I know this comment is not exactly responsive to your question, but I can't resist. In the late 1980's I bought the first version of the ARC SP-9, and it was the first really "serious" preamp I owned. What a MAJOR disappointment it proved to be. After all the glowing reviews of this preamp in the major audio journals, I really expected a significant improvement in my system. WRONG!! From that time forward, I have always read reviews in the hi-end audio publications with a very healthy dose of skepticism (particularly reviews of ARC's product line).
I kept the SP-9 for about 6 months, hoping that some other equipment changes in my system would let it show its stuff, but it never happened. The Mk2 of the SP-9 version may have been better, but by then ARC had lost me as a customer. Your post does not indicate the reason behind your question, but if, by some chance, you are considering the purchase of any of the SP-9's, I would strongly advise you to buy something else. There are many tube preamps, and even many solid state preamps, that run rings around the SP-9.
I kept the SP-9 for about 6 months, hoping that some other equipment changes in my system would let it show its stuff, but it never happened. The Mk2 of the SP-9 version may have been better, but by then ARC had lost me as a customer. Your post does not indicate the reason behind your question, but if, by some chance, you are considering the purchase of any of the SP-9's, I would strongly advise you to buy something else. There are many tube preamps, and even many solid state preamps, that run rings around the SP-9.