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Topic: Amplifier (Read 1 time) previous topic - next topic


So I build this circuit (scroll to bottom of page).

I made the same circuit as shown, but I used an LM358 and 5V arduino supplies. It works (yay!) but there is an annoying overlay of a high-pitched tone. So if I speak into the mic, it is my voice + annoying tone. All my cap + resistor values are correct, I double checked. If it helps:the overlay tone is ~868Hz, according to my tuner.

Is it the op amp that I'm using? The power supply difference?

Thanks for any help!


Well, you're getting away with a lot of stuff :)  The circuit is really designed to operate from split power supplies. By connecting the op-amp to +5V and 0V you are going to get a lot of distortion.

Try adding another 100k resistor from the '+' pin of the op-amp to its power supply (5V).

The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons


Nope. :( Now there's a softer whine, and no audio from the mic. Guess I'll just stop being lazy and put together a +/-9V supply like I was supposed too. :)


It'd not works, link you posted shows OPA powering with +-9V.
Nothing wrong with a chip , it was design for:

"Single Supply Quad
Operational Amplifiers"
and they say:
"can operate at supply voltages as low as 3.0 V "

What is an error?
You have to change a circuitry when you powering single supply.
+input of the OPA has to be biased to half  of power voltage, one more resistor 100kOhm required
to be connected between +input and +5V
And capacitor in the negative feedback, would be helpful to prevent HF osculation.


Mar 06, 2011, 08:11 pm Last Edit: Mar 06, 2011, 08:12 pm by baum Reason: 1
But the 100k resistor didn't work- It just made the output REALLY soft. I'll just do dual supply.

And where should I put the HF cap?





I'll try that... Thanks.

(The circuit mentions an "8E2" resistor, is this 8x10^2, or 800?


It's 8.2 Ohm, my opinion, it's not necessary, as IC 5532 has overdrive (shorting output) protection.
For LM324 , the same:
• Short Circuited Protected Outputs


OK. Now I built my split power supply, and it works! But, if I am not grounded, there is this annoying low buzz. When I am grounded (touching long wire, metal table, any large metal object, it is crystal clear. Any ideas?

Thanks for all the help so far! How I can spy of people!


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