Microphone preamplifiers: Do they really make a difference?
Firstly we have to assume that the preamplifier is of professional quality. Normally you would expect it to have an XLR microphone input connector and provide phantom power if required. In general you would expect such a preamplifier to be capable of professional work.
If your microphone preamplifier is of professional quality, then changing it for a different model may make a small difference in sound quality. However, the difference between preamps is tiny, compared to other factors that affect the recording process.
Normally you would expect a transistor preamplifier to amplify the signal from the microphone accurately. The differences between transistor microphone preamplifiers are very hard to hear.
A preamplifier that features a vacuum tube however will normally be designed so that you can if you wish create some distortion, which the ear can hear as 'warmth'. A small amount of warmth can be beneficial, but it is best not to overdo it as it cannot be undone later.
You may prefer the sound of one tube preamp to another, but once again we are talking about small differences. The average listener will not be aware of any difference between preamplifiers and will not care.
In short, there are many other things that will affect the quality and success of your recording more than the make and model of microphone preamplifier that you use. If you are currently dissatisfied with the standard of your recordings, it is almost certain that a different preamp will not help. Other factors need to be addressed before spending money in this direction.