ruffrecords said:I am not quite sure exactly what you mean by force the bus low to ameliorate gain changes but they did not slug the bus to do this.
For the most part this is so. But I've worked on quite a few originally built for broadcast small desks where the input to the bus amp was slugged and forced low for this exact purpose. Of course, lots/most (all?) of the bigger recording desks with comprehensive and buffered router modules didn't and, as you say, it was just brought down to the 300 ohm area for the 10468 xnsformer.
Perhaps I should have limited my example to Helios since Dick Swettenham wrote about this technique of forcing the bus low and therefore, it's a more well known example.
P.S. Just in case it wasn't obvious - I'm not advocating using hybrid coils, or parallel plate mixers, or forcing your bus low - I was just chucking in some filler material on the thread.