4x4 passive matrix mixer

by **Glace_Noire** » Tue Nov 10, 2015 6:34 pm

I plan to build a 4x4 passive matrix mixer, but I failed to find a proper schematic on the internet since everyone seems to use different pots or resistors value
Is anyone here who already did something similar?
Is the guitar signal will be divide between each output and so it will lose some gain to "attack" the pedalboard and/or the amp according to my plan?

by **crochambeau** » Tue Nov 10, 2015 6:41 pm

I think you'll want a more or less standard level at the inputs, based on my (potentially errant) guess that your contact mic and guitar are plugging direct, you're going to essentially lose them in the face of the Volca and pedal board.

I'm awash in deja vu right now though, maybe I need to access the thread somewhere that reminds me of this, and get firmer footing.

by **Glace_Noire** » Tue Nov 10, 2015 6:50 pm

Thanks for your help dude!
You're right: I plan to plug my guitar and contact mic direct in the mixer.
And so I roll back the volca and pedalboard feedback loop pots, do you think I could have an acceptable balance between output levels?

by **crochambeau** » Tue Nov 10, 2015 7:53 pm

You could balance it, but I would expect you'll be ahead if you put a boost/buffer on those two. In my experience, highly disparate signal types don't lend themselves well to passive combination, though to be fair I haven't climbed aboard the matrix mixer train. Upside is: you can simply build the matrix mixer and add those parts externally if needed.

Regarding actual schematic, often times the end value is not critical, or benefits from being scaled up or down depending on how many channels you're building and the type of signal you expect to see at input.

Given a four channel, you're going to have four of the pots IN PARALLEL loading down each input, so... if you grab a 100K pot the branch load at input will be 25K. Most everything active will be happy with this value, your guitar might shit out a lot of the top end (solved via a buffer, so let's pretend that's not a huge concern) and I tend to gravitate toward 10K as a mix buss resistor, though you'll get a fair amount of crosstalk with hot signals.

In my mind, that covers it, though if you have anything +/- 50% in value you'll have similar results would be my guess.

I can dig up a drawing if there's confusion still afoot...