Speaker output in STM32MP157C-EV1 board

[Grodriguez]

Hello all,

I am trying to use the SPEAKER_OUT connector in the STM32MP157C-EV1 board to play sound using a set of regular 8 Ohm (non-amplified / passive) loudspeakers.

I am configuring the wm8994 to enable the SPKOUTL/RP path as described here: https://wiki.st.com/stm32mpu/wiki/Soundcard_configuration#Wolfson_wm8994_output_configuration

When I play a sound file via ALSA (using aplay), the sound signal is very weak. I can hear the sound if I connect a headphone set to the SPEAKER_OUT connector, but not if I connect the regular loudspeakers.

If I am reading the wm8994 datasheet correctly, the SPKOUT path includes a 2W amplifier. Do I have to do anything else in order to enable it?

BR,

Guillermo

[PatrickF]

Hello,

this post could help: https://community.st.com/s/question/0D50X0000BaLm50SQC/speaker-output-in-stm32mp157cev1

[Grodriguez]

Hi PatrickF,

No, I am already configuring the wm8994 as described in that post (which is the same info that was later added to the wiki, here: https://wiki.st.com/stm32mpu/wiki/Soundcard_configuration#Wolfson_wm8994_output_configuration)

I do get sound output on the SPEAKER OUT pins, but the signal is so weak (actually barely audible) that it looks like the wm8994 amplifier is NOT enabled. Any hints???

Guillermo

[PatrickF · Accepted solution]

Hi,

on the STM32MP157C-EV1 board, the Speaker jack is wired to SPKOUTxP outputs only (AC coupled single-ended with medium impedance), to allow a connection to an external amplifier (e.g. line input). It is not possible to connect low impedance differential speaker directly.

If you do your own board, WM8994 allow connection of regular speaker(s) to SPKOUTxP/SPKOUTxN as described in WM8994 documentation.

[Grodriguez]

Clear, thank you.