I found this pretty interesting.
http://electroschematics.com/6684/lm317 ... amplifier/
Moderators: Dave Moll, Steve Anderson
Steve Anderson wrote:Interesting, yes, efficient no. Even with no output the circuit draws 450mA (4.5V across 10 Ohms), which with a 9V supply is just over 4W. It's a classic Class-A amplifier with 2W dissipated in the '317 (hence the heatsink requirement) and 2W in the 10 Ohm resistor. Which if it produces 1W is only 25% efficiency, and I doubt it does produce 1W as the '317's internal voltage drop will limit that.
The input impedance is also very low, in the order of 1K! Note the rather large 10uF input capacitor to keep any semblance of reasonable LF response.
Sincerely, for just one Watt, use a LM380, LM386 or even a TDA7052, just as simple and not gas-guzzlers.
Steve A.
P.S. I also wonder that without output bypassing whether the thing might be stable or not.
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