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Everything posted by teragiga

  1. Hi all! This is my first post so, sorry if I would not be proficient in discussing electronics :) I am stuck in a practical experiment, I studied how amplifier for obtaining gain work. And I created a small circuit with an astable multivibrator, and operational, 2 resistors, two batteries of 9v: Something like this: Where the settings are : non inverting input. Rf = 300 K, Rg=150K And the expected gain should be : Av= 1 + Rf/Rg = 3. Doing a simulation I obtain something like this Where the output in volts of the operational is effectively augmented. But when I build the real circuit it doesn't happen: The oscillator generates a square wave that I can detect with oscilloscope and even with a tester (between -4.80v +4.80v ), the output of the amplifier is instead stuck to 7.8v. I have done this with a LM741, and also using a LM386 (one with single supply) and nothing. The crazy thing is that I obtain constant 7.8 v independently from the value of the feedback resistors (like they don't matter) and even if I completely disconnect the input. So, it is like if whatever I do with this configuration the amplifier saturates to 7.8v and end of the story. I also tried the inverting input configuration and nothing. Where is the mistake ? Or I completely miss something in what "gain" means ?
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