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Op Amp distortion - the resolution

Thanks to the help received here, my stage monitor is now working properly. As recommended, power pins decoupled at the ICs, 100 ohm resistors fitted to isolate the output pin from stray capacitance to ground. I did manage to borrow a 'scope, and even after applying the remedies it was clear that crossover distortion was still present - it looked on the screen just like the drawings in the text books. Well, I s'pose it would really, wouldn't it!!

It all went away after replacing the LM358 with a TL082 in both parts of the circuit. It now sounds sweeeeeeeet !!!! Thanks to all - but especially Phil Allison and Eeyore - for the good advice.

Reply to
Mike Faithfull
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It's possible the simple opamp replacement would have worked, without the new supply bypass capacitors and the output-capacitive-load decoupling resistor, given the superior characteristics of even a low-end JFET opamp, such as a TI's TL082, with its class-AB output stage, higher loop-gain-bandwidth f_T, and good phase margin with capacitive loading.

Do you wanna try removing the added parts to see if it still works? Understand, we recommend that you put 'em all back again, even if it does work OK. But still, it would be an interesting experiment. Are you game?

Reply to
Winfield

** The TL072 /082 series are in fact *notorious* for having poor ability to remain stable with capacitive loads - making an additional resistor in series with the output almost essential.

Go look up the published schematic.

You may notice the cause.

...... Phil

Reply to
Phil Allison

(snip ..)

Not a chance! It's working now and that's how it stays !!

Reply to
Mike Faithfull

Yes I see the extra output resistance, good point. Still, it's gotta be better than the LM324, LM358, etc., so it'd be interesting if Mike were to play the game. He could test the added output resistor aspect by temporarily shorting it out.

Reply to
Winfield Hill

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