Feedback looper troubleshooting

[pavle]

Hey all,

I'm taking my baby steps into this world. I can sincerely say nothing makes me feel as daft as electronics, but it's probably good to be humbled from time to time  .

I've tried to put together a very simple circuit to start, namely a feedback looper. I've based it on the directions given in this article, specifically this part:

One modification that you can make to this project is removing the true bypass entirely and just having a permanent f/x loop while retaining the ability to turn on or off the feedback circuit. To do this you can completely drop the 3PDT in the schematic and use either a DPDT (if you want an LED) or even just the SPDT if you don’t need an LED. For SPDT, wire the Input to Send, the Output to Return, and the center lug of the SPDT to Send, and one of the side lugs to the center lug of the 500k pot. Lastly wire one of the pot’s side lugs to Return. Now the effects chain will always be on, but the SPDT will toggle whether the feedback loop is on or off.

Here's what I've done, as an illustration:


As it stands, I get my signal passing through the circuit fine (along with effects from the delay/reverb in the loop), but flicking the switch/turning the pot does nothing at all. What have I done wrong?


_____
Edit: Corrected illustration - there is no wire connecting send and return.

[FiveseveN]

Hello and welcome!
Jacks have at least two pins:

Your illustration suggests you've only connected the Sleeve pins, but I doubt that was the intention. Did you mean to represent the Tips and are the sleeves connected together?

[pavle]

My bad: the diagram is only showing the tip connections. I have connected the sleeves of the 4 jacks together for grounding. I haven't soldered anything else to the sleeves.

[iainpunk]

you are trying to directly mix two high impedance signals without current limiting resistors? seems odd tbh.
if the pedal in front of the pedal has a low impedance output and the reverb/delay/wahtever goes in the loop, always has that series potentiometer, which even at the lowest setting has atleast some series resistance, wil average out to be just what comes in.

what you want is a passive mixer,


also, to avoid ground loops and thus hum, un-ground one of the send or return jacks, as the ground for the pedals already is provided by the other jack.

cheers

[pavle]

Thank you, I didn't understand your diagram consciously, but it seems to have sunk in somewhere.

I've got it working by connecting the middle lug of the SPDT to the OUTPUT, then a side lug to the pot, and then the pot back to SEND. Seems glaringly obvious now that the original article was off in it's instructions. 

[ashcat_lt]

In the ones I've built, I just opened up the pot itself and cut the track at the 0 end so that turning the knob down all the way does the same thing as your switch.  I do still have a true bypass stomp switch, but the feedback keeps feeding back (actually gets stronger) when it's bypassed, and that loud signal can couple to the other pugs of the switch and bleed through a bit.