need help with impedance on SF power 2

If you have the manual, just follow the instructions for load impedance adjustment. Ideally, if your APM-1 is rated 4 ohm, then the Power 2 should also be set at 4 ohm. Won't hurt to experiment, however, it's not like changing cables from terminal to terminal...you gotta' go under the 120lb amp and remove all them SCREWS!!

Thanks, I am going to try it. BTW, is the SF power 2 is OTL or it will alway keep the same power output(110w) in 2, 4 or 8. Which means, even I drop the ohms to 4, I still get 110w (not higher). Will that drop make the amp run not as stable or sound not as good?

The power will not drop, and the amp will work easier set at 4 ohms, thereby prolonging the life of your tubes.

I've been using a power 2 SE happily for a year now. I've used them with ML Aerius i's and PSB Gold i's. I found that these "4 ohm" speakers sound much better off of the 8 ohm taps. The bass isn't as tight but everything else is much improved i.e.. soundstage depth and width, separation et al. Try it for yourself. I know, it is a pain in the butt removing all of those screws though.....

How could you have purchased a tube amp without knowing it had output transformers? If you didn't know this, I recommend you carefully read the owners manual before you attempt to operate this or any tube amp. SF products have some of best manuals in the industry. If you didn't get one with amp, you can download it off their the website.

Agree with Gsselling, what you give up in bass control on the 8 ohm tap, is more than made up for in openness. You can tighten up the bass by replacing the stock 6550s with KT-90s. Talk with Kevin at Upscale Audio.