Bater,
I looked up your Mic, the NADY SP-1. It is a dynamic Microphone and doesn't need a Preamp for you to use it. Any place you can plug the cable into should be OK.

If you buy a Condenser Microphone your ART Preamp should work just fine. This Preamp uses a 12ax7 tube. The 12ax7 has been used for years and is a perfectly acceptable tube for low noise audio circuts. It was probably used in Pro Tape Recorders before Solid State became the norm.

A Preamp is a very basic circut that (In this case) is a two stage circut, the 12ax7 is actually two tubes in one envelope ans is cascaded in series as so it will amplify the signal twice.
Many years ago the EIA, Electronics Standards Industry Association set the standards so one peice of gear would be compatiable with another peice of gear. So when you plug a Microphone into a computer a dynamic mic will work as designed.

Your ART Preamp will work with any Condenser Mic because of the Industry Standards set many years ago.

Your Nady is a low end dynamic mic and a better mic, even another dynamic such as a Shure SM-57 may eliminate the harshness you are experencing.

Ray E. Strode