Atma-Sphere S 30 & Zero Autotransformer Boxes

I have used mine with a pair of Spendor 3/1 and Maggie 1.6QR speakers. My business partner had a set of autoformers lying around that he made up a while back that are a 1:2 ratio. So essentially it doubled the impedance of the speaker. The amp sounded fine with the Spendor's even without the autoformer, but the autoformer did help IMO. Especially when I pushed the sound level up over 90 SPL which is kind of rare for me. As for the Maggie's, it would have helped to have a 1:4 ratio on the autoformer. Better yet a pair of M-60's and the autoformer would have been better.

A lot will depend on the impedance curve of your speaker and how loud you plan to listen. The Atma-Sphere S-30 will put out more power into higher impedances, but after 32 ohms power will drop. So you really need to understand the entire impedance curve of your speaker.

Looking at the graph from the Stereophile review the impedance curve has a couple spikes in the bass region under 100 Hz. Other than that it is quite smooth. Using a 1:2 ratio on the autoformer would mean that the S-30 power would be around 45 watts for the most part. Those two spikes notwithstanding which appear to be just over 20 ohms. So at those points you might get slightly less than 45 watts, but at moderate listening levels should be just fine. Probably no different than my experience with my Spendor's.

My advice would be to try it standalone first and see how the amp fares. I think you might be fine. If you feel more power is needed then you can try the autoformers. If you live in the US and would like to try my set then contact me offline and maybe we can arrange for you to borrow them.