Preventing Feedback in Multi-out circuits

[Danbieranowski]

I've put together this kind of overly-ambitious build for my experience level, which is 3 "pedals" in one enclosure with individual outs and a summed out (it's an input into a Zapper which splits to a Rat and a Muff, so a single input, a Rat out, a Muff out, and a summed out of the Rat and Muff). All 3 pedals work, and the individual outs as well as the summed out work. The problem is there's feedback occurring within the circuit. The only time it doesn't occur is via the summed out with all 3 pedals active or if I turn the volume knobs on the Rat and Muff super low.

You can hear the circuit in the video below (which sounds awesome and thiccccc), and you can hear the feedback in the last 10 seconds of the video:

I used @Ratimus suggestion for simple wiring via resistors (47k - see below) to isolate the Rat out and Muff out from the summed out so that I don't get the same signal on all 3 outputs, and this does work... I don't get much Muff bleed into the Rat out or much Rat bleed into the Muff out. The problem is if I push volume above say 10% on either the Rat or Muff I get feedback on the individual outputs (Rat out and Muff out). I don't get this loop on the summed output if all 3 pedals are active or inactive though.

Anyone have any ideas?

This is the wiring diagram I went with that Mr. Ratimus drew up.

 

[Danbieranowski]

Some additional notes:
1) The Zapper (the pedal in the middle) doesn't cause any feedback. It's only the Muff and the Rat. If both are turned on, there is no feedback. If one is turned off, there is feedback. So when I said all 3 pedals have to be on to remove the feedback, that isn't true. Only the Muff and Rat have to be on. If either is off, the feedback occurs on all 3 outputs. If both are on there doesn't appear to be a feedback problem on any of the 3 outputs.

2) As I turn the volume knob, the oscillating frequency of the feedback changes. So if I turn it up the feedback will go higher or lower in note.

 

[Danbieranowski]

I’m wondering if this would work as an answer. Taking the out of the Zapper into this and splitting with one out to the fuzz, one out to the rat, but returning both back to the board for a blended out.

https://guitarpcb.com/wp-content/uploads/2018/06/BD_ParaMix.pdf

 

[zgrav]

I imagine the mixer board would solve your issue, at the expense of turning your 3 in 1 to a 2 in 1, plus a lot more electronics. If you wanted to go that route I would suggest going way over the top and build a VFE Klein Bottle as a separate project. But for your project at hand I think you have more options to try that are simpler, like treating all the outputs as part of a passive mixer.

look for some ideas here: http://www.runoffgroove.com/splitter-blend.html

and the discussion here with R.G. Keen about his passive mini-mixer design: https://www.diystompboxes.com/smfforum/index.php?topic=117976.0

 

[Danbieranowski]

I imagine the mixer board would solve your issue, at the expense of turning your 3 in 1 to a 2 in 1, plus a lot more electronics. If you wanted to go that route I would suggest going way over the top and build a VFE Klein Bottle as a separate project. But for your project at hand I think you have more options to try that are simpler, like treating all the outputs as part of a passive mixer.

look for some ideas here: http://www.runoffgroove.com/splitter-blend.html

and the discussion here with R.G. Keen about his passive mini-mixer design: https://www.diystompboxes.com/smfforum/index.php?topic=117976.0

I’ll dive into these today. Thank you as always!

 

[Danbieranowski]

If anyone is curious, I managed to resolve this issue by going directly out of the fuzz and distortion circuits into this tiny “mini mixer” board: http://www.generalguitargadgets.com/effects-projects/boosters/mini-mixer/.

So the signal flow goes into the EQ/Boost, then it gets split off the OUT of the 3pdt board to the IN of both the Rat and the Muff. The Rat goes to its own output as well as one of the IN channels on the Mini-Mixer. The Muff goes to its own output as well as one of the other IN channels on the Mini-Mixer. I used internal trim pots on the Mini-Mixer, and used its output to a summed output where the Muff and Rat get parallel combined.

The 3 outputs are Rat out, Muff out, and summed out.

Here’s how it sounds:

Leaving this thread up for anyone who googles this type of issue!