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Old 20th January 2004, 02:12 AM   #1
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Default Computer SMPS and Gainclone

Can I take a standard computer SMPS, tie the + 5 and +12 wires together, the -5 and -12 wires together, and use them to power a gainclone at +-17VDC?

I have an old AT style supply that can produce 250W, so that could easily power a 3886 or 2 or something similar up to its full power.

Will this work?

Thanks, Mike
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Old 20th January 2004, 02:22 AM   #2
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no you can not do that because both voltages are referenced to the same ground. if you connected them together then you would probably blow the 12 or 5 volt lines (or both) or at least short circuit protection would trigger.

also you need complimentary positive and negative power rails for LM 38xx type amps.

If you want to use a computer PSU for an amplifier you could use the TDA7374 which is designed for car radios. so it will work on 12 volts. Dont expect any astounding sound quality out of it either (esp with comp PSU)
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Old 20th January 2004, 02:44 AM   #3
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Will a 3886 run off of a 24V supply?

If so, I could connect the +-12 and gnd to the chip, right?

or am i missing something?

-Mike
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Old 20th January 2004, 06:05 AM   #4
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the negative 12V is rated at an amp due to it being provided by a 7912 regulator...I dun think u'll be able to power ur amp that way...
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Old 20th January 2004, 08:10 AM   #5
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The -12V can supply only 500mA so you can use it only with a headphone
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Old 20th January 2004, 08:45 AM   #6
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It is a really low voltage to run it from. it will probably work though because the lm3886 will only put out 10 watts at that supply voltage (at 4 ohms) and only about 5 watts at 8 ohms.

(see page 14)
http://www.national.com/ds/LM/LM3886.pdf

so if my guesstimations are correct that is less than one amp being drawn from negative rail.
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Old 20th January 2004, 12:53 PM   #7
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OK, well thanks anyway, I just found the old supply sitting around and thought i could put it to good use. Since it was a 250W, I thought I could get more power out of it.

Thanks anyway, Mike
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Old 21st January 2004, 06:42 PM   #8
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If you dont decide to use the power supply itself, you could do as I plan to do and use the metal box from the psu to house your gainclone (minus psu bits inside, of course). It should have a nice dual pole switch and some vent holes - and as its metal you can mount your chip(s) to it as long as you insulate them
Then just spraypaint it your desired colour....

I'll post some pics of my one once I've finished.
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Old 21st January 2004, 09:45 PM   #9
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Yes, I am going to do that. Not with that supply though. I have a broken dell atx supply, and tore out all except the fan. The only switch on it, though, is the voltage selector switch, so it won't work for that. But it does have a nice fan and power cord connector.

-Mike
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Old 22nd January 2004, 11:55 AM   #10
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You can disconnect the Ground reference point (chassis connections) on a computer power supply and supply it with +12v from another computer power supply. As you can have these amplifiers in single ended mode you could chain 3 or 4 computer power supplies in series.

for 3 computer powersupplies its potential from ground on PSU#1 to +12 on PSU#3 would be 36 volts, and depending on the PSUs's used you would have roughly 36 volts @ 10 amps.. 360 watts. You can also adjust the output voltage on the power supplies, up to around 14 volts. giving you 42 volts. ofcourse 42 volts into a single ended amplifier @ 8 ohms is only going to give you around ~20 watts audio power
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