I have a fire alarm that accepts a 25v line level speaker input at 4w, what is going to be the easiest way to play arbitrary signals over it i.e. from a 3.5mm jack, an amplifier and a transformer? are there small pre built modules for this purpose? Everything I see seems like it is intended for distribution to a large pa system not a signal speaker.
Edit:
It is a SSPK24-75WR
Here are some datasheets I could find, but there is not mutch info beayond "hook it up to our system"
http://resource.boschsecurity.us/documents/Datasheet_SSPK_Famil_Data_sheet_enUS_2736837259.pdf
https://www.gentex.com/sites/default/files/551-0070%20SSPK24WLP%20Series_0.pdf
Best Answer
Easiest is to use a 25V or 70V PA (public addressing) amplifier, e.g. first hit google for me. Since you seem to like Bosch, the have plenty of those too. You can surely find low-power cheap Chinese stuff. Your speaker has options for both 25V and 70V. There plenty of youtube tutorials how to hook that up, e.g. https://www.youtube.com/watch?v=M4I9TF4hVLI
Or build your own with a regular amplifier and an appropriate audio transformer. For yours, the transformer would be something like this or this (the latter has tap for 25V-5W too and is half-price of dedicated 4W one), assuming you don't want to power more speakers from the same amp/transformer. I have to warn you from my own experience[s] with similar 100V PA transformers that the labeling of the wires tends to be effing confusing and no two manufacturers seem to agree on where to put the ohms where the watts on those taps. So if you go this route, read the [usually skimpy] datasheet carefully and have a [AC] multi-meter handy.