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[DPRG] Audio filtering

Subject: [DPRG] Audio filtering
From: Scott Sumner scottinthebooth at gmail.com
Date: Wed Nov 4 02:39:45 CST 2009

Hello all

I have a question regarding audio filtering.  A project I'm working is
playing music via a VMusic2 and blinking LEDs with an MM5450 LED driver.
When I plug in external computer speakers to the VMusic everything sounds
great.  When I transfer to the project speakers however (powered off the
same 12V battery as the LEDs and VMusic) I get a very bad hum and/or buzz.

I've already eliminated a ground loop by only connecting the signal wires
and not the shields feeding the speakers.  That helped significantly but
doesn't completely eliminate the problem.

Further investigation appears to point to the MM5450.  As the LEDs blink you
can hear the buzz change relative to the number of LEDs lit.  If I
disconnect the power to the MM5450 the buzz goes away completely.

So bottom line my question is this.  How can I filter the power going into
the MM5450 and/or the speakers to ensure that both receive sufficient power
but "feedback" doesn't get into the audio system and/or the speaker power is
isolated from the electronics?

Thanks,
Scott
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