Audio Amplifier circuit refuses to work

Hi!

I want to build a clap switch, but somehow it doesnt seem to work.

At the beginning I tried this design: click

I checked everything several times, but it just doesnt do anything at all.

Then I tried several other circuits like this one or this one. But none of them works. In every circuit I used several different LM358s to eliminate them as a cause. On top of that, 4 different microphones were used.

The circuits were soldered and built on breadboards, with no improvement what so ever

The "amlified" signal looks like this: |500x154

and those "peaks" (which are often under 10mV) only occur when tapping really hard on the mic. the other stuff is just noise and changes all the time. the average voltage level jumps up and down by 100mV or so, too.

What could be the solution to my problem? I honestly ran out of ideas...

Cheers, Konrad

Basically that signal is not big enough for the software to work correctly.

On top of that, 4 different microphones were used.

Now were these microphones different types or just different microphones of the same type?

Some microphones require a supply voltage, like an electret microphone others like a crystal microphone do not require this. So you have to match the input circuit to the microphone type you have.

Also are you sure you are using the right value of resistor in the amplifier's feedback circuit. A 1M resistor is brown black green.

Can you supply a photograph of your amplifier along with the circuit of what it is supposed to be.

Hi again,

I built the circuit again on a breadboard, specially for good overview over the components. i even used new resistors, and now it works.

Then i measured the values of the resistors and saw that the 1Meg resistor is basically open circuit (my multimeter can measure up to 40Meg).

It was brand new, just taken out of its packaging...

Anyways, thanks for your help!

But ive got one question left: I dont quite get why the voltage peaks dont exceed 800mV (the peaks get flat tops then), even if i adjust the trim pot i used as r2- of course its enough for my application, but im just curious. |500x156

Cheers, Konrad

Clipping. LM358s don't have rail-to-rail output, at 5V supply they're only guaranteed to get 3.5V out.

You could increase the +ve output with a 10k from the 358 output to +5 rail - and improve distortion ( if you care) considerably as well...

regards

Allan

Hi, Which circuit did you use?

Can you post a picture of your project?

Thanks.. Tom... :)

Jiggy-Ninja: Clipping. LM358s don't have rail-to-rail output, at 5V supply they're only guaranteed to get 3.5V out.

Yes but he is getting a maximum of 800mV. That sounds like it is being clipped by a diode somewhere.

allanhurst: You could increase the +ve output with a 10k from the 358 output to +5 rail - and improve distortion ( if you care) considerably as well...

I find it hard to believe that a pull up resistor would help especially after looking at the data sheet.

The the OP, if your 1M resistor was open circuit the the gain you would have would be even greater that you need not less. Something is going on that we don't understand, so to understand it we need more information like Tom says.

You're right . It ought to go to 3.5v as it is.

The pullup idea is from a Bob Pease suggestion years ago.

It's also normal to use an op-ap in a non-inverting configuration in an audio amp because of it's better noise performance.

we need to know more.

regards

Allan

Grumpy_Mike: Yes but he is getting a maximum of 800mV. That sounds like it is being clipped by a diode somewhere.

You're assuming that OP's interpretation of the value as mV is correct, I'm guessing that it's not. If the raw ADC count is being sent to the Serial Plotter instead of a converted value, 3.5V with a 5V reference would be 716. 800 would be 3.9V, probably within a reasonable range of saturation level for that op amp. So it fits that interpretation.

konrad, what are you sending to the Serial Plotter?