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400 Space-Expander conversion

kappclark

kappclark

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Looking for a link to see what is involved in converting the space-expander jacks to "pre-OUT" "main IN" jacks... The fabulous threads on improving the 400 , and the stickies make mention of this mod, but I cannot see exactly what is involved .. right now am using the aux line-in to receive the output of a SS preamp..gives me remote control capability..
 
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Did that with a redesigned 600-T. With a 400, there might be impedance issues to deal with.

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Its in one of the threads but I believe it involves use of an op amp wired as a zero-gain buffer to deal with the impedance issues. Stock the output of the line stage doesn't have much drive capability so the op amp is required to sort that out.

have this schematic saved from one of the 400 threads, but which one and what other fine points I do not know.
 

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I've seen the unity gain mod in a few threads. Thorne did one for his 500C. He had some struggles with it, but pretty sure he sorted it out. Might want to check with Thorne on his experience.
 
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