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Sound Card for XC-2

by Berni

  • Status: Under development
  • Downloads: 158
  • Licence: Please contact author for terms
  • Last updated: 17/Dec/2009 at 08:44 PM
  • Wiki entry: View project wiki entry

Version 1

Size: 66.39kb

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Project Overview

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/

Verified to run on

Images and diagrams

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Comments / Updates

did you ever print this board and try it?

i would go for ballanced XLR or TRS really ..
may be optical adat would be even easier? ..hm

i will try to figure something out as soon as i get my first kit!

digital i/o is better for me to use, so i can finally deploy the digital outputs and inputs of my soundcard!

Yes that is correct. Id use 1bit ports on all of them but one connector only has 4.So i put I2C on a 4 bit port cause its not going to be used for other than setting up the card to a certain mode and only writes to the I2C are needed.

Just checking the expected port usage :
1 * 4 bit port for the both the I2C and Reset and MS/ADR
4 * 1 bit ports for the SPI ?
Is this correct?
regards
Al

Well i could try to make a high quality version of the board, there is still some free room on it.

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.

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.

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 ??

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)

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 !?

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