Summing Audio - is it really THAT easy? featuring: MIDIman

[SampleGrinder]

Hey you good people!

I bought a rack mixer called "FineLine" from MIDIman. Must be 90s or so featuring:

10 unbalanced mono line level inputs summing to one "left" output
10 unbalanced mono line level inputs summing to one "right" output

the individual channels habe no controls - no gain, no volume, no EQ - nothing.
All this unit basically does is summing these 20 inputs (there is a volume pot for the "left" & "right" master output sum)

(There are also some mic inputs and some sends, but this is not part of my topic)


I was curious about how this summing is done so I analyzed the circuit board.
What I found was so simple I could not believe it.

Each of these 10 inputs goes through a 4,7uF condensator, then through a resistor and then the inputs are just connected togehter to make the summing. after that all 10 summed signals go in to an op-amp.

I have made some pictures of the circuit if you´d like to see.

My question is:


01: is it really THAT easy to do audio summing?
02: could I make my own summing mixer with as many inputs as I wish using this method?
03: What can be said about this procedure

- is is a good idea doing it in this way
- where are the problems / limitations in this method
- just basically your opinion on this & discussion


would be greatly appreciated!

Thanks - Si