Capcom CPS-1 "Stereo" Sound from CN5 Connector

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Capcom CPS-1 "Stereo" Sound from CN5 Connector

Some of you may enjoy this. I saw an old post on Neo Geo forums saying "just connect via CN5 and you get stereo sound from your CPS1 A board", not much more information. I saw a couple other posts across other forums (including here) ranging from "I'm working on this thing, which I saw at Neo Geo forums" but no follow-up confirming success or failure, and another thread "I made this adapter for CN5 output but the sound is garbage".

Well, I made an adapter for CN5, and sure enough, the sound was garbage. Right channel louder than left, but overall audibility very low with an external amp turned all the way up.

So, I stared at the CPS1 motherboard schematic for a while, and it sure looks like the intent is there to provide 2 channel sound via CN5. Well, the key is removing VR1. Alternatively, you may be able to put a simple on/off switch in line ahead of VR1. I haven't tested that yet, though.

1) Make an adapter from a PC case fan plug spliced to a stereo 3.5mm connector (or other suitable stereo connector)



2) Connect adapter to game board and to an amp. I hooked it up to my Q-sound amp, and used this Radio Shack volume control adapter, with 3.5mm in and 3.5mm out. If you are hooking up to an amp that has volume control on it, then you obviously don't need something like this.


3) Enjoy "stereo" sound from CPS1 games that support it.

Note that once VR1 is removed, you will not get audio through the JAMMA connector. So, it's either JAMMA mono or CN5 "stereo", but not both simultaneously. If someone can stare at the CPS1 A board schematic longer than I did and see a way to have both going simultaneously, please post.



I went ahead and captured some direct feed of GNG and SF2 HF. Below is the supported game list. GNG is not on there, so it was a good test.

My assessment: GNG has slightly lower audio on the right channel. Possibly non-supported games are actually at a disadvantage using CN5 output. SF2 HF splits the FM sounds across the channels – instruments are on the left channel, percussion is on the right. Non-FM sounds play through both channels. The splitting is most noticeable during Ken's ending, when the wedding song starts playing. Also, possibly richer bass tones for SF2 HF.

GNG direct feed capture: https://youtu.be/ojk19Lo-oKg

SF2 HF direct feed capture: https://youtu.be/1vMTSlAtNg4

Supported game list. I thought I saw a longer list just a couple days ago on a different forum, but couldn't find it again. If somebody finds it, please copy and paste.

http://www.neo-geo.com/forums/showt...m-CPS-1-boards&p=133483&viewfull=1#post133483

1941
Adventure Quiz Capcom World
Adventure Quiz Capcom World 2
Street Fighter II (also CE, etc.)
Strider
UN Squadron
Captain Commando

Enjoy!
 
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Nice post! I had tried that connector once to get stereo sound after reading I think a Neo Geo forum and got similar results with the unbalanced audio.

It's nice to see where you've taken it and I may try this method.
 
Okay, so it's not really "true" stereo output then on SF2. E.g. if the action is on the left hand side of the screen, the left speaker would be more active and vice-versa.

Seems like a faux-stereo where some instruments are on one channel, some are on another, and the game sound effects are played through both?
 
Okay, so it's not really "true" stereo output then on SF2. E.g. if the action is on the left hand side of the screen, the left speaker would be more active and vice-versa.

Seems like a faux-stereo where some instruments are on one channel, some are on another, and the game sound effects are played through both?
Yes, essentially. That's why I also used "air quotes". [emoji14] it's a minor upgrade to jamma mono. Kinda cool.
 
Thanks for sharing. I was all hyped about the possibility of this when I first got my Big Blue but never figured it out.
 
This isn't stereo, it's just two different points from the line-level mixing circuits between the OKI6295 and the YM3014/YM3012 DAC. Game sound effects for SF come primarily from the '6295.
 
This isn't stereo, it's just two different points from the line-level mixing circuits between the OKI6295 and the YM3014/YM3012 DAC. Game sound effects for SF come primarily from the '6295.
Which is why I us3d air quotes aka, used the term "stereo" loosely. It is certainly an attempt by capcom to provide an improved audio experience in lieu of jamma mono, although interesting that there doesn't seem to be much documentation about it, at least none that I've found from archived documents from the period. Also interesting to note that the sf2ce arcade manual says sf2ce offers stereo sound, but only gives the jamma mono pinout.

So, what would be the more accurate description of it if stereo isn't the correct term?
 
Which is why I us3d air quotes aka, used the term "stereo" loosely. It is certainly an attempt by capcom to provide an improved audio experience in lieu of jamma mono, although interesting that there doesn't seem to be much documentation about it, at least none that I've found from archived documents from the period. Also interesting to note that the sf2ce arcade manual says sf2ce offers stereo sound, but only gives the jamma mono pinout.

So, what would be the more accurate description of it if stereo isn't the correct term?


I'm pretty sure this output is only there for the sake of tests, or some esoteric cabinet configuration that includes its own amplifier. The only reason I can think of for this to be there other than engineering testing is if they wanted to use different speakers for sound effects and music, but assigning them left/right channels wouldn't be appropriate.

Any game using sample playback is "supported", but calling it that isn't really the right term...
 
I thought of that too - it is a convenient test point in the event of loss of audio (which I have on 2 boards on my bench currently :/ ) to determine if the problem is in the region of the amp or in the region of the 6295/ym3012/z80/etc. But why split the FM sounds just for the sake of a test point connector? And if it were a test point which is really (presumably) there for A board troubleshooting, why do some games offer the split FM effects and some games dont?
 
Zero games offer split FM effects. The only games that wouldn't seem to have any split are games that don't use the OKI for sound effects, like Daimakaimura. Again, both points contain both sounds, just the OKI is overwhelmingly loud on the other.

It is not unusual for game boards to have "unnecessary" test points and IO ports on them from the factory. Calling this header stereo is misleading, however.
 
I'm not clear where the misleading occurred. I felt I adequately described in the OP what is occuring with the audio, to the best of my ability to describe it, from my observations. The concept was then further clarified through additional discussion including your technical explanation, which was good information.

Maybe the title promised more than the thread delivered, and if that's the case, I apologize. No malicious intent here. Just sharing something I thought was interesting, but maybe I'm the only one that does, and that's okay too. :bigok:
 
So is the pseudo-stereo coming from the CN5 connector a pre-amp line level signal? So if VR1 is removed I can go straight from CN5 to an external amp with no danger of blowing anything? If so, that's great news for what I'm building...
 
I had this on my to-do list forever (since you originally posted). I recently agreed
to sell one of my big blues to a local guy who is into Hyperfighting tournaments. Of course he wanted to drop that into the cab that was factory wired for CPS2 so I tried this mod and it was the perfect solution! Thanks for the write-up.
 

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