Amplifier

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. :frowning: 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. :slight_smile:

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.

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?

http://www.vellemanusa.com/downloads/0/minikits/manuals/manual_mk136.pdf
http://www.vellemanusa.com/us/enu/product/view/?id=351278

Cheers.

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!

*now

Sorry.