Does an op-amp based pedal harm my real amp ?

[seadi123]

Hello I see a lot of distortion schematics using lm386 or other kind of op-amps . I know this small IC can give an output of 1/2w , sot will this high output signal harm my amp ? Let's say i have an 1/4w 5% resistor in front of the amp circuit , it would burn immediately . Am i wrong or i'm missing something ? Thanks

[Mark Hammer]

Think about all those times you saw an amplifier's specs.  They would likely say something like "40W into 4ohms, 20W into 8ohms".  Your typical LM386-based pedal is going to be feeding that mighty 1/2W into at least several thousand ohms via its volume control.  As a "power amp" the ratings for the 386 assume it is feeding 8ohm speakers, or maybe 32ohm headphones.

Have no fear.  Your amp is safe.

[PRR]

> this small IC can give an output of 1/2w ,
> Let's say i have an 1/4w 5% resistor in front of the amp circuit , it would burn immediately

As Mark is sayin'.... half-Watt or 0.5W in say 8 Ohm load. 0.05W in 80 Ohm load. 0.005W in 800 Ohm load. 0.000,5W in 8K load.

POWER is Voltage AND Current.

High-value resistors won't take current easily.

The guitar-amp input resistor is normally near 800K (often 1Meg or 1,000K). I've run out of thumbs to count zeros, but I'm sure it is far-far-FAR under 1/4W.

But what's the WORST can happen? The smallest to-ground resistor I have seen on a guitar amp is 47K or 47,000 Ohms. A 9V powered audio amp can make 3V clean 4.5V max-fuzzed.

4.5V squared is 20.25V^2.

20.25/47,000 is 0.000,43 Watts.

About 2% of your 1/4W resistor's rating.

[Psychopath]

http://www.diystompboxes.com/smfforum/index.php?topic=59920.0

[seadi123]

Now I understand Thank you very much guys