[sdiy] removing dc offset

[gregory zifcak]

i see. so maybe what i'm feeling in the speaker cone is just the edges of 
the transition from zero to the dc offset? i get a thump at the start of a 
sound and a thump at the end. now i'm guessing that the capacitor passes the 
initial rising edge, then brings it back to zero, then passes the falling 
edge, and back to zero. the resulting pulses are filtered out substantially 
when i raise the filter frequency to about 300 hz.
hmm,
greg

>
>What happens if you take the cutoff below 300 Hz?
>
>If the DC offset is constant, it should be eliminated by _any_ size
>capacitor.  It's just that smaller ones will have a higher cutoff frequency
>and will attenuate bass more as the capacitor is decreased in size.  I 
>don't
>believe the problem is the filter slope.
>
>
>"gregory zifcak" <zifcak at hotmail.com> wrote:
> >this is what i was doing, but i have to use a cutoff frequency of about 
>300
> >hz to substantially reduce the dc. i'm assuming this is because the 6db
> >slope is just not steep enough.
> >i guess that because the toy originally used a small internal speaker, 
>they
> >didn't need to worry about the dc. i've added an output and i'm worried
> >about damaging speakers with the thump.
> >>
> >>Are you using a capacitor in series with the output as a DC blocking
> >>capacitor?  It needs to be larger for lower frequencies to pass through
> >>it.  It's really a simple highpass filter, so the larger the cap, the
> >>lower the cutoff.
> >>
> >> >--- gregory zifcak <zifcak at hotmail.com> wrote:
> >> >
> >> >> hi,
> >> >> i am modifying a toy that has very rich bass, but due to the fact
> >> >> that it is
> >> >> run from a single battery supply, there is a dc offset. i've tried
> >> >> filtering
> >> >> this with caps of various sizes, but i can't seem to get rid of the
> >> >> offset
> >> >> without getting rid of the bass. is there a simple way to do this?
> >> >> thanks for any suggestions,
> >> >> greg
> >> >>
> >> >>
> >> >>
> >> >
> >> >
> >> >
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>- Where merit is not rewarded, excellence fades.
>- Hydrogen is pointless without solar.
>- What good are laws that only lawyers understand?
>- The media's credibility should always be questioned.
>- The only good terrorist is a dead terrorist.
>- Governments do nothing well, save collect taxes.
>
>-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
>-- Linux Rex         | RedWebMail by RedStarWare
>-- FatMan: home1.gte.net/res0658s/fatman/
>-- NonFatMan: home1.gte.net/res0658s/electronics/
>-- Autodidactic Master of Arcane and Hidden Knowledge.
>