pin oscillator on the board that provides the necessary clocking to the DAC/ADC chip. The thing can be configured over SPI, I2C or hardwired setting on power up. I2C is also used to change the system clock if needed as the oscillator has a I2C port.


Note: I have no built this yet so its not verified that it works!


Bigger images on my blog post: http://thexmoschallenge.wordpress.com/2009/12/17/sound-card-pcb/


Images:
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lilltroll
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Postby lilltroll » Fri Dec 18, 2009 2:50 am

My idea for surviving the chrismas was to build a soundcard for the XC-1, with the possibillity to have a clock signal from a DSS or similair. Also I was going to do the card in Altium designer since I am evabluating it.But first I want to find possible flaws in the USB Audio 2.0 Reference Design.

Are we friends or enemies now ???
Probably not the most confused programmer anymore on the XCORE forum.
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Berni
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Postby Berni » Fri Dec 18, 2009 6:03 am

Hehe nice to hear someone else is also working on it. I mostly went on designing this cause i needed a better alternative to PWM audio
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Folknology
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Postby Folknology » Fri Dec 18, 2009 4:39 pm

Ooh I like this project it will be well handy, let us know when you have verified it.

P.S. I'm really jealous that your using Altium Designer, I might be investing in it next year.
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Berni
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Postby Berni » Fri Dec 18, 2009 4:54 pm

Theres a problem tho that i don't have the PCM3060 at hand so i hope i can get it before the holidays.
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lilltroll
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Postby lilltroll » Wed Dec 23, 2009 5:18 am

1) Have you any knowledge about the amount of output jitter when you run the DS1087 in non spread-spectrum mode?

2) Do you dare to connect the analog CODEC-output to line-out without an Output buffer? The recommended minimum impedance is 5 or 10 kOhms of the CODEC, and usually 100Ohm or less is used for driving a Line-Out. Low output impedance is nice for noise-immunity in long (non-balanced) audio cables. If the output supports the current for 16 or 32 ohm loads - headphones can be connected directly.

3) Do you dare to skip an overvoltage protection for the ADC? It might be easy to kill the Line-In !?
Probably not the most confused programmer anymore on the XCORE forum.
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Berni
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Postby Berni » Wed Dec 23, 2009 11:50 pm

Well the DS1087 may not be a very jitter free source but its good enough for this use. Newer chips aren't as sensitive to jitter as they used to be too.
And yeah i know the output is built for 5k, it should run a line out well enough( headphones ware not planned to be supported)
As for ADC protection i haven't used any as it wasn't mentioned in the datasheet.
This thing is not meant to be the new hot audiophile item! Its just a tiny simple board to get high quality audio in and out of the XC-2. Main thing here is simplicity, its a tiny board with little components. Alto i was considering putting a amplifier on the lineout to allow loads down to 16Ohm but in the end went for simplicity.(I am now thinking of putting it in and making it optional with a solder jumper)
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lilltroll
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Postby lilltroll » Sat Dec 26, 2009 1:27 am

Has the CODEC an internal low-noise LDO, or is it "only" the R1+C1||C2 filter that will reduce the noise from the USB rail, feeding the ADC and DAC in the CODEC ??
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Berni
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Postby Berni » Sat Dec 26, 2009 9:54 am

Well i think the only thing in the Vcom thats regulated inside the chip. Alto i have regulated wall wart powering the 5V rail. (XC-2 dosen't even have a usb connector). So i have much less noise on it (I know USB has a horribly noisy supply)

The main idea around this is that its a minimalist design. I wonder if its really worth it adding all those buffers and regulators on it.
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lilltroll
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Postby lilltroll » Sun Dec 27, 2009 5:08 pm

My thoughts is mostly because this is a forum site, so others (CODEC newbees) can learn/realize the good and the bad with adding more complexity to the design and problem that might arise.
Probably not the most confused programmer anymore on the XCORE forum.

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