Operational Amplifier not working?


I'm trying to use the KA324 IC (which consists of four opamps) for amplifying an audio signal.

I've tried almost every schematic from this website: http://sound.westhost.com/dwopa.htm
and also from lots of other websites, but none of them work.

If the output volume is Really low, the sound is pretty good, but very quiet.
When I turn up the volume, the sound is really bad, I almost can't recognise the song I'm playing.
The output volume is also not that really high. If I keep increasing the input voltage, the output stops increasing after a while. It's not really 'loud' at that moment too.

I've connected the IC to 12V DC (between the two middle pins). The + input goes to the ground connection, the - input goes to my POT voltage divider of the input voltage. The output pin goes straight to the speaker.
I also added a 100kOhm resistor between output and - input. Without that resistor, I hear nothing at all but I think that's normal.

I've also tried the three other op-amps from that IC but no luck.

Is this opamp just not ment for audio amplification? or am I doing something wrong?



sort by: active | newest | oldest
Since steve and g have pointed out that this is NOT a power amplifier - rather it would be better suited for a preamp (that's to bring the signal up to a usable level FOR the power amp) - I would also like to point out that it sounds as if you have connected the power backwards. Positive should go to pin 4 (VCC, middle on the left as you are looking down on the top) while negative should go to pin 11 (GND, middle on the right as you are looking down on the top. What purpose does the voltage divider perform? 12V is within it's range.

For further help, you should post a pic or actual schematic of how it is currently hooked up. Just draw the opamp as a block (with pin 1 marker) and the pins coming out and show how things are physically hooked together. This would tell us a lot about your build.

Yes,. absolutely right. Electrorials: Don't TALK circuits, draw them.

Here's the PDF of the datasheet. It does not need a split supply, though it can use one. However, It has been pointed out that it is a small signal device, not a power device. Follow the advice given elsewhere in these answers and look for a stereo audio power amp IC that uses 12V. Do you still have the original? If so, what are the numbers on it?

sshuggi4 years ago
By the sounds of it, your opamp is only operating in the positive... I've connected the IC to 12V DC (between the two middle pins) The opamp needs something like a +6V and a -6V in the power terminals as apposed to +12V and 0. That way, i can actually amplify sounds when the signal swings into the negative. And it does with audio.

Another reason it might be sounding bad is you're clipping the signal. Say your gain(amplification) is x15, and you have a waveform input that reaches+/-1V. With your current configuration, it will try and amplify the signal to 15V, but all it has to work with is 12V on the positive side. So, the signal is amplified normally up to 12V and then flat lines from there until the input goes back down. With any negative voltage signal, all it can do is output 0V... This is possibly what is giving you poor sound, especially when you try and turn it up.

Like everyone else is saying, this configuration only gives as much power as whatever is powering the opamp. If that's a battery, don't expect much more out of it that mini speakers.

Something to think about: Before you go hooking everything up to a massive power supply, check the ratings on you parts. The opamp has a limit to the current that it can output and the speaker has a max wattage.
P=I2R   The standard minispeaker has R≈10 Ohm and P≈0.5 W. Plugging this into the equation, the max current is something like 220 mA. There's probably other things to consider, but just know the limits of your parts.
gmoon4 years ago

More than likely the KA324 isn't designed to drive a speaker load--it has a different (higher) output impedance. And low current handling...

I took a quick look at the datasheet, and in the specs it gives the two values (under Voltage Swing) for load resistance--2K and 10K.  You're using a speaker as a load--what's that, approx 8 ohms? Pretty far from the load.

In short, a general opamp isn't a power amplifier. This would be an appropriate chip for a preamp, or a mixer or something similar. Something early in the signal chain. But it's not the chip to drive a speaker load.
An op-amp is NOT suitable for "power" amplification, and it sounds like you are operating it "single ended", when it really needs either split supplies, or special input biasing arrangements.