Mono-Stereo Junction Box Build Problem

[JCGH]

Hi all,

I was wondering if someone could help me as I'm still fairly new to this. I'll try and explain the problem without making it too confusing...

I'm building a junction box for a friend which works as follows:

Input > True Bypass Switchable Buffer > Send (to pedals)

(From pedals) Return R + Return L > 470R MF Resistors > SPST Mono-Stereo switch > Out R + Out L

The Input > Send works just fine. However, I'm having trouble getting the second part to work.

The Return R > Out R works fine when the switch is in the one position (I can't remember which one, I believe it's stereo) but not in the other, let's assume it's mono.

The Return L > Out L does not work whichever way the switch is and after an audio probe test I have found that the signal even at the tip of the cable is significantly reduced compared to that at R Return, which I do not understand!

I tried it out in reverse as well (as in I plugged the guitar into out and the amp into return) and the same thing happened...

I'm not sure whether it's something to do with ground? Currently, all the jacks + buffer + buffer switch are ground together; should I separate the grounds of the Input > Send and the Returns > Outs?

Any help will be much appreciated! Cheers.

[Transmogrifox]

A diagram would help so we can see how the SPST stereo/mono switch is (or isn't) working.  Are you just switching the Left (mono) output between L return and the center tap between the 2x470R?

470R is a pretty low value for most stompboxes to drive.  You probably want your stereo-mono "mix" resistors on the order of 470K (1000 times larger value).

Then after that you may want to (at the very least) use a JFET buffer, and better would be a booster for gain recovery.

Grounds should all be tied together.