Thursday, May 10, 2012

150 W (3x50W) Desktop Amplifier




I have a nice 8" woofer collecting dust that I can't bring myself to throw away. So I decided to build a subwoofer for my computer desk to give a little more grunt into the 3" woofer desktop speakers I built. This will be an "ordinary" speaker in that it is simply ported, no equalization or other funny business. As a result, it will be huge. But that's not even built yet.

The glory of modern digital processing for me is crossovers. Active crossovers are complicated. A $10 computer sound card can now deliver cleaner, more decisive signal splitting than thousands of dollars worth of analog equipment. I'm going to let the computer split my lows to the subwoofer, and just provide the amplification.

I put in a new power switch, indicator, and a 50W LM3886 module with PCB of my own design (didn't design the circuit though, the manufacture example circuit works for me). Can find the manufacturer circuit here: http://www.ti.com/product/lm3886

Bolted to heat sink, wired up, ready to rock and roll.


The power transfomer is 330 VA capable, so I could add 3 more 50watt amps before power became a concern. I have a slow-blow fuse on that transformer since it dims the lights when I switch it on. There is just shy of 20,000 uF of capacitors on the DC supply.


Here's the additional channel amp, on the left side of the heatsink. Now the whole chassis can deliver 150Watt over the three channels.  Note the star grounding isolated from the case (at least here). This is because I have a ground loop breaker installed to eliminate any hum, but still allow the safety ground to work properly.



Now to actually build what this new channel will power :)


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