Wednesday, July 1, 2009

Casing up the audio amp

The audio amp project turned out much better than I anticipated. There's just one hiccup to take care of before it's perfect.

First, a picture:

I had to cut a couple of square holes in the case to install a couple of the parts - namely the power switch and the power receptacle. So I just drilled a couple of holes in the middle of where the square holes needed to go and used a pair of files to enlarge them to the necessary size. It worked pretty well!

The right side is sort of the back panel and the left side is the front. The layout sort of winds up putting AC carrying wires rather close to the low voltage stuff, which is perhaps not the textbook way of doing it, but I don't intend to submit this thing for UL approval. The entire case is tied to ground, which ought to keep it safe enough once the cover is on and screwed in.

Note that each channel of the amp has the input grouped with the matching output. That way it's relatively easy to figure out left from right - in fact, there's no reason to label left and right, since the input is right next to the associated output. Of course, this might be a problem if your RCA cabling can't stretch far enough apart to hit both of them, but that's not a problem for my application.

You'll notice that leads from both sides of the AC in go over to the power switch. This is because the switch itself has a little neon light in it - it lights up when the unit is turned on. Bonus!

The one hiccup I mentioned above is that I put one of the big 2200 μF capacitors in backwards. When I applied power to the unit, it promptly started bubbling and smoking. The irony is that despite that, the amp works pretty well for brief periods. But I obviously can't leave it like that. I'm going to have to very carefully unbolt the heat sink, rotate the board up so I can get to the bottom, desolder and replace the blown cap and then put it back together - hopefully without wrecking the wiring job I did. Wish me luck!

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