Here is what I do to an MXL 990 small diaphragm cardioid condenser microphone.

I remove the inner layer of the three layers of screen in the head basket. This opens the head basket somewhat, leaving the heavy outer layer for strength and the fine mesh second layer for RFI and hum protection. Some people remove the second layer as well, but I have had some hum pickup without it.

A ring of foam to damp resonance and maybe some paint finishes the body mods.

The modified capsule is remounted without the brass “halo” which seems to cause a dip in the upper midrange response. I suppose that ring is there to make the capsule look bigger, but it doesn’t help the sound in my opinion. It definitely upsets the balance of delay time around the outside of the capsule and through the diaphragm and backplate. Stick the ground wire under the capsule and tighten the mounting screws.

Replace the audio coupling capacitors.

If you paint the lower body as many do, scrape the paint off the upper edge so there is a good ground contact with the upper half.

So there you have it. It’s a usable mic in stock form, and it responds well to a few low-cost mods. The 990 is a popular candidate for replacement capsules and such as well. The circuit lends itself to easy modification for special purposes, there is a lot of room for larger parts, and you can’t beat the price.