Multi-stage mixer (for want of a better term)

[niftyprose]

Hi guys, I'm unlurking with an open-ended question.

I'm building a performance-oriented pedalboard with the minimum number of boxes. My requirements are a bit unusual and I'll leave out the boring detail. Upshot is that I'm dealing with three and possibly four signals, all ultimately originating from me and my sort-of-guitar.

Obvs. a three- or four-channel active mixer is the way to go. SInce I'll likely be building it myself, I figured I could add TRS jacks between the inputs and the corresponding channel pots allowing me to easily connect effects as needed with the mixer as nerve centre. (So I'd have eg my Pearl AD08 on one of these : https://www.thomann.de/gb/cordial_cfy_09_vpp.htm?sid=eed15fbf6a299c89a4fba18df9dfbdad and plug it in to channel #1, 2, 3 or 4 as needed with just one jack.)

So far so good. However, it then struck me that (again in abstract terms) I might find myself wanting to mix channels #1+2 and then apply an effect to both of them after mixing. So I'd mix 1+2 and then run the output through another TRS jack, enabling me to assign the AD08 to ch#1, 2 or 1+2.

Here's a really terrible diagram of three channels. X marks TRS jacks, > marks interchannel junctions

1--x--\
          >--x--\
2--x--/          \
                    >--x--
                 /
3--x--------/

As far as I can tell no-one else is doing this stuff. The objection I  can see is that I'd need a separate op-amp for each > but that doesn't look like much of a problem. Can anyone point me at a suitable resource for calculating gains and such or am I totally off-beam?


Best, NP

[PRR]

> no-one else is doing this stuff.

Large (analog) recording consoles are full of this stuff. Inputs have insert points and are switched to sub-buses. Subs may have inserts and are then mixed to main buses, or into other sub-buses.

It's just building-blocks.

[niftyprose]

Ah, right, sorry, I meant in pedal or pedal-like format. Thanks for pointing me at consoles. Is it the case that in my crap diagram I could have three op amps of the same type, or is there some formula for choosing gains and so on? Best NP

[PRR]

Use unity-gain mixing, until you prove a stage "must" have gain. Then it is just a resistor change.

[niftyprose]

Thanks, PRR! Best, NP