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powering PC speakers in a MAME cabinet
Sylentwulf:
Aren't car amps and speakers powered off a straight 12V from a car battery? Couldn't you use the same in an arcade cabinet off the 12V line?
alank2:
I too had many issues with the audio, and here is my audio story!
I first ordered a 20W amplifier from www.canakit.com, a UK194, which costs $14.96 assembled plus shipping. They make a smaller UK153 you might consider (5W). My speaker came with the cabinet and is single 6x9, 8 ohms, shielded. You can get the speaker at www.mikesarcade.com.
Because I went from stereo (output from sound card) to mono (one speaker), I used a 10k resistor on the left and right audio line. So you would have the Left line then a 10k resistor then the right line and another 10k resistor, then the 10k resistors hookup together and become your mono sound input. These resistors keep the audio signal from feeding too much current from left to right or vice versa when the signals are not identical. I then added a 47k resistor from the joined 10k's to the input signal on the amplifer to cut down the volume just a little more. Someone also suggested connecting a 15k resistor to ground from the 2 10k resistors to prevent more signal loss. I must admit that I don't understand what the 15k does, but things sounded better with it so I kept it.
I did have some trouble with potentiometers. I had the idea of mounting the volume switch through the cabinet, and I needed a new potentiometer to do this. I tried various ones, but couldn't get the one I needed (easily or cheaply) which was a 20K audio taper. In the end, I mounted the volume in the coin door instead of on the top of the cabinet as I hoped.
I did start with the PC power only to also find it has way way too much noise to be useful. Use a good quality power brick. Also add a large enough capacitor to help eliminate any noise across the power leads. Also, items like the fluorescent light will cause noise when flicking on and off. I handled this issue in one way so far by replacing the lights of america fluorescent light with an electronic ballast (www.fulham.com) and now no more flicker, it just comes on when I turn the cab on. There is still a noise in the amp when the light turns on, but at least it isn't on/off/on/off/off/on/off/on with respective noises. I have heard that putting a line filter on the fluorescent light will also help the situation. Mike at mikesarcade also has these. I am going to add one of these to the fluorescent light as well.
Make sure you use SHIELDED cable and that you connect the jacket/ground wire to ground. This will greatly reduce the noise in the audio signal. It is also a good idea to ground the heat sink on the amp itself.
In the end, I tore my UK194 apart and rebuilt a sound circuit based on one TDA2003 IC chip instead of the 2 it had. This resulted in much less current use (50ma instead of 200ma), but only 10W amplification. 10W will still more than enough for what I needed. I did this hoping to improve my potentiometer volume situation, but knowing what I know now, I would have just left the original UK193 intact and used it.
If you want a single kit with a TDA2003 amplifier, velleman makes one K4001 at www.vellemanusa.com.
Hope this helps!
Alan
southpaw13:
Hello, I used a 30 watt RMS car audio amp and it worked great! I turned the power gain down and had more than enough power. No noise problems...
krick:
--- Quote from: alank2 on March 01, 2004, 11:25:03 pm ---I did start with the PC power only to also find it has way way too much noise to be useful. Use a good quality power brick. Also add a large enough capacitor to help eliminate any noise across the power leads.
--- End quote ---
I found this dc power supply noise filter circuit in a book I have called "Do-it-yourself Projects for Guitarists" by Craig Anderton. He recommends adding this circuit to any power bricks that are adding hum to an audio circuit. It's a great little book. In addition to useful circuits like the one pictured here, there's plans for a DC power supply and a small 8 watt amp that would be perfect for driving cab speakers.
krick:
I just wanted to give an update. I'm still using the hacked "bay" speaker unit. After using it a while, it's really not that bad. Yes, the 0.75 watts per channel is really weak and the intermittent power supply noise isn't wonderful. But over all, it's actually useable, at least until I can settle on something better.
I may try to add the power filter circuit that I posted above to see if it helps any with the DC noise.
I've got a really cheap set of USB powered speakers on the way. They're a whopping 2 watts per channel but I'm sure they'll sound far better than what I've got now.
...
Krick