Passive splitter/blender with feedback problems

[jackalkirk]

Need help.  I have designed a very simple passive blender pedal that splits an input signal to an output jack and to an effects loop path that is routed back to the output jack.  I simply connected all the grounds together.  Didn't ground to enclosure itself.  I have the potentiometer set in the input to output signal path (seemed to work better than in the effects path).  Plug in a RAT distortion pedal in the effects path and I get some feedback with potentiometer wide open but, a little bit of resistance (turn of the pot) and the feedback goes away.  So, thats good.  However, if i plug in a phaser, i get lots of strange feedback no matter where the pot is set.  Can I overcome this with a passive design?  I am hesistant to learn how to make active pedals.  I tried a germanium diode, thinking the one-way aspect of these things would do the trick, but doesn't help.  I am also hesitant to put any resistance in the effects path as resistance in both paths would lead to volume drop.  Any suggestions??  Thank you.

[PRR]

> Didn't ground to enclosure itself.

Why not? Takes 3 seconds to try.

> I tried a germanium diode, thinking the one-way aspect

Audio swings both ways. At best you have distorted feedback.

> lots of strange feedback no matter where the pot is set.  Can I overcome this with a passive design?

Not for all cases.

It isn't what "kind" of box comes in front. It is whether its output impedance is low enough to absorb the sneak-path through the blend pot. The for-sure cure is an active buffer or an active mixer.