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Connecting the LM4889 audio amplifier toa SparkFun MP3 shiel

Posted: Mon Oct 20, 2014 1:58 pm
by djburke
I'd like to use the LM4889 amp I just bought to allow a speaker to be connected to my SparkFun MP3 shield. The MP3 shield has - L and R contacts, so my thought is to connect (listing shield first then amp) one of L or R to AIN and - to G. However, there's a failry sizable warning on the tutorial page about Line out connections (you have to scroll down a bit to get to the correct part of this section) and the danger of a ground loop (and there's an associated datasheet for the VS10XX chip describing all this in more detail than I can follow). In this case this shouldn't be a problem, but is it safe to attach the - (aka GBUF) to the G pin on the LM4889, or does the ground line on the amp need to be "real" ground, rather than the 1.25V biased "Ground" that is GBUF (-)?

Thanks for any help,
Doug

Re: Connecting the LM4889 audio amplifier toa SparkFun MP3 s

Posted: Fri Nov 07, 2014 8:44 am
by paul
djburke ,

The amp definitely needs a high-current ground connection, so I don't think the GBUF is going to work well. Ground on the amp needs to be your system ground.

I think the VS10XX chip schematics show a capacitive coupling of GBUF to the reference inputs of the amp. If you look at the amp schematic though, I'm not bringing out the +(not-inverting input) of the amp, which is where I would have tried hooking up GBUF (or the audio line and hook up GBUF to Audio In line (AIN). So I don't think this is going to be ideal for you.

However - I would try this. Hook up GBUF through a 1 U (series) cap to the ground line, and then hook up the VS10xx audio line to AIN. I would bet that will work satisfactorily. If you have got it working by now (sorry about the really slow reply) I'd like hear your experience.

Paul