OK, technical time. In another thread regarding summing amp modules, the topic of "passive summing" circuits came up. I have encountered this a few times recently and my lack of electronics education has resulted in major confusion. Can anybody explain the following problem to us non-techies?

I just don't understand the difference between these two methods: in the "active" summing method, multiple inputs are summed and amplified; in the “passive” circuit, the inputs are summed and then fed into a "make-up" gain amp. What's the difference? Any recommended sources for enlightenment? Books, magazine articles, meditation? Thanks.

steve
sjp@pacbell.net