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[DPRG] Audio filtering

Subject: [DPRG] Audio filtering
From: Ed Paradis legomaniac at gmail.com
Date: Wed Nov 4 07:27:16 CST 2009

Assuming this is noise coming in from the power line:

You can run the MM5450 off a separate voltage regulator, or run the
VMUSIC from a separate voltage regulator. Or you can add a RC filter
on the VMUSIC power line.

If the noise is coming from EMI from the MM5450, you should look at
shielding.  I think what would be easiest would be to build a metal
box around the one part of the circuit and grounding it.  Since the
VMUSIC is a funny shape, it might be easier to shield the MM5450.

FWIW, I've never had to do this sort of thing.  Typically my problems
are solved by "separate power supplies" and "remove ground loops".

Ed

On Wed, Nov 4, 2009 at 3:39 AM, Scott Sumner <scottinthebooth at gmail.com> wrote:
> 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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