[sdiy] DC blocking caps on inputs - or not?

[Tim Ressel]

Hi,

Two things. First, some circuits need blocking caps because the chips 
input pin has a DC bias on it. Second, if you want to protect from fast 
transients on the input, use a 100pF cap to ground after the input 
resistor. This will take care of most hits including ESD.

--Tim (recovering EMC engineer) Ressel

On 2/6/2016 1:24 AM, Mattias Rickardsson wrote:
>
> Another capacitor question popped up:
> What's your view on having electrolytic caps right at the input of an 
> audio device in order to block DC and/or protect the circuit?
>
> I always have a smallish resistor and dual schottky diodes connected 
> towards rails at the inputs, and I hope this will protect from most 
> voltage spikes. Does a cap really add any protection here? The DC 
> issue can be taken care of later in the signal chain, and avoiding 
> input caps saves cost, space, and possibly audio quality.
>
> /mr - with golden [tinitus shower] ears
>
> Den 3 feb. 2016 8:01 em skrev "David G Dixon" <dixon at mail.ubc.ca 
> <mailto:dixon at mail.ubc.ca>>:
> >
> > I've read all these recapping posts with interest, but I gotta say, 
> I avoid using electrolytic caps except for power rail decoupling 
> purposes.  I never design them into actual circuits (and I've never 
> built my own power supply).  Same with tants.
>
>
>
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-- 
--Tim Ressel
Circuit Abbey
timr at circuitabbey.com

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