After my experience building and listening to this DAC, I have made some modifications. I included the missing trace, moved some pads that were confusingly symmetrical, and redrawn the transformer at the correct size.
Those are the changes intended for the poor guy building the circuit. The changes for the poor guy <em>listening</em> to the circuit are the separate ground planes. There is one ground plane for the connector and transformer primary, and another "drawbridge" plane for the rest of the circuits. This should cut down on the slight hash imposed on the analog outputs. The builder has the option to power the digital and analog sides from completely separate supplies all the way back to the power transformer.
Those are the changes intended for the poor guy building the circuit. The changes for the poor guy <em>listening</em> to the circuit are the separate ground planes. There is one ground plane for the connector and transformer primary, and another "drawbridge" plane for the rest of the circuits. This should cut down on the slight hash imposed on the analog outputs. The builder has the option to power the digital and analog sides from completely separate supplies all the way back to the power transformer.
Attachments
Manufacturing information
By demand from two members of this forum, I have prepared the manufacturing information for this board. The attached zip file contains Gerber files for the top, bottom, and both sides' solder masks as well as the Excellon drill file. The zip is suitable for sending to PCB Express, and of course the solder masks can be omitted to save cost.
Cheers,
jwb
By demand from two members of this forum, I have prepared the manufacturing information for this board. The attached zip file contains Gerber files for the top, bottom, and both sides' solder masks as well as the Excellon drill file. The zip is suitable for sending to PCB Express, and of course the solder masks can be omitted to save cost.
Cheers,
jwb
In case you need the Bill of Materials, it is here:
http://atari.saturn5.com/~jwb/43122-bom.html
Also the schematic is here:
http://atari.saturn5.com/~jwb/43122.png
http://atari.saturn5.com/~jwb/43122-bom.html
Also the schematic is here:
http://atari.saturn5.com/~jwb/43122.png
. I thought all high end DACs had current output. It's been awhile since I looked at the CS43122 datasheet!
Newbie questions
I've never built a DAC before, and I'm thinking of trying this one. But I have some newbie questions:
How do I connect the power supply to this? It says different supplies can be used for the digital and analog portions, but I'm not sure where the digital ends and the analog begins. Also, how much filtering does the power supply need (and is it the same for both the digital and analog parts)? Is a 10V regulated wall-wart sufficient? Additionally, how do I connect the audio outputs and digital input? How can I have multiple input connectors (i.e. coax, optical)? How do I connect SPDIF?
I've never built a DAC before, and I'm thinking of trying this one. But I have some newbie questions:
How do I connect the power supply to this? It says different supplies can be used for the digital and analog portions, but I'm not sure where the digital ends and the analog begins. Also, how much filtering does the power supply need (and is it the same for both the digital and analog parts)? Is a 10V regulated wall-wart sufficient? Additionally, how do I connect the audio outputs and digital input? How can I have multiple input connectors (i.e. coax, optical)? How do I connect SPDIF?
There is a Molex connector at the top of the image. This is the +/gnd/- supply for the analog section. There are two vias on the left of the image, these are the +/gnd supply for the digital section. The two vias at the bottom of the board are the +/gnd supply for the clock and input filter. There may be some advantage to separating this from the digital supply.
If you want to use a wall wart, you will need one with +10V, -10V, and GND. Also you will need a <b>regulated</b> wall wart. Otherwise you will get 60Hz noise on the analog output.
The analog outputs are the four vias in a vertical row on the upper right of the image. There are positive and inverted outputs for left and right. I forget which is which; check the datasheet for the CS43122. The outputs need to be AC-coupled using 4.7µF or bigger film capacitors, and tied to ground with some value of resistor.
If you don't want balanced output, obviously you can simply leave the inverted outputs unattached.
The input connector in this design is a 75Ω BNC. If you want optical you would need to modify the design. If you want both optical and coaxial, you will need some extra control circuitry.
Cheers,
jwb
If you want to use a wall wart, you will need one with +10V, -10V, and GND. Also you will need a <b>regulated</b> wall wart. Otherwise you will get 60Hz noise on the analog output.
The analog outputs are the four vias in a vertical row on the upper right of the image. There are positive and inverted outputs for left and right. I forget which is which; check the datasheet for the CS43122. The outputs need to be AC-coupled using 4.7µF or bigger film capacitors, and tied to ground with some value of resistor.
If you don't want balanced output, obviously you can simply leave the inverted outputs unattached.
The input connector in this design is a 75Ω BNC. If you want optical you would need to modify the design. If you want both optical and coaxial, you will need some extra control circuitry.
Cheers,
jwb
OK, I opened the CAD files in EAGLE, but the bottom layer (blue), instead of being filled in like in your picture, it's just a thick outline. Is this how it's supposed to be? (I needed to open it so I can trim a couple of millimeters off the board size so I can get cheaper deal with the PCB maker).
About the power supply: I don't know much about designing power supplies, but if I start with a single wall wart, what would be the total current that the wall wart should be able to supply? Can I have a design where I have a say 24 V wall wart and use two regulators to get the +10 V and -10 V? And what would be appropriate filtering for each section (digital and analog; and should the separation and filtering for each section be before or after the regulators)?
Thanks to diyaudio.com user rpell, who built this circuit and pointed out a few bugs. There was a mistake in the <a href="http://atari.saturn5.com/~jwb/43122.png">schematic</a> listing a 4.7KΩ resistor which should be 47K. Also the <a href="http://atari.saturn5.com/~jwb/43122-bom.html">bill of materials</a> has been updated to include R3 and R12 on the 5.5V regulator and a change from ZTX869 to cheaper but still good ZTX450 for the constant current sources. A bug in the layout of the ground plane under the input connector was also fixed.
The question came up of what to do with the ground point near the input connector. This via should be used to attach this ground to the chassis near the input. It should not be connected to the main system ground point.
Here are the updated data for anyone who wants to build this. Besides the fixes, I made one small change: under the clock generator are five pads for a Hirose PCB-mount vertical MMCX connector. You could use this to feed in your favorite clock signal instead of using the on-board clock chip. Could be some good room to experiment there.
Have fun,
jwb
The question came up of what to do with the ground point near the input connector. This via should be used to attach this ground to the chassis near the input. It should not be connected to the main system ground point.
Here are the updated data for anyone who wants to build this. Besides the fixes, I made one small change: under the clock generator are five pads for a Hirose PCB-mount vertical MMCX connector. You could use this to feed in your favorite clock signal instead of using the on-board clock chip. Could be some good room to experiment there.
Have fun,
jwb
This is the dac I want to build, but before sending the boards to be manufactured I would like to here some comments on:
* The groundplanes
* The oscillator clock trace and decoupling
* The spdif routing
All smd is mouted on the bottom of the board and all hole-trough mounted is on the toplayer, The outputstage is based on LL1527 transformers.
And thanks to JWB for sharing the Cad files so I really can mess things up ;-)
/ Micke
* The groundplanes
* The oscillator clock trace and decoupling
* The spdif routing
All smd is mouted on the bottom of the board and all hole-trough mounted is on the toplayer, The outputstage is based on LL1527 transformers.
And thanks to JWB for sharing the Cad files so I really can mess things up ;-)
/ Micke
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