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Using PC Power supply for 7.5 volt power adapter
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DeLuSioNal29:
Great idea for a full sized cab, I love it and will probably use it on my next full sized build, thanks!  But this hack will be for a Vigolix clone for my 6 year old.  So there is no back to the mini arcade.  :banghead:

D
dkersten:
OK, if you are set on using the psu for the master power, you could also use a simple bosch style 12 volt relay to jump your 110v over to that wall wart.  The typical 12v 30a relay is good for 3 amps at 120 volts on the switch side (12v trigger). 

(see below for diagram)
Pin 85 to ground on the PSU (black)
Pin 86 to the yellow wire on the PSU (12v)
Pin 87 to the black wire on the 110v (where your monitor power is tied in)
Pin 30 to the wall wart (small spade on the plug if polarized, otherwise just one of the two spades, doesn't matter which)

Then the other spade of your wall wart to the common 110v (white)

When you turn on the PSU, the relay will close 87 to 30 and turn on the wall wart and you get 7.5 volts for your audio..
lilshawn:
this is a good option. that way it turns off and on with your other power.

another option is to wire a powerbar inside the cabinet and plug everything into that. that way, when you hit the main power switch...the bar gets power and your power supply for the game, speaker adapter, and monitor all get power at once.

ADDENDUM:

the reason powering it with the power supply like i mentioned won't work in this case is because the shield of the audio output jack of the computer (or xx-in-1 board) is tied to ground internally on the board. that means all the black wires in the powersupply and all the exposed metal on the chassis are tied to the black "ground" connection. (this includes the USB and the shield connections on all the IO ports and monitor connectors...even the metal case itself.)

when you power it with 7 volts from the power supply...the audio input plug on the speakers is also integrally tied to ground. (to keep noise from entering the audio amp and causing buzzing.)

when we power it with the (-) lead attached to the 5 volt line to get 7 volts it is effectively attached to the shield of the connector.

if you leave it unplugged, nothing would happen the speakers would operate normally (plugging an mp3 player would have it working fine)....but as soon as you plugged it in to the ground sheilded audo connector on the board, the power supply would shut down (hopefully) because the 5 volt on the shield now is being attached to ground and shorted out. worst case scenario is the power supply continues to power the 5 volt rail and melt all the wires into a fiery mess.

CONCLUSION:

powering items straight out like fans or LED's or motors using a mixed supply like this is fine. but not for anything that is attached BACK to the computer through another connection (IE: audio,usb,serial,video,etc.) or anything that will be attached or touch to the metal chassis of the computer. (because the screw holes on the board may be tied to "ground")
DaOld Man:
DOH!
I didn't think about the ground either. Don't use your pc power for this project!
EDIT: Don't use your PC power +5 and +12 to get 7 volts.
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