Atma-sphere S-30 with Reference 3A?

I've never used the Speltz autoformers and can't speak to their effect on output power with impedance changes.

However the previous statement "Raising the impedance will also reduce the amplifier's power output" is incorrect with Atma-Sphere amps.

In fact just the opposite is true. The S-30 outputs 45WPC into a 16 ohm load and 60WPC into a 30 ohm load.

I think an amp that might work well if there is a lot of impedance swings in the speaker would be the Pass XA30.5, which also happens to be one of the best amps I've ever heard with my Merlins, although If you believe Ralph Karsten (why woulnd't you?)all amps will work better into flat impedances, the higher the better. I don't if it is always true, but my impression is that speakers with impedance swings are best handled by SS amps.

If memmory serves, I believe that the speaker has a relatively benign impedence curve (I investigated the question when I bought them - more than a few years ago). I suspect that the problem with the S-30 may be more a simple lack of grunt. I'm no headbanger, but as spl went up (to modestly loud levels), the S-30 sounded thinner on bottom with the deCapo.
There were 2 reasons I ultimately sold the amp:

The first was that it worked best with horns (Zingali in my case) and I chose to keep my Cary 300b monos for that application.

The second was that IMHO the deCapos were skillfully designed to present a natural octave to octave balance - the low end limitations were matched with a slightly rolled top. (I always felt that they were a great dynamic alternative to Quads). In the end, those limitations were more than I cared for so I sold both amp and speaker. But the main point is, I don't think any amp is likely to change this basic characteristic of the deCapo.

Marty

Well said Marty. Sean, what does the commentary do for your "upgrade" plans?