Bro57, the Black Widow tends towards brightness, so I would be leery of putting any type of MC on it, not because of lack of quality (I tried an MC on it and it worked OK, but did not sound terrific), but because it is bright. As well, I think the Grado is easily superior to the cheaper Denons, excepting, of course, the classic DL-103 which, being low-compliance (I believe), would be a poor match for your tonearm. Don't buy into the MC hype, get yourself a good high-compliance MM, you'll see, you'll be surprised at the amount fo detail and dynamics these can give when set up optimally.
Rwwear, if I remember, the Carnegie is a high-compliance cartridge, is it not? And as to the Shure being "mechanical" sounding, I have heard this said before, and this may be due to a mismatch with electronics and so forth. In my system and other systems, it was liquid and supremely musical, and I would just play record after record and forget all about audio crapola, and believe me, this was bliss. If the Carnegie was high-compliance, I would suggest it sounds as you say because of this. Perhaps this, after all, is why MMs are simply better than MCs at preserving/presenting that rhythmic interplay which is so important to the music (this has been noted by seevral audiophile acquaintances of mine, once we get over the flavour of the day stuff).
And Listener57, you're absolutely right, money is not the key to music: a little knowledge, and trusting your instincts ("Hey, I like this! as opposed to "Hey, this is really impressive") is the key. I find that truly musical "budget" pieces are far more numerous than musical "high-end" pieces. Musically flat but extremely detailed equipment prods the unhappy owners to buy ever-more expensive equipment in an attempt to justify the ridiculously high outlay for a lot of this stuff. The more information a piece retrieves, the more difficult it is to preserve the music, which ends up just getting dissected, and the timing evaporates. Without timing, stereo equipment is good for boat anchors. Find a used Grace or Mayware - both cheap - for your Grado, and you'll hear what I hear, an opening up of the Grados, greater slam, more information at the frequency extremes. On a Black Widow on an Ariston RD80 (not particularly notable, but very musical) the Grado Platinum is a bass monster. And don't forget, these cheap tonearms benefit just as much as Regas do by re-wiring. I've just bought an ASL Mini Phono stage for $250 with NOS tubes classics new, and I can't wait to hear the Grado through it! I'll be reporting on it in the ASL Mini Phono thread later.
