Mix multiple audio signals together from TRS cables

Question

I have a drum machine that gives out separate outputs for each one of its 11 sounds. I've found that I don't really need 11 outputs and some of these can be grouped, e.g one signal that has the low/mid/high toms. So I was looking for a device that would take in multiple mono TS/TRS inputs and give one output that's the summation of these inputs. I had assumed that this will be a simple cheap device - a voltage adder basically - however, such a thing doesn't seem to exist so I may be missing some understanding here.

So my questions is if this can be done, then what are the options? Using an audio interface/mixer and outputting the mix signal is an option of course, but the whole point of this is to mix the signal before it reaches the interface.

If this is not as simple as it sounds which explains why there is no such device around, then could you explain why?

Thanks!

Answer 1

What you want to do is to mix signals, so you need a mixer.

Perhaps the cheapest and simplest commercial device to do the task could be a passive mixer. Note that passive mixer will reduce the signal volume so you will need to compensate for this either by increasing the output volume for the mixed channels on the drum machine, or input gain on your main mixer.

If you're into electronics and soldering, you could try to make one yourself, see e.g. this simple diagram:

https://en.wikipedia.org/wiki/Electronic_mixer

Alternatively, there are also simple and cheap active mixers in the market.