The Omega Machine Part 3 (Xbox to Jamma)

bya Phil at 4:30 AM

Time to post again. This time Xbox to Jamma audio. We learned how to hook up video to our Jamma cab from the Xbox, but now we need a cheap way to do Audio.

XBox to Jamma Audio

There’s a cuple ways to do this, but I always strive for the easiest and cheapest mix.

Let’s take a look at where we left off. I made a better diagram of how we hooked up the video.

Now we need a cheap easy way to hook up the audio. Well one might think at first, just hook up the audio pins from the Xbox a/v cord to the Jamma board. This of course, is wrong. The audio from the Xbox is not amplified and a typical Jamma cab has no audio amplifier.

Ya could build a small audio amplifier circuit, but this is too much of a pain in the ass I think. I did it the easy way. Go down to your cheap computer store or thrift store, and pick up some old computer speakers with a built in amplifier (ie. with Volume Control).

Once ya got the speakers it’s time to do some wire splicing. You should have an “audio in” plug that normally hooks up to a PC. This must be spliced and hooked up to the Xbox cable pins.

It’s stereo so you’ll have a wire for the right speaker a wire for the left and a ground. Right is usually red, left is white, and ground is black. Just wire the right and the left together and make it mono. We will call the left and right wired together “audio+”. Your Jamma cab is probably mono. The ground will be called “audio-“.

So wire your audio+ to pin 14 and your audio- to pin 15 on the Xbox a/v cable. Oh by the way you may have noticed I’ve placed jumper wires between pins 1 and 14, and 2 and 15. Pin one is the right audio+ and pin 14 is the left audio+. Pin 2 is the right audio- and pin 15 is the left audio-. So the jumper pins just make the Xbox cable mono.

Next ya cut off the speaker without the audio amp built into it. We won’t need it.

Open the speaker with the audio amp. You’ll see two wires going to the cone speaker itself. One will probably be red or white and the other will probably be black. Cut these wires and remove the speaker. The black is usually the audio- and the red or white is usually the audio+. Solder the audio- to the speaker- pin on the Jamma board and the audio+ to the speaker+ pin on the Jamma board.

Lets take a look at the hookup with the audio and video hookup.

Now ya should have audio and video on your Jamma cab. Controls should be easy to hook up. But if you need help I’ll probably post later and show ya a cheap easy way to make some arcade controls for our Xbox to Jamma cab.

If your curious as to the restult… Take a look…

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The Omega Machine Part 2

bya Phil at 4:35 AM

Modded Double Dragon Cabinet

Sorry about the long delay. I’m in China for a year and have been quite busy. Here’s the next step though for our Xbox to Jamma conversion.

Xbox to Jamma (Video)

Anyway continuing from the previous post, we now we have Red, Green, Blue, and Composite Signal from our Xbox cable. Composite Signal is a mix of the video signal with the video sync. Our Arcade monitor can only understand the RGB and video(composite) sync. So that extra video signal becomes a problem and we have to filter it out. Luckily this is easy to do.

I worked on a Jamma cab and I wanted to keep it stock in case my bro ever wants to do something to it later. So I bought a Jamma Fingerboard offline for about 4 bucks, and a LM1881N chip to split up the sync and the signal.

It’s super easy…
I know it looks crappy. Click on the image to make it big.

Xbox to Jamma

Xbox to Jamma

Simply put, you first wire your Red, Green, and Blue to the Jamma fingerboard.

Second you have to make the circuit to split up the composite sync from the composite signal.
For this you need a LM1881N chip. I got one for 6 bucks total on eBay.

Wire it up just like the pic shows. I used a 8 pin harness to wire it up so I wouldn’t risk overheating the chip. Just wire up the harness and put the chip in after your done.

R1 = 680 K resistor
C1 and C2 = 100nf (0.1uF) capacitors

Don’t use Electrolytic caps. Use cheap ass Ceramic Disc caps they work the best and have no polarity (therefore it doesn’t matter which direction ya hook them up).
The resistor and caps you can find at your local electronics store for just a buck or two.

You can get the +5 volts from the Jamma cab. Just wire it straight from the 8 pin harness to the fingerboard.
When ya finish the circuit, just take the Composite sync and wire it to the video sync on the fingerboard and solder up the ground wire from the circuit and the Xbox cable. They go to the same place on the Jamma fingerboard.

Modded Double Dragon Cabinet

Oh by the way! You HAVE to solder a ground wire from video ground pin on the Jamma fingerboard to the main ground pin on the Jamma fingerboard. If you don’t the picture will spin round and round. All the grounds are going to the same place.

Now take your Jamma fingerboard and hook it up to the Jamma harness inside of the machine. Plug up the Xbox and test it out. If ya hooked it up right, you now have video on your Jamma machine!

My video was a little dim, so I found the controls on the back of the Arcade monitor and turned up the brightness. The Xbox doesn’t push out as much power as the original game. When I return to America in 9 months I will show everyone how to build a video amplifier for the machine.

Oh by the way, if you adjust the brightness on your machine be super super careful. TV’s, Arcade monitors, and Computer monitors hold a huge charge. If you touch the wrong spot, you will probably die! Seriously! Even if the machine is unplugged! I only did it cause I had to leave the states to come to China and did not have time to build a video amp.

Well we now have video. Now we just need sound, and controls.

I will post again soon and show you how I got the sound working from my Xbox on my Jamma machine.

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The Omega Machine (Xbox to Jamma)

bya Phil at 6:55 AM

Hi, I’m the other member of this blog. But so far no posts. I’m the one that does the dirty work behind the scenes. I’m the tech guy and am currently hooking up an Xbox to a Jamma arcade cabinet for my bro. It’s easy, but figuring it out alone can be a huge pain. Here’s how I did it. It’ll probably work for you, too, if you want to do it. But keep in mind, touching anything in a TV or something with big capacitors or transformers (even while off) will probably not send ya to the hospital if ya touch it in the wrong place, it’ll send ya to the morgue! So if you don’t know what a capacitor is, don’t attempt this. But don’t worry, I avoid all high voltages. And these steps only risk voltage as high as 12V. Just keep in mind if ya touch somethin bad ya could kill yourself inside that arcade cab there.

Step One in Xbox to Jamma – Build a SCART cable…

Sorry if I don’t have too many pics in this beginning here, I’ll describe it well, though.

My first step was to get video and audio output from the Xbox to the Jamma cab. Jamma picture tubes use red, green, blue, and composite sync. Well an Xbox doesn’t exactly output the same signals, but it will do most of the work for us.

Foreign Xbox users use a SCART cable which uses RGB with Composite Signal. We can use this but first we need to convert a US Xbox cable to a SCART cable.

Step 1 – Go out and buy a Composite Xbox cable with digital audio – $2.99 used.
I got mine for 2.99 but I think it was priced wrong, they normally cost a bit more.

Step 2 – Cut the end open so you can do soldering. You’ll have to pull the inside out to solder to the pins.

The inside will look like this…
When ya have it open you’ll see wires and crap soldered to it. Well if you get a composite cable with digital audio there will be 3 extra wires hooked up for the digital audio, probably a thin white, thin green, and thin red. Two of these will be used for our composite signal, the third we’ll just desolder.

The reason we bought a composite cable is so we don’t have to hook up the red green or blue.
WiringModify the cable so the soldering is like this. Be sure to add the extra jumper wire in there. As a composite cable, only two will be soldered on when you buy the cable. The Xbox uses these jumper cables to determine the type of output. We need the Xbox in SCART mode not Composite. Just add the third jumper wire to turn it into a SCART cable.The diagram shows the grounds for the red, green, blue, and composite joined together. You can join em at the other end of the cable. Just leave those wires alone for now.

Basically to sum it all up, leave it all as it is but find the thinner wires. There should be three: a red, white, and green. Desolder the green, solder the red to where it says Comp, and solder the white to the pin right beside of the Comp for the Comp Gnd. Now our thin red wire is our Composite Signal and the white is the Composite Ground. Finally solder the jumper pin as it shows. You’ll know how to do it cause it’ll look like the other two already hooked up. You’ll need a small piece of wire for this.

Your all done here so put everything back together and melt the rubber of the video cable back together where you cut it. Just about as good as new.

Finally splice the other end of the cable. You’ll have thick red, thick white, thick yellow, thick green, thick blue, thin red, thin white, and thin green. Splice the thicker wires. They’ll have two wires in one, inside of each wire is a white wire. The outside wire (not the white one) will be the grounds. Take the grounds from the video wires and put em together and add the thin white wire to it (comp gnd). There we go, now we have a partially finished RGB cable.

Here’s a diagram of the wires…

Yellow,white – Red Signal
Yellow outside – Gnd
Green,white – Green Signal
Green outside – Gnd
Blue, white – Blue Signal
Blue outside – Gnd

Thin Red – Video Composite Signal
Thin Whie – Gnd

Thick Red,white – Right Audio
This Red outside – Right Audio Gnd
Thick White,white – Left Audio
Thick White outside – Left Audio Gnd

Well we got RGB, Comp Signal, Right and Left Audio.
The jamma needs RGB, Composite Sync, and Mono Audio.

Our next step will be to get Composite Sync outta that Composite Video. For this we will need a LM1881N chip. I found one on Ebay for 6 bucks with shipping.

I’ll show you how to do this in my next post. Next step, separate composite sync from composite video.

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