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!!

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.

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.

Thank you, Gsselling & Kana813. The power 2 I got is actually SE version, they use the kt88. If I put it on 8 omh tap, will it shorten the life of the tube?

You are very luckly to get an SE.

Using the 8 ohm tap will not shorten tube life.

Just make sure the tube bias is set correctly, which is very easy to do on SF amps.

If you decide you don't like the amp, please contact me.

I set up every thing today and put the power 2 into 8 phms tap. I also have a line 2 pre amp. However, I felt that i need to turn the volume up to 60-70 (line 2 volume control from 0-95) in order to get a enough volume level. I check the bias and it is right. Did I do some thing wrong? The APM-1 is a 5way speaker. It has its own amp for the 15" woofer. So, the power 2 just need to push two 6", one 5" and two 1". It should not need to push that hard. I am using the trivista as the source. Since the trivista doesn't have the xlr output. I put the RCA to line 2 and from line2 to power2 using the xlr. Will that cause any trouble?

Waip7- I also have a SF Line 2, running a single-ended/RCA
source in and balanced XLR out to the amp is perfectly
fine.

A volume level between 60-70 for loud normal playback
is also fine. I normally listen between 55-65, but my amp's
input sensitivity is lower than the Power 2. It also depends on the output level of the source and the size of your room.