Hi Guys,

I am working on a prototype wearable device based on stm32. I am using generic eval board for class-d amp MAX98357A (3W) and a tiny speaker ABS-238-RC (Speaker, 500 mW, 8 ohm)

I have connected audio amp to stm32 (nucleo) using i2c (powered by its 33.V as well) and playing different tunes and also tried feeding mic input. All works fine except the audio output level is very low. I want atleast enough sound do be able to use it like a speaker phone. All googling says 0.5W speaker should be enough. I also set the gain to max level using a 100k register but no noticable increase in the volume.

Can anyone suggest what am I missing?
Or let me know what to test to check if I am doing it alright.

https://robu.in/product/adafruit-max98357a-i2s-3w-class-d-amplifier-breakout-board/
https://in.element14.com/multicomp-pro/abs-238-rc/speaker-8ohm-89db-0-5w/dp/2534984

Thank you.

 

Can anyone suggest what am I missing?
Or let me know what to test to check if I am doing it alright.

Is the 100K resistor from Gain to GND?
What does the voltage read on the SD pin?
What is supplying the 3.3 volts?
What is the voltage reading on Vin when playing?

 

With a 3.3V supply and an 8 Ohm speaker on a bridged output amplifier, the absolute maximum power out will be 0.6 Watts. To get more power out, a 4 Ohm speaker will give you a maximum of 1.2 Watts. The only other alternatives are to use a higher supply voltage or lower resistance speaker.

 

According to the manual the max output with 3.3 volt supply and 8 ohm speaker is 0.6 watt at 1% distortion or 0.8 watts at 10% distortion.

 

According to the manual the max output with 3.3 volt supply and 8 ohm speaker is 0.6 watt at 1% distortion or 0.8 watts at 10% distortion.

You are correct - I forgot to square the VRMS.
The TS stated that the speaker is "tiny". How tiny is it and how is it mounted/enclosed? That will effect how much noise it can make.

 

I suppose my initial question is that is 0.5 watt sufficient for speaker phone purpose?


Is the 100K resistor from Gain to GND? Yes
What is supplying the 3.3 volts? Yes
I will measure voltage and get back.