So I did toast the chip last time. This time I was more careful in testing. I built it on a protoboard, with the pins on either side. The chip is held in place by the wires soldered to the pins, as well as the pins squeezing the board. For an enclosure, I used an old Zapco AG150 I had that doesn't work. The clips that were inside were used to hold the chip to the heatsink. The bolts that held the board down were on rails, and exactly the right distance from the heatsink for the holes in the protoboard I used. I could not have planned it better. I isolated the chip from the heatsink with a pad that was used in the amp for the same purpose, even though the back of the chip is tied to ground. Arctic Silver 5 used on both sides of the isolation pad. Now, even with only 11.5V and an mp3 player source, it's quite loud. There is less bass on the front channels like I had planned. I'm going to use a pair of 6 pin keyed molex connectors for all inputs and power to make installation easier.
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R.I.P. #2. Tested many times with bench supply. Final test was with the wiring harness and cd player that was being used in the car, lid on the amp and everything. Plugged in the power in the car, lots of smoke, then a fuse blew in the car. Post mortem shows nothing wrong except the chip is slightly melted and split along the edge near the pins. Shorted internally. My best guess is the heatsink clip was putting too much pressure on it. At this point I've spent as much as a cd player with built in amp (the chips are over $40 shipped), so I'm giving up. Let's hope my bridged LM4780 goes a lot better!
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