Hello Elboroth2/ in response to your question yes that switch is for your class A biasing. The other switch to the left is for muting the inputs on the back when changing cables, respect these as i was recently changing xlr interconnects in a sa 102 dual mono setup and didnt have the switch engaged and a thump went through my system and I believe I burnt one of the ;hot; legs either positive or negative theres also the ground in xlr[three pins] but half my volume is missing in xlr. These amps are well made and its my fault but I purhased all plinius electronics in my home theatre since they come with a seven year warrenty repair is being taken care of, and I also have an sa100 mk 3 for my surrouds in a 5.1 setup.Your sa 102 in class A will generally take about 45 minutes and will get quite hot but my feeling in listening in this configuration the amp tends to produce smoother harmonic tones, cymbles decay a little longer as the stage becomes more dimensional,bass control is steller in both settings, most frequency change is on top regions, great amp in both configurations and as i also bought theyre m-8 preamp and theyre p-8 amp for my center channel. Theyre class A amps are all very musical with great dynamics and harmonic tones.Again this description of sound is a subtle change and I generally listen with no distractions to audibly account for the change, so for me; class A for contemporary Jazz or Classical and class AB for rock ect... Love theyre gear so I just wanted to share my own personal thoughts . Happy listening,Tim W....
