Controls I to P show the error status of the MA12070P. If there are no errors an “OK” string should appear in
each control. It should be noted that “Err pllerr” will show an error when the Raspberry Pi is booted. After any
audio signal has been played the control should show no errors.
4.5.2 Volume and limiter settings
In order to not reach maximum output current limits of the booster and its inductor it is necessary to set the
limiter values properly. In relation to this point, a protection mechanism has been implemented in the HAT,
which will mute and disable the MA12070P amplifier when the maximum output current is reached. In order to
set the correct limiter settings for a specific loudspeaker impedance, the following procedure should be
applied:
1. Enter the alsamixer in Raspbian or Volumio.
2. Turn the limiter control “Lim thresh Volume” down to -40 dB.
3. Set the volume control “Mstr Volume” to 0 dB.
4. Turn up the volume of your audio source (phone, computer, etc.) to maximum.
5. Start playing music.
6. Start carefully increasing the limiter control in 1 dB steps while looking at the current limiter level. Here
there are two possible results:
a. When the maximum output current has been reached, the device will mute and it will be disabled.
b. The Raspberry Pi has been rebooted automatically because of the voltage drop of the power
supply being used.
7. Take note of the last limiter threshold value that was reached.
8. Reboot the Raspberry Pi and set the limiter value to 1 or 2 dB less than the last value reached before the
reboot.
9. If no limiting at all is desired on the audio signal at full scale, set the volume to the same level as the
limiter value found in step 8. However, this will reduce the loudness of the system. If maximum loudness
is desired, maintain the volume at 0 dB.
10. If it is necessary or if the device is muted and disabled again, reboot the Raspberry Pi one more time and
reduce the limiter threshold by 1 dB more.
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