Atma-Sphere S 30 & Zero Autotransformer Boxes

Low efficiency? Yes, I think the S-30 is going to run out of gas. There's no way to solve this other than be using a different amp or different speakers.

Agree, to solve the low impedance problem, the autoformers will do the trick. To solve the low efficiency problem, you need more watts.

I had a very early production S-30 and it was definitely load sensitive. It sounded great with my Merlin VSMs, but absolutely wilted when driving my Verity P/Es. I understand (from a post in this forum by Ralph, IIRC) that Atmasphere subsequently modified the design and that later production was more robust. So, I'd be careful re the S-30 if you're looking at the used market.

Marty

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.

Wilsynet and Clio09,
John Atkinson's measurements of my Joseph Audio Pulsars stated: "However, as indicated by its plot of impedance magnitude and electrical phase against frequency (fig.1), the Pulsar is an easy load for the partnering amplifier to drive. Not only is the phase angle relatively low, the impedance remains above 8 ohms for most of the audioband, dropping below that value only in the lower midrange, to reach a minimum magnitude of 6.5 ohms at 210Hz."

Here is a link to those measurements:

http://www.stereophile.com/content/joseph-audio-pulsar-loudspeaker-measurements

Wilsynet and Clio09,
Thank you for your informative posts. The speakers are 8 ohm with an impedance curve no lower than 6.5 ohms. Do you think the Zero Autotransformer will solve the problem? I do not listen to unreasonably loud music since my hearing is very sensitive. I am uncomfortable with the high volume levels that others are often able to tolerate.