I had to scrounge around the parts box, but I found everything I needed. First I tried the circuit shown in figure 1 here:
http://gilmore2.chem.northwestern.edu/projects/meier_prj.htmThe results were interesting to say the least. It did drop the overall output by maybe 8db, so it is hard to get a 'flick of the switch' comparison (I wired it into the output with a 4pole 2throw switch). The circuit definitely attenuates the bass quite a bit, while at the same time excentuating the treble. It's not as bad as it sounds. It actually is quite non-fatiguing to listen to. I miss the bass at first, but after a few minutes you get used to it and the depth of detail seems to increase greatly.
I then decided to try the enhanced bass version shown here:
http://gilmore2.chem.northwestern.edu/projects/meier2_prj.htmI used the values for 'medium' crossfeed level. The bass improvement was not huge but surely a little better. I'm going to see if I have parts to try the 'high' crossfeed level.
One strange thing I noticed, with the enhanced bass version I can hear a difference in the response when grounding the center cap, but only when one side of my phones are connected. If I have both channels connected I can hear no difference when grounding the circuit. I wonder if this has something to do with the resistors on the output jack.
