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av:dreamcastda [2007/08/09 13:46] (current)
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 +==== Adding Digital Audio to the Sega Dreamcast ====
  
 +And on the heels of the Saturn digital audio mod here's one for the dreamcast.
 +
 +The dreamcast generates digital audio internally and then passes it to a digital analog converter chip. As it uses an off the shelf d/a converter (PCM1725U) it's possible to interface the digital audio signals to an S/PDIF transmitter IC that will transform the digital audio into a form your amplifier will understand. ​
 +
 +Here are the hookups for the Cirrus CS8406 chip I used here.
 +
 +{{av:​dreamcast_da_chip.gif}} {{av:​pcm1725.gif}}
 +
 +
 +^  Signal ​ ^  CS8406 ​ ^  PCM1725U ​ ^
 +|  EMPH: emphasis - See Note!! |  3  |  12  |
 +|  ILRCK: Word Clock  |  12  |  1  |
 +|  ISCLK: Bit Clock  |  13  |  3  |
 +|  SDIN: Audio Data  |  14  |  2  |
 +|  OMCK: Master Clock  |  21  |  14  |   
 +|  GND  |    |  7  |
 +|  +5v  |    |  8  |
 +|  TXP: S/Pdif output ​ |  26  |    |
 +
 +You can hook up a toslink transmitter directly or wire up a coax connector with the same circuit as in the SNES mod.
 +
 +{{av:​coaxial.gif}}
 +
 +
 +
 +===Note===
 +
 +I looked at the data sheets again. The EMPH line on the cirrus chip is high for no pre-emphasis. Pin 12 on the PCM1725U is high for de-emphasis active. Therefore the signal should be inverted. ​
 +
 +=== Construction ===
 +
 +My first mod using the CS8406 was adding digital audio to the saturn. I wired everything directly to the chip. It worked but was a rather nerve wracking experience.
 +
 +{{av:​dreamcastda_chip.jpg}}
 +
 +This time I used a soic to dip adaptor board and the soldering was a lot easier. The board adds a bit to the cost but it's worth it. You can't see it in the pic, but there is a small capacitor between +5V and Ground. The chip works without it but it seemed a good idea.
 +
 +A few notes on installation:​
 +I soldered the +5v and GND leads to CF302 rather than the chip as access is a bit easier. When placing the toslink optical transmitter or RCA jack make sure you do a dry run and put the board in the case with the top and bottom rf shields in place. For instance I put the RCA jack around the corner from the expansion port and found that I needed to put the top shield in place before I soldered the orange TXP wire to the RCA jack. 
 +
 +
 +== Where to find the parts ==
 +
 +CS8406 soic package: [[http://​www.newark.com/​jsp/​Semiconductors+&​+Prototyping/​Interface+&​+I/​O+Controller+ICs/​CIRRUS+LOGIC/​CS8406-CSZ/​displayProduct.jsp?​sku=88H6505| Newark]]
 +
 +SOIC to DIP adaptor board:
 +[[http://​nkcelectronics.com/​soic-to-dip-adapter-28p.html|NKCElectronics]] ​
 
 av/dreamcastda.txt ยท Last modified: 2007/08/09 13:46 (external edit)
 
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