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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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whether you need to go with the "make your own AC" approach or the "Bypass the AC stage" modification will depend on whether your speakins in built amplifier design requires a negative voltage rail to function or not.
For true 0v crossing amplification, a negative rail is essential to generate the bottom half of the waveform under 0v. An AC input allows the power supply in a speaker/ambo combo to generate negative volts by half-wave rectifying the positive and the negative sides seperately. giving you +,0 and - outputs. If you bypass all that and feed it DC, then one half of the output stage wouldnt be able to run.
The transformer in a DC-AC converter design allows the output side to be at a different "zero reference" voltage than the input side. So if you are making a 0v-10v DC square wave into the transformer, by using a center-tapped output wind on the transfer, you can turn the 0-10v DC input into looking like +5v - 0v -5v - still a 10v span, on the output side, but with the "reference" center tap breaking it into the plus and minus portions of the wave.
So, if you amp uses the 18v AC input to generate a negative portion of the wave, then you need the DC-AC concertor to power them, if the speakers just rectify the 18vAC into +DC only then you can bypass the power supply and do what jake said..
If you're not sure, well, you have to multi-meter around for a bit in the power supply area and see what you can figure out. find the input diodes on the amps power supply and determine whether the AC input is being half or full wave rectified and what voltages its being turned into. An oscilloscope would help here, but you should be able to swing it with a multimeter..
_________________
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Sat Aug 20, 2005 5:12 pm |
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RoboWars Australia Forum Index
-> Off-Topic
Tested half of it today, just need to buy the full setup in a few weeks time. Sounds fairly good to me. Will sound better when the second set is put in and it is all mounted properly. Thing I like about it is the $90 cost 
If i had the cash spare, I would pick them up today while I'm in Brisbane (At LAN Cafe). The unit runs off 11.5v 1600mAh AC... or 18VA according to the power pack. I was going to look at finding a way of converting 12vDC (Car battery) to 11.5vAC @ 50hz to power the full unit. Oh the fun 
ALSO i tried foolishly to apply a positive current thru both the +12v and REM and ground out, which powered the units led up... but makes a regular scratchy (somewhat music related) burst through the speaker followed with silence then another burst and so on... If this is a componant failure im not too fussed seeing as its an ancient amp i basicaly got for free...!
sorry im a complete n00b at this (please dont kill me arron!)