Speaker audio distorted even though it is quiet

[rickymcmuffin]

I'm doing a project where I want to have a toy say audio clips when a button is pressed. Right now I'm trying to accomplish this with an STM32F407G-DISC1. I have a small speaker (16 ohms, 0.25 W) connected to my breadboard with the DAC OUT1 of the MCU powering it by playing audio clips. I have managed to play the audio but the issue is, the speaker is very quiet and distorted. However, when I put a 220 ohm resistor on it, it sounds much better but is even more quiet.

I just wanted to ask if there was anything I'm doing wrong. I'm new to this so bear with me. Would an amplifier help? I would assume not as the audio would just become more distorted. Any help would be appreciated!

[AScha.3]

you have STM32F4DISCOVERY board - right ?

and put audio out with DAC OUT1 of the MCU - ?

so this needs an output amp ! see ds , minimum load is 5K , with buffer ON .

why not use the onboard audio DAC (CS43L22) ( this has some amp also) ?

[STTwo-32]

Hello @rickymcmuffin 

As @AScha.3 Said, you should use a Resistive load of 5K ohm minimum and a Capacitive load of maximum 50pf (with buffer ON).

 

For more details, take a look at the part 5.3.25 of the DS8626.

Best Regards.

STTwo-32.

[rickymcmuffin]

Thank you so much @STTwo-32 and @AScha.3 . You're really clearing things up.

> why not use the onboard audio DAC (CS43L22) ( this has some amp also) ?

I am planning on eventually getting a different MCU and designing my own PCB which is why I'm trying to figure this out with only the built in DAC.

Just to be clear. I do need an amp. And when I use that amp, I will need to add a resistor with a minimum of 5K ohms. Is this all correct?

[STTwo-32]

Hi again, 

>I do need an amp. And when I use that amp, I will need to add a resistor with a minimum of 5K ohms. Is this all correct?

As you Can see under the figure53:

"The DAC integrates an output buffer that can be used to reduce the output impedance and to drive external loads directly without the use of an external operational amplifier".

I think this answer your question.

Best Regards.

STTwo-32 

[AScha.3]

no, nothing to add!   the amp should have high-impedance input , minimum is 5k . 

so you want drive a speaker ?  then you need a small power amp.

ie...