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DIY For Audio
DIY Precision fidelity C7A
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<blockquote data-quote="handsome" data-source="post: 1081420" data-attributes="member: 772"><p>That circuit has a constant-current loaded cascode (LOT of gain) plus another gain stage (even more LOT of gain) plus a constant current loaded cathode follower all wrapped up in a feedback loop that uses very large (12 Meg) resistance - the potential for oscillation is very, very, very large. So physical layout will be paramount. So will your earthing. You will need to consider current paths. None of the tubes bar the input tube, use stoppers. The second gain stage has some high-frequency tailoring that could be part of the phono equalisation or is an attempt to tame oscillations or both. Either you should try and copy the original PCB exactly or be prepared to do a lot of board-making until you get the one that works. Its obviously a worthwhile project but will be a proverbial pain in the proverbial butt to bring to fruition.</p><p></p><p>Sent from my SM-A715F using Tapatalk</p></blockquote><p></p>
[QUOTE="handsome, post: 1081420, member: 772"] That circuit has a constant-current loaded cascode (LOT of gain) plus another gain stage (even more LOT of gain) plus a constant current loaded cathode follower all wrapped up in a feedback loop that uses very large (12 Meg) resistance - the potential for oscillation is very, very, very large. So physical layout will be paramount. So will your earthing. You will need to consider current paths. None of the tubes bar the input tube, use stoppers. The second gain stage has some high-frequency tailoring that could be part of the phono equalisation or is an attempt to tame oscillations or both. Either you should try and copy the original PCB exactly or be prepared to do a lot of board-making until you get the one that works. Its obviously a worthwhile project but will be a proverbial pain in the proverbial butt to bring to fruition. Sent from my SM-A715F using Tapatalk [/QUOTE]
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DIY & Tutorials
DIY For Audio
DIY Precision fidelity C7A
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