#1
Guys,
This is what I want to do. I want to split my guitar signal output and run one through my multi-effects unit and other directly to my Blackstar amp's guitar input.
Multieffect unit output is like a headphone jack that will go to the mp3 input of my amp.

So idea is that I can use say acoustic sim effect signal from multi effects unit mixed with, regular guitar amp (clean channel with reverb/delay etc.) signal.

I think it will need a good ABY box; but not sure.
https://www.andertons.co.uk/p/BIGSHOTABY/aby-and-switchers/radial-tonebone-bigshot-true-bypass-aby-pedal?LGWCODE=BIGSHOTABY;56375;6335&gclid=CILv5sOP6tICFQq3Gwodrq0EHA


Is ABY box the right solution?

Thanks
Sam
#2
a/b means one or the other not both together so right there that might present a problem. you also may have issues balancing the 2 signals 


OOPS was thinking Y cord so Roc is right. my bad
#3
The "Y" option on A/B/Y boxes is both signals together, so the answer above is wrong. If you're not concerned with actually switching each output individually you can just use a Y-cable or Y-splitter, which is what the "Y" in A/B/Y is for. A Y-splitter is much cheaper than a pedal so you can at least try your idea out in case it sounds crappy, but of course you might have issues with noise and phase that could be corrected with that ABY pedal. I'd try the splitter first just to test the waters, but it's your money.

I suspect this isn't going to sound great but it will physically send both signals to where you want them to go. You can balance using the output level from the multi effects, that shouldn't be a big deal. 
#4
What kind of multi effects unit are you using? If your amp and your multi both have effects loops you could always hook it up via 4 cable method and not have to use the aby pedal at all.
#5
An A/B/Y box will definitely split your guitar signal, but just bear in mind that if it's not transformer isolated it will physically connect both electrical devices which can cause a ground loop (noise). Also it's not a bad idea to try and find an active splitter, because splitting  an unbalanced line signal will affect the tone.

Whatever box you end up getting, just make sure you do your research and understand if it ticks these two boxes.

PS: Basically an ABY switch is designed with switching in mind, so if you're just looking to split your signal, a cheap and easy way to do this is with a Boss TU3, or similar tuner with a bypass out. I did this on for a whole tour once running into a vox and a marshall with no real memorably bad side effects.
'66 Fender Bassman, '82 Marshall JCM800 4210, '86 Laney AOR 100, '90 Marshall JCM900 MKIII 2500, '97 Marshall JCM600, Silverface Mesa Dual Rectifier, Peavey 6505, Marshall JCM2000 DSL-100, VOX AC30CCH, Marshall JMP-1 + EL34 50/50
#6
BillyEatWorld Thanks for the suggestions. The link I put in my post about BIGSHOT ABY indeed covers those 2 points you mentioned.
Looked at Boss TU3 price and see only £12 difference. SO will go with BIGSHOT ABY.

randefahey Mine is a boss BR80. I didn't know what 4 cable method was. Googled up and sounds pretty decent but I neither have the MultiX unit nor the amp that has all those effects loop.
#9
PSimonR Good audio transformers are expensive man. Youd be surprised at how much signal you lose through a transformer so it means you generally have to use really good quality ones to avoid a huge difference in tone. 

Ive actually looked in to building my own clones of radial style Di boxes and gave up. It's not worth it by the time you buy all the components and the transformer. I'd say the same thing applies to the ABY switch the OP linked as it's also made by radial.
'66 Fender Bassman, '82 Marshall JCM800 4210, '86 Laney AOR 100, '90 Marshall JCM900 MKIII 2500, '97 Marshall JCM600, Silverface Mesa Dual Rectifier, Peavey 6505, Marshall JCM2000 DSL-100, VOX AC30CCH, Marshall JMP-1 + EL34 50/50
#10
Yeah, it would be hard to find a decent ABY with an iso transformer and phase correction for less than that. If there is one, I want to know about it. 

Simple passive ABY pedals are common enough but some rigs benefit a lot from those extra features. At the very least, the iso out is nearly always quieter when running a pedal chain into one amp.