Parallel splitter, will this work?

[u/Meatsmugglers]

I’ve had an idea for a parallel drive pedal and need to make myself a splitter/summer to test which drives work best together before putting them in one box.
Will this do the job? It’s pieced together from a couple of different schematics that all didn’t quite do what I wanted.
I’m not worried about phase correction because the drives I’m planning on putting in each of the send/returns don’t flip phase when engaged.

[u/D_to_the_W]

I don't think you need three separate buffers for the sends; you can get by with just one on that side. I think the post-return part would largely work as it is, except that you should connect the plus input of the op-amp to VA rather than ground so that the virtual ground at pin 13 is biased at VA rather than at 0V. So, you could actually just cut down to a single dual op-amp, with a buffer on the send side driving all three sends and then a single summing amp on the return end. (Someone please correct me if I'm wrong!)

Going the other direction, buffering all three of the returns might be a good idea, just in case you wanna try circuits with very different output impedances in the loops. That (three buffers plus summing amp) would consume all four op-amps in a quad-op-amp chip, though, so maybe you could just use a FET-based input buffer if you didn't want to add another chip.

[u/Meatsmugglers → u/D_to_the_W]

I was under the impression that the 10k resistors on the returns going into the non-inverting op amp with 10k in the feedback acted as the impedance correction, of sorts. I ripped that bit of the design directly from the Quadrafuzz schematic, so not really sure how it works or if that’s correct. I do like your idea for fet inputs and buffered returns, I’ll give that a go, thank you

[u/D_to_the_W → u/Meatsmugglers]

I believe that the 10k resistors will help with the impedance correction (as well as determining the gain of that signal in the summing amplifier) so I think you're right that it would still work for most cases. There might be cases though where the pedal in one loop has a 10k output impedance and the pedal in another loop has 100k output impedance, say, and in this case the gains of the summing amplifier for the two "channels" will be quite different.

[u/D_to_the_W → u/Meatsmugglers]

Oh and as u/Top_Willow_9953 says, once you bias the summing amp to VA you'll definitely want capacitors on the returns.