A/B/C switch

[MBackus]

Hello!  I'm brand new to building pedals.  Built the beginners project on here, big muff clone from GGG, and a true bypass/feedback loop from EACED.  My next project I am working on is an A B C switch for a friend.  But he doesn't want the stand two switch (A and B or C, B or C), he wants to be able to play all three at once,  (guitar, two synths).  So I started working on it.  I just need some guidance from some more experienced people.  How am I looking so far?  And do you think this is a good approach for this idea?

[MBackus]

[Leston Braun]

I'd try the AMZ Splitter, just build the three-way splitter, and then add switches to ground the outputs, and turn on the LEDs. With your plan the following inputs will load eachother and probably cause issues.

http://www.muzique.com/lab/splitter.htm


Edit. Oh, I just noticed that you want to drive three different signals into one amp at the same time (and not one signal into three amps..)? Then the Splitter won't help, I think you need some kind of a mixer to do that. Or something else beyond my wisdom.. 

[Processaurus]

Yes, your first design works fine for splitting a signal and fanning it out to three amps (or board, other effects, etc.), but mixing (3) signals down requires more parts, because if outputs are connected directly together, the results are usually bad, the instrument with the lowest output impedance will be louder, because the instruments are "loading" each other, like when crackheads plug a couple amps into one speaker cabinet.  To stop the outputs from interacting with each other, you need some electronics between them, a mixer.  The simplest mixer is a passive, resistive mixer, that runs each input to a series resistor (10K will work often), and then ties all of the free resistor ends to the output.  That works by making it so an input has to go through 2 resistors to see (be loaded by) the impedance of the other inputs, but only has  to go through 1 to get to the output.  This works, but will eat some signal, and you'd want active electronics from each instrument feeding it (no guitars plugged straight in).

If the guitars may be connected directly, you'll want to buffer them before the mixing stage.

[Processaurus]

Oh, on your second design, you'd want a separate resistor for each LED, or one will be brighter than the others because with diodes in parallel, one turns on at a little lower voltage than another.  Look up "diode current hogging".

[MBackus]

yeah... After looking at that set up for a while, I realized something just wouldn't work right.  The three signals wouldn't mix well *that* easy.  So I came across this simple three channel mixer from Experimentalists Anonymous.  But what about the passive weak signal from the guitar??  He's going to be playing guitar mostly, and the keys just a bit.  The one resistor for the three leds was something I was really unsure about.  But, I'm really new to building circuits, so I figured I would give it a go and quickly be corrected. 
  So I've been looking at this schematic, drawing it out on paper, adding a dpdt switch before each of the potentiometers?? I'm thinking this might sound find with the synths, having some sort of active power behind it.  What would your advice be?  I mean if it gets too complicated its obvious to just switch to a a/b/y switch.  But if I might be on the right path, I would love to figure it out.N00b

[MBackus]

*bump*

[Processaurus]

A buffer between the guitar and the in on that mixer would make it sound right (as the buffer would better drive the 10K load from the pot better than the guitar's pickups).  I like discrete FET buffer at GGG.  A while ago I pitched this simple buffered 4 channel mixer too, which could easily be paired down to three if you needed something like that.

http://www.diystompboxes.com/smfforum/index.php?topic=54816.0

[MBackus]

Okay.  I'm unfortunately working doubles galore this weekend.  Can't wait to find some time to look over these schematics.  So you don't think adding a buffer that early in the guitar signal will be bad? 
Michael.