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using computer speaker amp for portable sound system


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now i know i have the system thats in my school bag (the 12w x2), but i need one thats smaller, i have a small amp pcb from a pair of multimedia speakers.

it has the usual tone and vol control pots on it, but, its made to run on 12v AC from the mains transformer, but right after where the power leads solder to the pcb, there are 4 diodes and a capacitor, me thinks that is a rectifier circuit.

i tried running 12v DC (using the SLA battery from my bag system) into the amp and it sounded ok, but a bit distorted, if i tapped into the pcb AFTER the rectifier, and determined the polarity, it should be ok right?

im on holidays at the moment, when i get back i will get pics of my bag system for my other post, and pics of this amp

-ben

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  • 3 weeks later...

no probs, take out the rectifying diodes and put the battery the right way round. test it first before putting a big battery with a small pp3 for example, then use a bigger 12v one.
Many years ago, I was a busker and used the same thing connected to a guitar, I also found( and be careful here as this is probably an exception) some of these amps work even better on 15v giving a very clean sound.

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The 12V transformer has a peak voltage of 17V which is reduced to 15.5V by the bridge rectifier. Then the power of a single-ended power amplifier is 2.4W at clipping into an 8 ohm speaker.

When you fed 12VDC into the AC connections then it was reduced to 10.5VDC by the bridge rectifier and the power s only 0.88W at clipping into an 8 ohm speaker. A lot less power.

If you feed 12VDC into the DC side of the bridge recifier then the power is only 1.27W at clipping into an 8 ohm speaker.

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