DC blocking capacitors

[lava_lamp]

Ive been looking at the DC blocking capacitors included in some of the headphone amplifiers, my question is this....Why is the DC blocking cap included on the input ?

This protects the amp and headphones from DC offset from the source but if the amp is made badly or the opamp develops a fault then the headphones may still be exposed to a DC offset. Why is the DC blocking cap not placed on the output of the amplifier ?

 

[guzzler]

this capacitor blocks any DC getting to the opamp (as you stated)... this means that any DC on the output is compensated for by the feedback loop (it goes to - on the opamp; think subtracting)... if there is DC in the input signal, this is not subtracted from the output so it should keep DC on the output to 0...

g

 

[tangent]

http://tangentsoft.net/audio/input-cap.html