[NBLUG/talk] a problem with audio noise

John Sowden jsowden at americansentry.net
Thu May 30 20:49:41 PDT 2013


On 05/30/2013 08:27 PM, jezra wrote:
> On the bright side, nothing exploded; however, nothing worked either.
> Right now I'm thinking of all of the electronic devices that I've taken
> apart and how I should have saved the ferrite doohickeys. grrrrr
>
> On Thu, 30 May 2013 16:22:07 -0700
> Mitch Patenaude <patenaude at gmail.com> wrote:
>
>> Another thing to keep in mind: Electrolytic capacitors are
>> polarized.  They need to be hooked up in the right way.  There will
>> be one leg labeled minus (-), and that leg needs to be hooked up to
>> ground, and the other to the +5 line.  If you get it backwards, you
>> may cause the capacitor to "vent" (i.e. blow up).
>>
>>    -- Mitch
>>
>>
>> On Thu, May 30, 2013 at 2:11 PM, jezra <jezra at jezra.net> wrote:
>>
>>> Thanks Frank,
>>> I have a few similar capacitors (a few 6v, one 10v, and some 35v) so
>>> hopefully something will work. The voltage going to the amp is 5v.
>>>
>>>
>>>
>>>> Jezra,
>>>>
>>>> Use a aluminum electrolytic capacitor.
>>>>
>>>> I don't know what the voltage of your power supply is.  5V?
>>>> Capacitor companies lie about their voltage ratings.  If you put
>>>> a 5V cap on a 5V circuit it will eventually blow up or short out
>>>> or just stop working. Multiply the voltage by at least two, or
>>>> better yet three. Get a capacitor of that voltage or higher.
>>>>
>>>> I don't know anything about your power supply or your amp, but
>>>> 100uF (micro Farads) should do it.  Smaller would have less
>>>> effect, but if that's all you have give it a try.
>>>>
>>>> Aluminum electrolytic capacitors look like this:
>>>>
>>>>
>>> http://image.made-in-china.com/2f0j00uBVtoMvqfNbl/High-Ripple-Current-Aluminum-Electrolytic-Capacitor.jpg
>>>>     E Frank Ball                efball at efball.com
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>
A few thoughts.  If the supply that you are putting the cap across is 
5.0v, I would use a minimum of a 15v cap.  Also consider the output of 
the bridge rectifier.  If it goes into a pass element (transisistor- 
3055 or whatever), think about the pass element shorting and the input 
volts going across the cap.  In that case, bump the volts.  I saw this 
earlier and the OP is not in the current msg.  Are you sure the noise 
you are trying to attenuate is from the Power Supply?  Try providing a 
pure DC (battery?) input to the power circuit and see if you have the 
buzz.  If so, it ain't the ps.  The word buzz make me think of a square 
wave as opposed to a 120 hz tone which the cap would attenuate in the 
PS.  Computers generate square waves, with beaucoup harmonics.  I don't 
have a solution for you if you are trying to get rid of square wave 
noise generated by the computer's clock.

Just a thought,

John



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