Henry is correct. The original idea was to include reverb in the Lunchbox, and the first production lot of panels was printed this way. Unfortunately, it became clear that it would be technically impossible to implement a decent reverb in the LB, due to some last-minute changes to the way our processor chip supplier decided to handle memory architecture.
So here we were with the finished PCB, but not quite enough memory to make a reverb. We decided to have a little fun with what was available, and designed the "ambience" control. Subsequently, the labelling was changed appropriately.
Later ZT models, the Acoustic and the Club, have dedicated reverb processors in them.
-k
ken.kantor@ztamplifiers.com