headphone preamps, suddenly no bass?

[Tony Hardie-Bick]

Chris Strellis wrote:

> Just a thought, is any one channel (L or R) worse than the other?  I'd be
> surprised both caps would have gone the same way.  Do you hear any big clicks
> when you plug in the headphones or input sources.  This would indicate a DC
> offset.

In any amp out, a DC offset is likely to reduce the bass response in headphones. 
  Like Chris says - you'd hear a click when you plug them in. Failing this, just 
inject some white noise, probe various parts of the amp circuit with a 
connection to an FFT application, and find out where in the circuit the bass 
response starts to roll off. Feedback network is the other thing that springs to 
mind (an electrolytic is sometimes used in series with one of the gain-setting 
resistors), but not if both channels are affected equally (that would indicate 
something simple, too obvious to notice, and probably nothing to do with the amp).

Check with several pairs of headphones first.

Tony (HB)