LM317 audio amplifier

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LM317 audio amplifier

Postby Harry Dalek » Mon May 07, 2012 9:33 pm

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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Harry Dalek
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Postby Steve Anderson » Tue May 08, 2012 12:29 pm

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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Postby Harry Dalek » Tue May 08, 2012 4:43 pm

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.



Hi steve i like it but when saw how much is wasted in heat puts me off thinking of trying it !
for my project i just needed a little amp and i did go for a lm386 i had handy .
I suppose if you find your self one day for who know what reason needing a amp had no transistors no ic's and only had this ...now we know another bit of electronics to store in the old head before we all go senile :shock:
OH steve off topic reading an old post you were showing the difference between a pwm and analog signal controling one of your crt monitors the pwm one was very clear in the gray scale test card the other you could hardly make out ....Is PWM the best way to modulate control a crt or leds ?
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Harry Dalek
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Postby Steve Anderson » Tue May 08, 2012 7:49 pm

Yes Harry, it is 'novel' but of little practical use.

As for the different modulation methods...that's quite a long story, one I'll get to when I have a bit more time than I do today. Long story short...there is no real 'best' way, they both/all have their pros and cons.

Steve A.
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Steve Anderson
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