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RE: MP Engineering OTL

Without referencing the schematic a second time, a capacitor between the input stage and the driver stage can correctly be called a "coupling capacitor", but when I said there was no output coupling capacitor, I was referring to the interface between the output tubes and the speaker. Thus you need to carefully adjust DC offset before hooking these to a speaker, which I think is why there is a meter placed into the circuit by activating that switch shown above the 3.3R resistor. Counterpoint SA4 and KSS both I think were Futterman designs with no coupling capacitor too. I think Counterpoint used some sort of servo mechanism to keep DC offset low or absent. But both of those amplifiers could occasionally cause problems.

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  Michael Percy Audio  

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