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

[Richie Burnett]

> An amp or a CD player can have DC more or less right through
the audio path without problems...

This is very true.  I discovered it accidentally with a Cambridge Audio A1 
amplifier.  Had a single-supply audio DAC connected straight to the 
amplifier's input for a quick test of some synthesis algorithms.  No DC 
blocking capacitor, because I didn't have one at hand, and there's bound to 
be one somewhere in the amplifier, right!?  Everything sounded fine at low 
volume.  As I turned the volume up there wasn't even any of that annoying 
"DC on a pot" crackle, just a strange growling 100Hz hum.  Investigating 
further showed the speaker cone push forward as the volume was turned up! 
Whooops!  DC bias from the DAC output was being passed right through the 
Cambridge Audio amplifier's input circuitry, pre-amp, tone controls, and 
power-amp right to the speaker.  No wonder this amplifier is regarded as 
having a robust bass response!

-Richie,