SCC DAC

Champion (324)

22-08-2008, 11:07

Did someone already re-built the resistor array from the konami scc cartridges?
I am working on a pcb for scc including the mmc drive of sharksym and would be nice to have the scc sounds available too. I already have scc chips on the way ...
So if some one can tell me the values to be used otherwise I have to figure it out myself (which is no big deal) but it is easier to re-use something that has already been figured out.

thx

By Erikie

Champion (324)

24-08-2008, 20:09

I made the dac from resistors like this i239.photobucket.com/albums/ff12/ErikvSon/sccdac.gif
attach r0 to snd0, r1 to snd1 etc.
I used 470 ohm for the 500 Ohm as this is not a normal value.
And the sound is the same as the original!

By ARTRAG

Enlighted (6846)

25-08-2008, 23:35

SCC has some nasty HW bug that randomly corrupts the output when you write the wave tables.
Do you emulate this effect ?

By Erikie

Champion (324)

26-08-2008, 07:57

That is a very good question. Is there any way I can test this? As I am just using the original scc chip with just a replaced resistor array I think that effect is still in place.
If you can let me know what I should do I will try this as soon as I have time to test it

By ARTRAG

Enlighted (6846)

26-08-2008, 10:22

Well the bug is still not very understood, and acts in an random way.

Start reading this tread:
http://www.msx.org/forumtopic7875p315.html

What I would do is compare the output of an emulator when playing the file "fifth_60Hz.rom"
(you find it here http://www.bluemsx.com/demos/fth01.zip with sources)
with the output of the real chip.

The same errors happens when you try this:
http://sites.google.com/site/testmsx/Home/scc-pcm-replayer
Try the sccplay.rom file both on real HW and emulator.
(the sources are in the same page)

Let me know!

By Erikie

Champion (324)

26-08-2008, 11:10

playing the rom on the real msx can be done without any specific tricks?
I can load your rom in a 512K rom and use my own built resistor network and can also put it in the mega flash scc.
I will compare those outputs for any differences.

By ARTRAG

Enlighted (6846)

26-08-2008, 12:42

Sure !! I use SCC flach rom by manuel pazos and they rock
(http://personales.mundivia.es/mpazos/flashrom/index2.html)

If you have less that 512K try my roms at the other site
(the advantage is that you can play the samples by pressing a key)

By Erikie

Champion (324)

26-08-2008, 19:56

Hmm, I am afraid the sound quality is not all too good with my resistor dac. Probably the same as with the original dac. Having trouble with my disks to boot so cannot try it with my ese-scc flash rom

By ARTRAG

Enlighted (6846)

26-08-2008, 20:49

Do you need some special size of the rom just for testing ?

By ARTRAG

Enlighted (6846)

27-08-2008, 01:52

In case I can do an ad hoc testing program of the size you need.

By Erikie

Champion (324)

27-08-2008, 09:09

Not necessary. I loaded the rom in both my ese-scc and the test print with scc chip and resistor dac. Results were both the same. Distorted sound every now and then. The emulator outputs much better quality