Here's a simple LM3886 (LM3886TF) hard-wired amplifier I built during 3 evenings for my wife's ex Microlab Solo computer speakers (modded). I wanted to build it as fast as possible and using only parts I had at hands. Because the speakers aren't super powerful and never used aloud I took a simple $3 polystyrene box for the case and two old heatsinks for Pentium processors for cooling. I also had a power transformer taken from the Solo's dead amp. Originally I wanted to use inverted schematic with op-amp buffers (you can see a card with the buffers on the photo). Then I realized that it makes the box too tight and adds more hum because the transformer is too close to the electronics. So I took the buffer out and converted the amp to normal (non-inverting) gainclone. Without buffer the inverting schematic was oscillating at radio frequencies producing a lot of heat. Later I also removed DC blocking caps as the amp is intended for use with PC sound card which already has output caps. The switch the between volume knob and the headphone socket switches wires from input jacks between amplifier and headphones, i.e. headphones are powered directly from sound card.
Despite the small case I stuffed totally 55800 uF into power supply filters.
Unlike other "super simple gainclone" builders I always leave protective RC and RL circuits. "3 resistor amp" may look attractive and sound a bit better but removing the "extra" components greatly increases chances for a bad end of your speakers.
The amp produces a little static (hum) audible on my testing wide-range speaker but absolutely not audible on Solos because of their low sensitivity.
Working temperature of the amp in is just about 40 degrees so heat dissipation isn't an issue even with such small heatsinks if an amp is not used with continuous power exceeding a few watts. Working at full power for only a few minutes doesn't hurt it as well. BTW most of the heat comes from the transformer, not from the IC's.
The photos and schematics:
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08/24/09 12:23:46 am