Passive feedback looper

[kitschead]

Hi all. I just built a passive feedback looper and it's awesome when I'm using it with my delay pedal. I seem to be encountering some problems though when I want to use it with my bazz fuss distortion pedal or my compression pedal and I'm trying to understand what the reason for this is.
As I turn up the 'feedback amount' pot the signal level starts to totally drop. Is this a commonly understood limitation with passive feedback loopers? I was wondering if its got something to do with the output being loaded down? As I understand it its not possible to simply connect two signals together in parallel in order to mix them as their impedance is too high?
Would it be necessary for me to connect some resistors to the the dry input as well as the 'return' jack in a similar manner to this passive mixer schematic?
http://www.beavisaudio.com/techpages/Pots/PassiveMixer.gif
I'm just trying to wrap my head around the logic of what's happening so any guidance or advice would be greatly appreciated.
Thanks

[kitschead]

Another thought. All the schematics I've seen tend to call for a 500k pot. The pot I used was significantly less than that, I'm not home now so I can't recall what it was exactly.
But is there any chance this could have an effect?

[GibsonGM]

I'm not entirely sure what you have going on, but I bet THIS HERE:  http://www.diystompboxes.com/smfforum/index.php?topic=106805.0  is related to it.

Some sort of impedance issue, most likely.  There is only so far one can go with the passive mixing thing....I would definitely up the value of the pots!  A 1/2 value pot will only provide 1/2 the impedance the circuit needs, in other words...allowing a lot of signal to drain away.      If you just can't get what you want this way, I'd suggest trying out an ACTIVE mixer!  Also called a "summer".  Easy and you have much more control over what is going on...

[nocentelli]

I wonder if it is to do with the fact the bazz fuss inverts the signal at output - You would be feeding inverted signal back to mix with the non-inverted signal, presumably causing cancellation. The fact you get more signal loss as the feedback is increased seems to suggest this.

[kitschead]

After doing more reading I actually just came to that same conclusion that its likely due to the phase inversion of the pedal. I'd really like to be able to use this looper pedal with a whole array of different pedals so I'm considering building some sort of stand alone unit which can invert the phase back again to avoid cancellation.
That way I could theoretically connect a huge line of pedals up and if the phase happened to be inverted by the end of the signal chain I could simply flip it back again.
Does anyone have any experience with this?

[nocentelli]

Maybe something like this:

http://www.doepfer.de/DIY/amp_inv.gif

Make the resistors 100k, and put it on a bypass toggle switch in the feedback path.