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OTL Asylum OTL, Output Transformerless Amplifier User Group. |
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OTL Asylum OTL, Output Transformerless Amplifier User Group. |
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In Reply to: Schematics posted by Greg Peters on August 19, 2002 at 05:30:57:
Greg,Welcome to the world of high-end audio. I believe Atma-Sphere amplifiers are the best in conveying the details in sound recordings, and have derived great satisfaction from making my own equipment. You could not find a better way to start than by making your own M-60s.
Unlike Fourier Components, which is out of business and has apparently abandoned its circuit designs, Atma-Sphere is a thriving concern. Ralph Karsten, the proprietor, no longer sells M-60 kits, but still had assembly manuals available for US$7 the last time I heard. This manual contains a schematic. Together with photographs of Atma-Sphere owners' equipment available on this site, and advice freely given by the many users with extensive electronics knowledge and experience, the manual is sufficient to allow you to build a working pair of amplifiers.
Because the circuits are proprietary to Atma-Sphere Music Systems, we will not distribute them. You will have to get a copy from Ralph.
The M-60 power output is rated at 60 watts into 8 ohms and 45 watts into 4 ohms. It is characteristic of OTL amplifiers that they deliver more power into higher impedance loads, and people generally find it is easier to match these amps to higher efficiency, higher impedance speakers. There are autotransformers available to improve the matching to low impedance speakers if you have some you really like. To use autotransformers with OTL amplifiers seems a philosophical contradiction, but the autotransformer design problems are not nearly as severe as those of output transformers found in conventional single-ended triode (SET) or push-pull valve amplifiers. See the Atma-Sphere company web site or Paul Speltz' listings on this site.
The Fourier amps were derived from the original OTL amplifiers built by Futterman. These were notoriously unreliable and have given OTL a bad reputation. The Atma-Sphere amps are designed to be simple and reliable. If you explore this site extensively, you will find tweaks discussed that may trade reliability (and speaker safety) for improved performance. My advice is to stick with the stock amp circuit for your first project, and only worry about these tweaks once you have some experience in building and enjoying the music they create.
Good luck with your project!
-Al
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Follow Ups
- Re: Schematics - Al Sekela 08/19/0209:27:59 08/19/02 (0)
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