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[DPRG] Audio filtering

Subject: [DPRG] Audio filtering
From: Scott Sumner scottinthebooth at gmail.com
Date: Wed Nov 4 13:42:27 CST 2009

The AVR and the VMusic share a 7805 and the 5450 has its own 7805.  The
speakers are 12V so they go straight to the battery.  I can add another 7805
for the VMusic and see what I get...

Got any good examples of RC filters?

Scott



On Wed, Nov 4, 2009 at 8:27 AM, Ed Paradis <legomaniac at gmail.com> wrote:

> 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
> >
> >
> > _______________________________________________
> > DPRGlist mailing list
> > DPRGlist at dprg.org
> > http://list.dprg.org/mailman/listinfo/dprglist
> >
> >
>
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