[Zeleni Zec]

To answer question at the beginning of the thread, YES, every headphone is running on AC and only a very small number of amplifiers doesn't have capacitor at the input which eliminates any DC component of the signal. Only electrostatic headphones require DC bias to set working conditions (create electrostatic field between stators and diaphragm needed for proper functioning) but even them need an AC signal to create any sound.

 

[jaddie]

Quote:

To answer question at the beginning of the thread, YES, every headphone is running on AC and only a very small number of amplifiers doesn't have capacitor at the input which eliminates any DC component of the signal. Only electrostatic headphones require DC bias to set working conditions (create electrostatic field between stators and diaphragm needed for proper functioning) but even them need an AC signal to create any sound.

Minor addition, while input C may be important, every headphone output circuit needs to be designed for zero DC offset at the output, so it's either a blocking cap at the output, direct coupled output with DC servo circuit, DC offset null or comp, or just careful (and hopefully accurate) design for no offset.  Usually includes a power supply design issue.

 

[xnor]

DC is bad, but some amps output DC from the input at the output and even amplify it. Mini 3 comes to mind...

 

[jaddie]

Quote:

DC is bad, but some amps output DC from the input at the output and even amplify it. Mini 3 comes to mind...

Wow, that's nasty.  What does it sound like when you adjust the volume control?

 

[xnor]

Scratchy.

 

[mikeaj]

You wouldn't believe the number of audiophile gear that skips on the input (or at any point) cap for ideological purity or whatnot. But most of those do DC servo at output or have some other corrective measure. Some don't though, and not just DIY designs.
 
"No caps in signal path" is one of those marketing jingle slogan bullet points.