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I built a variation of this circuit from Beavis Audio Research and it works great for some modulation pedals. As it is not complex, I would like to fit it in some future builds as a mod as opposed to building it as a standalone pedal.
I know this is a dumb question, but does anybody have any recommendations on how I should go about connecting the inputs and outputs of a PCB/ 3PDT wiring configuration with the circuit below? My worry is connecting the tip of the input jack to the input of the board as shown below would negate the ability to bypass the effect.
Here is a picture from Beavis Audio for a 3pdt version. I could never find it on his site and I am not sure where I grabbed the screen shot from…sorry the resolution isn’t great. I am by far not an expert on this but if you treat the BI and BO on the 3pdt board as the send and return jacks and hook through a switch as shown then the feedback should not “bleed through” when the switch is off.
Further to this…I have built several pedals that would fall into the “noise” category that have options like “chaos” or “feedback”, etc. and generally they are just connecting the output back into the input somewhere with some resistance in between and activated by a momentary switch (normally open).
I have built a couple feedback loopers using the Beavis diagram and have found that it is extremely dependent on what pedals are in the loop. I also find that the pot effect on the feedback is very dependent on the pedals and pedal settings.
I have recently been working on a feedback looper with some more options on it. It is still in the “prototype” phase so please ignore the rats nest wiring at the moment. It will be cleaned up once I finish up some of the changes below.
- “Feedback” switching goes through a DPDT latching then an SPDT momentary. The DPDT is an “on off” for the feedback loop (used DPDT to include LED) and the SPDT acts as a “momentary opposite” of how the DPDT is set. So, if the feedback is off then the SPDT is used to turn the feedback momentary on. If the feedback is on from the DPDT then the SPDT acts as a momentary way to turn the feeback off.
- Inline with the feedback pot I have put a mod board that outputs a triangle wave through a vactrol to produce a variable resistance.
I need to make some changes to the modulation effect wiring and experiment with some different vactrols. I have a couple other “mod boards” on vero that I would like to try with square wave output as well as both triangle and square wave switching. For now the biggest issue is bleed through clicking from the mod board LFO. I am going to re-wire and use a 3PDT toggle for the modulation that actually cuts power to the mod board when not being used and will wire directly from the power jack instead of through the 3PDT wiring board and add ground wires from the board to the jacks instead of just using the enclosure as ground. An added benefit of this will be the rate LED for the modulation will not flashing unless the modulation is on.
Anyway, just thought you might be interested. What pedals have you had the most interesting results with? Aside from modulation I get some craziness whenever there is a Big Muff circuit in the loop.
Very interesting. Keep us posted.
Hello Brooks and Wilkie. Thank you for your posts and for your feedback (no pun intended) Brooks. The graphic you posted from Beavis Audio was the pedal I built. As for success with the pedals I have had, it depends on the pedal!
What made me want to incorporate a feedback circuit into a pedal itself was that I tested a PCB Pedal I made named after a certain pedal named after a woodwind instrument. It’s basically a fuzz/ one step delay pedal with modulation of over/ under an octave. Because the delay never went past one repeat on the pedal itself, it worked beautifully with the feedback pedal to oscillate and never get out of control. I have had success with a couple fuzz pedals but never spent enough time experimenting with them.
Perhaps it was the gin rickey I had at the time or perhaps I was overthinking the fact that all I needed to do was throw a couple jumpers between the input and output of the PCB separated by a pot. I did that, used a 1 Meg logarithmic taper pot, and decided to forgo a switch. Suffice to say it works beautifully. The pedal is a tandem with a Boss Slow Gear type pedal running into it.
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