One easy way to do this is to route it through an analog tape machine for some quick and dirty 'warmth".

Assuming you work with a DAW (and can do nonlinear editing and sliding tracks around in post) buy a decent used 2-track reel to reel machine. You can get some great deals for around or under $200 depending on what's selling on Ebay or even your local Craig's list.

Clean it and service it for the kind of tape you'll be able to get, probably the equivalent of Ampex 456 (or whatever Quantegy calls it nowadays).

Load up a reel or tape (or make a loop if you're handy enough) and set the tape to record-line in/repro out. If you're doing this after the fact, you'll be using it as an effects loop. If you're doing this while recording into the unit "live", there will be some offset to correct after the track is cut. (Your processed material will be late by whatever the factor of the distance between the rec and repro heads and the tape speed, so youll have to adjust for that.)

You can even route an entire mix through something like that, adjusting the wet/dry amount to taste using your DAW. (If you want to REALLY go commando, try to find a 3-head cassette deck - probably a tascam or or Nakamichi and use that instead.)

You might want to try to add some light compression? I find a full dynamically unaltered vocal can sound a little hard and the light compression will help to smooth it out and make it appear warmer.

In a way it is similar to what JoeH has recommended. The analog tape can have a type of compressed quality to it, which will helps to make the vocal appear warmer.

When recording vocals, most folks use a cardioid pattern microphone which all have proximity effect. That means that the closer you are to the capsule, the more bass response you will hear. So it's good to learn just how far to be from the capsule to provide the kind of warmth you seek. Frequently the bass will appear to be too exaggerated and when that happens, that is when you switch on the high pass filter on the microphone which will suddenly make the vocal sound crisp.

So you don't necessarily need to purchase a different microphone preamplifier or microphone. What you do want to do is to learn how to manipulate the equipment you currently have.

What's that button do??
Ms. Remy Ann David