The tap is set for 8-ohms at the factory. I think you have to remove the rear panel to access the tap to change it to 4-ohms to match your speaker. From what I've heard, operating the SF Power 1,2 and 3 at 8-ohms with any speaker is not a problem nor has any detraction to the sound. But at 100 watts into 90db speakers not enough volume? Maybe some power tubes are going bad or the bias is too high.
need help with impedance on SF power 2
I just get a Sonic Frontier power 2 and Genesis APM-1. On the manu, APM-1 impedance is 4 ohms and I am not sure what is the normal impedance for power 2. Is all SF power amp @ 8 ohms. I read on the manu said I have to make sure impedance match with speaker. What effect if I have 8 ohms on the amp and 4 ohms on the speaker? I felt like I need to turn up the volume quite high in order to get a good sound level. BTW, the APM-1 is 90db sensitivity.