# Dreamcast Digital Audio mod?



## trumpet-205 (Feb 2, 2014)

Has anyone done this modification (tapping into digital audio signal) for Dreamcast?

http://gamesx.com/wiki/doku.php?id=av:dreamcastda

Can anyone here explain what does it mean to invert the signal?


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## FAST6191 (Feb 3, 2014)

Interesting. Is the Dreamcast DAC really worth replacing/bypassing? I would do it in a heartbeat for a lot of consoles but I have no info on the state of the DC one (a quick search says half nice TI one, no reviews of it though and I am not enough of an audio guy to truly call the graphs in the data sheet though they looked acceptable). On the other hand spdif/toslink is nice to have so I will approach it from that perspective.

Invert the signal in this case means do a logical NOT on the thing (what was 1 is now 0, what was 0 is now 1). This touches on one of the odder parts of signals here but I will leave it at the chip used in the example mod tells the chip to do sort the pre-emphasis/de-emphasis stuff (if you really want then read an article on the matter, short version is it is an audio enhancement/transmission aiding technique) by having a pin held low, the original DAC (or more accurately the internal processes of the Dreamcast feed it this) does it by having a pin held high. If you are just throwing wires around so you can add on the new chip then you are not going to have emphasis properly sorted unless you invert the Dreamcast's emphasis signal and feed that into the Cirrus chip's emphasis signal feed.

Fortunately a logical NOT/inverter is a truly simple circuit to make (you can do a basic one with two transistors if you do not fancy buying a NOT/inverter chip in and for these purposes it does not even have to be ultra fast though I would still use switching/signals grade stuff rather than power transistors or something, that said if you are buying the cirrus chip in then the same sites will sell you an inverter of more than suitable quality for about 20 cents). The only issue I see is the dreamcast thing uses TTL voltages where the example cirrus chip seems to favour slightly lower ones but reading more it seems that is not even an issue really.

Do note you have a 2007 page there, there may well be better/easier things out there now. However a quick search says the CS8406 found itself being an audio chip for automotive stuff and is still readily available.


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## trumpet-205 (Feb 3, 2014)

FAST6191 said:


> Interesting. Is the Dreamcast DAC really worth replacing/bypassing?


This is the only comparison I have seen on the net:




FAST6191 said:


> that said if you are buying the cirrus chip in then the same sites will sell you an inverter of more than suitable quality for about 20 cents).


Can you link me to an example?



FAST6191 said:


> Do note you have a 2007 page there, there may well be better/easier things out there now. However a quick search says the CS8406 found itself being an audio chip for automotive stuff and is still readily available.


From the same video, this post basically does what the 2007 page did. I did not see any mentioning on emphasis though. It seems this person simply soldered wires together. (Note: In Spanish)

http://www.elotrolado.net/wiki/Salida_de_audio_digital_SPDIF


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## Foxi4 (Feb 3, 2014)

Judging by the comparison video, there's definitely some noise reduction going on there and the output is richer, so perhaps this sort of a mod is worth a try if you're an avid audiophile.


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## FAST6191 (Feb 3, 2014)

Sorry, I really should have thrown links around then.

Step 1 is most real world suppliers are awful (I barely trust Frys or Radio Shack to sell me batteries) which means online or bust. Ebay and amazon are nice for some things (I have not checked here) but I would be half surprised if something suitable for this existed here.
This means big boy electronics suppliers, warning right now they tend to come with a hefty shipping bill unless you are buying above a certain price (if you ever see kits for this sort of thing on ebay then chances are some got a load from a proper site and bundled it), are part of a school or a big business (if you know someone with electronics hookups then have a chat).
Those that still work in the US (most of mine are UK or Europe based) are
http://www.newark.com/
http://www2.mouser.com/
http://www.digikey.com/
I was mainly looking at digikey for this.

http://www.digikey.com/product-sear...-ics/linear-audio-processing/2556582?k=cs8406 is the audio chip. You have a choice of a few different packages, the guides use SOIC and that is what I specced for the board below but TSSOP is an option. I have not looked properly to see if there would be a more suitable chip for the purpose here ( http://www.digikey.com/product-sear...=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25 if you wanted to start having a look).
http://www.digikey.com/product-detail/en/SN74LVC2GU04DBVR/296-13276-1-ND/484500 for the inverter, I misread as well and had the bulk price rather than the individual (cut tape or tube if in doubt). It will then be 60 cents.
Seriously though it is basic components to make one (even radioshack/frys will have this in sufficient quality) more than fast enough (most of those have switching times in nanoseconds, audio is in the low kilohertz and I doubt the emphasis switches on or off even close to that often, if even more than once a game)
http://www.allaboutcircuits.com/vol_4/chpt_3/2.html has more on that.
I have not looked to see if I can source one of those adapter plates. http://www.digikey.com/product-sear...t=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25 has something but it is quite pricey and the most suitable one was not in stock.

I watched the video.... I think we witnessed the start of the loudness wars as they apply to games there (though commendably they did not amplify to the point of clipping or even interpolation clipping) so I could not see much in it.
However if they left off the emphasis stuff, and it does look to be an oversight on their part, then it might be an issue for part of it. Not enough for me to call potentially a night and day difference but enough to make me pause.
Again though if you just want something you can more easily feed into an amp or something then it does not matter.


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