I had a couple of MXL 603's and a 67N (the transformer coupled version of the 603) lying in the studio that I wasn't using because the high end sounded so terrible. I read up on the mods that Michael Joly and others did to the capsule and the venting behind the capsule and decided it was worth a try to hack one of the capsules and bodies up and see what happened.
In the clip that I'm linking to below, I'm testing the 67N, since it was a little less lousy than the 603. The first part is the unmodded mic. The next section is the capsule mod (similar to http://www.audioimprov.com/AudioImprov/Mics/Entries/2012/12/5_Modifying_the_MXL_991.html). The third part is with the vents behind the capsule enlarged.
I think modifying the capsule make a tremendous difference, and might make the mic usable.
Here's the link-before you listen, note that the guitar had a weird vibrating high E string: https://www.dropbox.com/s/01gyb3456me7075/mxl%20capsule%20test.mp3?dl=0
In the clip that I'm linking to below, I'm testing the 67N, since it was a little less lousy than the 603. The first part is the unmodded mic. The next section is the capsule mod (similar to http://www.audioimprov.com/AudioImprov/Mics/Entries/2012/12/5_Modifying_the_MXL_991.html). The third part is with the vents behind the capsule enlarged.
I think modifying the capsule make a tremendous difference, and might make the mic usable.
Here's the link-before you listen, note that the guitar had a weird vibrating high E string: https://www.dropbox.com/s/01gyb3456me7075/mxl%20capsule%20test.mp3?dl=0