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OTL, Output Transformerless Amplifier User Group.

RE: M60

This Asylum is a descendant of the "Atma-sphere Owners Group", aka "ASOG". If you search on that title, you might find an archive with Speltz's tweaks. I know I could find it 4-5 years ago, when last I looked for it. Further to that, you can contact Paul Speltz the man; he is the proprietor of "Anti-Cables" a thriving internet business located in Minnesota. Paul is a very nice guy, and he may be willing to forward to you the info.

One tweak that I remember well, because I use it, is to insert very small value resistors between the capacitors in the LV power supplies to the output stage. Thus you convert what was a pure capacitor filter into a CRC filter. For all I know, that practice may be standard now for Atma-sphere. The end result was a CRCRC or CRCRCRC filter, where the first R was 0.5 ohms, the second R was 0.21 ohms, etc. Each C was about 2000uF, with a much higher amount of C at the last stage. Another tweak was to convert the Cathode Follower driver stage to a version of late Allen Wright's "Super Linear Cathode Follower" (SLCF). That's described in AW's "Preamp Cookbook". But Paul had a schematic that suits the Atma-sphere topology.


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