Yes, there are quite a few little boxes that do the trick. If you google for spdif and analog instead of spdif and audio, you get a slightly different variety.
I also have an older audio interface that works as a standalone converter.
If mic is the only input you can use, you may need a DI box and/or pad as the RCA output level may be too high for the mic input and the input impedance too low for the RCA output.
Make sure that you turn off the phantom power of the mic input.
Wilko