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Making 8 channel amplipifer for Octo board

Posted: Thu Jun 01, 2017 4:37 am
by DTF
I plan to use Octo as providing 4 stereo channels to 4 separate rooms of a home. Because of the installation I don't have possibility to couple active speakers to Octo sound board. There is a possibility to buy 4 stereo amplifiers, but for the reasons I will not going into this is not a solution which I prefer.

Since Octo board provide possibility to software control of each channel I prefer a custom made solution based on a single chip which has ability to drive 8 separate 5W speakers and which specs matches that of chip on Octo board. Is there more people who are interesting in that solution? Are anybody done such an amplifier already? Does anybody knows about some how to article about that somewhere on the net?

Re: Making 8 channel amplipifer for Octo board

Posted: Sat Jun 03, 2017 3:34 pm
by flatmax
Great question !

One idea is to use the .asoundrc file to do this. All devices would have to use the same sample rate and bits, so we use the dmix plugin to achieve this.
I have taken the example on splitting from here and modified it. It is untested, so please let me know if it doesn't work.

You can play to one of the devices like so :

Code: Select all

aplay -Done file.wav
aplay -Dfour file2.wav
Or using a video or different player :

Code: Select all

mplayer -ao alsa1x:two file1.avi
mplayer -ao alsa1x:three file2.mp3
Save the following to .asoundrc in your home directory or add to one you already have :

Code: Select all

pcm.dshare {
    type dmix
    ipc_key 2048
    slave {
        pcm "hw:0"
        rate 48000
        period_time 0
        period_size 1024
        buffer_size 8192
        channels 8
    }
    bindings {
        0 0
        1 1
        2 2
        3 3
        4 4
        5 5
        6 6
        7 7
    }
}
pcm.one {
    type plug
    slave {
        pcm "dshare"
        channels 8
    }
    ttable.0.0 1
    ttable.1.1 1
}
pcm.two {
    type plug
    slave {
        pcm "dshare"
        channels 8
    }
    ttable.0.2 1
    ttable.1.3 1
}
pcm.three {
    type plug
    slave {
        pcm "dshare"
        channels 8
    }
    ttable.0.4 1
    ttable.1.5 1
}
pcm.four {
    type plug
    slave {
        pcm "dshare"
        channels 8
    }
    ttable.0.6 1
    ttable.1.7 1
}
By the way, you can change the volumes by changing the last number on the ttable lines ! This may come in handy.

hope that helps.
Matt

Re: Making 8 channel amplipifer for Octo board

Posted: Sat Jun 03, 2017 10:23 pm
by DTF
Yes, that helped but first I need to do the hardware. Intention of my question is about hardware, and finding 8 channel amplifier chip to couple with Octo sound board.