Audiophilepure

https://pt.audio/2025/06/08/atma-sphere-gem-integrated-headphone-amplifier-review/

What I have here is a really tiny amplifier. Actually, it’s way more than that; this gem really does duty as an integrated amplifier that can handle both efficient speakers and a bevy of headphones, ranging from the efficient to the not-so efficient. I’m not really much of a headphone guy, so I employed this Gem as an amplifier for my really efficient Charney Audio Maestro-X single-driver speakers.

A bit of history about Atma-Sphere first. Ralph is best known in the industry for pioneering two things: output transformer-less (OTL) vacuum tube amps and use of fully balanced circuitry and connections in his amp and preamp products, and these design elements are highlighted in his mainline designs to this day. Interestingly, the Gem (on the surface… see below) sports neither. Right on top are exposed output transformers, and a quick look at the rear panel indicates the presence of (only) single-ended RCA input jacks. Was Mr. Karsten perhaps being a bit contrarian here with this design?

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