UST plus mag
 

Question. I have a ust pickup on my guitar, and am considering installing a mag as well. Both the ust and mag have onboard volume controls. I'd like to experiment with using them both simultaneously.
But only want to take up one channel in my acoustic amp. What if I took both those cables and ran them into the stereo inputs of my reverb (or delay) pedal, then ran a mono out?
Is that too simple a solution? I don't have the mag yet or I'd try it, but just asking the question. Thanks!

it might work

It probably won't work because of the variation in impedance between the pickups. Ideally you will need a twin channel preamp which can blend the sources.

Cut and pasted from another thread, here's a list of contenders:

Grace Design Felix (Gain and EQ on both chans) = $1000
K&K Quantum Blender (Gain and EQ on both chans) = $352
K&K Dual Channel Pro (Uses one TRS, Gain and EQ on both chans - need to unscrew the box) = $150
Red Eye Twin (Gain and "simple tone control" on both chans) = $300
Headway EDB-2 (Gain on both channels, EQ only on sum) =$365
LR Baggs Mixpro (Uses one TRS, Gain on both chans, adjust low cut on the ring side, No XLR out) = $170
Radial Tonebone PZ-Pre (Gain on both channels, EQ only on sum) = $300
UltraSound DI Max Stereo (Gain and EQ on both chans) = $150
D-TAR Solstice (Gain and EQ on both chans) = $350
Fishman Pocket Blender

Since both have volume controls to tweak the balance, I don't think the impedance mismatch is material going into independent active inputs on a stereo effect. A bigger problem will be if they are not in-phase with each other, which should be a simple test into any amp or PA using two inputs.

I did a similar setup with piezo on the ring and mag on the tip of s TRS jack. I can either use a TRS cord going to a splitter then send the tip to one channel of my Carvin and the ring to another, OR run both to my Baggs Mixpro. You can't simply combine the two signals - it won't work.

I bought a Masterbilt Epiphone DR-500mce largely because of it's magnetic / undersaddle pickup combination. The blended sound is perfect for my jazzy pop fingerstyle playing. I recommend this approach regardless of how you achieve it equipment-wise.

One thing I had to do was change they type of strings I use. I had been using Elixers for years, but I found they were too soft through the magnetic pickup. Coated D'Adderios give me a much better blend between the two pickups. With a custom system, you probably will have more flexibility in terms of boosting the output from the magnetic pickup, but it still might be something to consider.

Generally speaking with stereo effects when both inputs are plugged in the outputs correlate on a 1:1 basis with the inputs. Meaning right out only passes right in and left out only passes left in. If you want a fairly simple blender option for two pickups, Radial makes a nice compact little pedal called the mix-blender which lets you individually blend the level of each pickup into a mono output. It also has an fx loop that is independently blendable.

Tldr; I don't know of any stereo effect that will do what you're looking for.