The one in Sankt Annagasse, on the other side of the street from Hiltl, the oldest vegetarian restaurant in Switzerland and arguably one of the first to open in Europe. Behind it is St Annahof Coop, a quite extended supermarket chain.
This fountain is normally hidden by bikes and cars and it took a very tuned ear to find it. But, when you sit at the very popular Hiltl open air area, you can easily spot it.
Zurich 1200 Fountains 