OPi Zero : how to configure sound output in mono ?

Hi,

I'm trying to put my OPI zero in mono instead of stereo by default.

On ARMbian my alsa config file (/etc/asound.conf) looks like this  :

pcm.!default {
    type plug
    slave.pcm "dmixer"
}

pcm.!dmixer  {
     type dmix
     ipc_key 1024
        ipc_perm 0666
     slave {
        pcm "hw:0,0"
        period_time 0
        period_size 1024
        buffer_size 4096
        rate 44100
                format S32_LE
                channels 2
    }
    bindings {
        0 0
        1 1
    }
}

ctl.!dmixer {
    type hw
    card 0
}

I tried to add something like this but without success :

pcm.makemono {
    type route
    slave.pcm dmixer
    ttable {
        0 1    # in-channel 0, out-channel 0, 100% volume
        1 1    # in-channel 1, out-channel 0, 100% volume
    }
}

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I'm probably making something wrong... Any advice please ?