How much DC offset allowed in headphone amp?
How much DC offset can a headphone voice coil take before the sound becomes degraded? I can trim my Aleph headphone amp to be within 1mV of ground when warmed up (this takes about an hour ... excessive heatsinking).
How much DC offset does it take to actually damage headphones? Think Grado 30Ω cans here.
as long it's in the range of some millivolts, there isn't any problem I guess. Consider that some DC-protection circuits only work with a DC voltage of 1V or even more....
Anything below 10mV is perfectly fine for low-Z cans like Grados. 10mV into 32R (the nominal impedance of the Grados) is a paltry 3.1uW*. As your cans will probably withstand several hundred milliwatts of rms power before overheating, a few microwatts aren't going to hurt :cool:
Tthe desire for low dc offset isn't so much a quest to keep the coils from overheating, it's more about maintaining as much dynamic range as possible. After all, the dc offset will push (or pull) the coil away from its resting position, reducing the total excursion in one direction while uselessly increasing it in the opposite.
* - if you want to calculate this yourself, it's simply Ohm's law: P=(V^2)/R. If V is in mV, then P will be in uW.
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