W A R N I N G !

W A R N I N G !

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Sunday, February 28, 2010

Save on those input capacitors!

What started out as a curiosity turned into a revelation -

What happens when the high-pass-filter of a source is connected to the input capacitor of the receiver? Essentially you get a circuit like this:

So I was wondering about the cut-off frequency. Ran a spice above and guess what, capacitor C2 doesn't have any effect on the frequency response.

Well it makes complete sense, as a capacitor in series will only block current if there is any flowing through it. In this case, there isn't.

Even if we model the input of the amp chip as having an impedance of 1M ohms, even with a 0.1uF capacitor (1/10 value of that above) changes to the frequency curve is minimal.

So, that 1uF capacitor was enough.

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