I need a fixed gain preamp that will increase the output level of my Shure dynamic mic, so that it will be similar to the output level of my condenser mic. I think 20 dB of gain will be enough.
Consider these products:
Cloud Lifter Preamp (model CL-1) from Cloud Microphones. It operates from phantom power and provides 25 dB of fixed gain.
Fethead from Triton Audio.