ESP32 bluetooth speaker noise problem

[csibi]

Hello

I am trying to make a Bluetooth speaker. I use an esp32, that receives the media from Bluetooth and the microcontroller sends it to the internal DAC (8bit). The DAC pins are routed to the speaker. The sound has noise. What do I have to do to avoid the noise? I attached the connection, code, and sound sample.

 

[KlausST]

Hi,

I don't know your speaker specification....but are you sure the ESP is able to drive the speaker directly?
Usually one needs an amplifier to drive a speaker.

Even for high ohmic speakers I expect a DC blocking capacitor.

Is this your own idea/design? If not give a link to the document you used.

Klaus

 

[csibi]

Hello, thank you.
I used these two speakers: https://www.hestore.hu/prod_10037421.html
This is the library I used: https://github.com/pschatzmann/esp32_bt_music_receiver
I am using an amplifier but there is no difference except the volume. (I don't want to make the sematic more complex if there is no difference)

 

[KlausST]

Hi,

Some issues:
* the ESP is not made to drive 8 ohm loads. The current will be too high and the ESP may be killed sooner or later
* the ESP not made to drive inductive loads. The ESP may be killed sooner or later.
* the ESP can't output negative - true AC - signals, there will be DC component of about VCC/2 (without load). Audio signals are not made for DC, in best case an amplifier input will have a DC blocking input. A direvtly driven low power speaker (or erarphone) may be killed. You high power speakers will cause distortion.
* an 8 bit DAC is not suitable for some expectable audio quality. Even 1980s standard uses 16 bits ... which means 1/256 resolution.
Less resolution means higher quatisation noise.
* audio DACs need an analog reconstruction filter

Klaus

 

[Audioguru]

There is no noise but instead there is severe distortion.
If the system has a volume control then turn down the level until there is no distortion.

 

[csibi]

Thank you for helping me out.
I think the esp32's DAC only has positive voltage. I found this: https://www.adafruit.com/product/3678 (In my opinion with that I will get a negative voltage too.)
Is it a good idea?

 

[KlausST]

Hi,

It's an audio DAC ...that's what you want.
Add an audio amplifier and it's a perfect solution.

Klaus

 

[Audioguru]

The Adafruit schematic shows that its outputs have coupling capacitors then its output signals are AC that swing both positive and negative.
Maybe you damaged your esp32 by overloading its outputs with speakers.
Most amplifiers work fine with an AC audio signal (plus and minus) as their input.

 

[csibi]

I upgraded the setup and attached it. The problem is the following one: If I cover the Adafruit UDA 1334 with my hand it sounds great and has no noise. Without my hand, it is still noisy. What can be the problem?

 

[KlausST]

Hi,

No (unused) input pin must be left floating. So hopefully all the unconnected pins are pulled to a valid logic levels.

As far as I can see there is no connection between GND and AGND.
Try to do this. Maybe try a 100R at first, or simply short circuit them...

But ground signals on analog audio systems are critical. One good approach should be star wiring.

Klaus

 

[csibi]

Thank you for helping me out, it's fully working.