Made from 1976, the Nagra DSM was a portable, self-contained mixer and speaker. It was designed to be used with Nagra portable recorders as playback equipment for location recording. It featured a microphone preamplifier and could also be used as a portable speaker. It is a very rugged and compact design but bears excellent specifications. 

Look at the “peclette” (ON/OFF/Batteries switch). It’s the first one that really looks like the ones of today.