I was just curious, for this amplifier, how extreme can I go with R1? (what is the maximum value of R1?) I'm curious. Would omitting R2 produce any negative effects in terms of input sensitivity? My Q1 in this case is a Pn3563 with a measured HFE of about 130. I find that a high R1 increases distortion, and a low R1 reduces sensitivity. Please tell me what you suggest for R1 and why.