# Gravitation Run-away



## chip (Jun 2, 2022)

I'm in that phase where I ordered the PCB and am going over the schematics and stuff, getting all excited about building it while it's shipping.

In videos of the Gravitation and similar pedals, I've seen it where the reverb will feed back on itself and go into full run-away. I can't tell if that's entirely because of the Atmosphere knob (which seems to literally send some of the output back into the input) or if other things need to be set a certain way to make it go there...by that point in the videos, it's basically everything all the way up. I was thinking that it would be cool to have a momentary switch that would send it there on command without having to turn knobs, and if that could be done just by bypassing the Atmosphere pot, it wouldn't be that hard to do. Does that sound like it would work or will I just blow it up?


----------



## Funnel (Jun 2, 2022)

In my experience the atmosphere knob is responsible for the oscillation. Luckily chuck posted a digital reverb based on the levitation and the springboard. He explains what does what well. You could connect a spst NO switch between lug 2 of the atmosphere and the lug 2 pad.  That would make the atmosphere knob only work when the foot switch is engaged. https://forum.pedalpcb.com/threads/this-week-on-the-breadboard-a-digital-reverb.11997/#post-124345


----------



## chip (Jun 2, 2022)

Cool, thanks, I'll check out that thread.

I was thinking that I could just put a spst NO switch between lugs 2 and 3 of the atmosphere pot so that the knob would usually work normally, then when the switch is pressed it would essentially bypass the pot and send everything into feedback loop, as if the pot were suddenly turned all the way up while you're stepping on it.

It might need a resistor to ground or something to keep it form making a huge pop (if it would work at all). Not sure.


----------



## Funnel (Jun 3, 2022)

I might be opening mine up this weekend to adjust the 100k resistor so that it is more useable for my taste. If i remember I'll see if jumping lug 2 and 3 will work.


----------



## chip (Jun 3, 2022)

Eh, don't fry anything on my account (but I appreciate the offer). I was talking to some other folks about this, and it might be more complicated than I was hoping.


----------



## HamishR (Jun 5, 2022)

"I'm in that phase where I ordered the PCB and am going over the schematics and stuff, getting all excited about building it while it's shipping."

I find it extremely difficult to build a pedal while it's shipping. Any secrets?


----------



## chip (Jun 5, 2022)

You put on a pair of Umbros and get a soldering iron _real hot..._


----------



## chip (Jun 11, 2022)

Just to follow up...it works.

It's not perfect. The other knobs and switches have to be set in a way that it _can_ run away, but if they are, it will. The Atmosphere can't be all the way down because when it is AND pins 2 and 3 shorted, it puts that pot in a weird state. I briefly messed around with adding a fixed resistor in there so that it it was like the knob could never really be turned all the way down, but ultimately found it not worth it (this pedal is just for me, and I'm willing to deal with oddball scenarios).

There also isn't really room for a second footswitch in a 125B because of the little peninsula on the PCB for the LED, so I just added a small 1/4" jack to connect an outboard momentary switch.

Edit: see later post


----------



## Robert (Jun 11, 2022)

The upcoming SideEffect module would be cool in this application.  

One footswitch... press to activate/bypass, hold to run away.


----------



## chip (Jun 11, 2022)

Robert said:


> The upcoming SideEffect module would be cool in this application.
> 
> One footswitch... press to activate/bypass, hold to run away.


Oh, cool. 

Did you design this circuit? Do you think what I've done seems ok?


----------



## chip (Jun 11, 2022)

Lol, I think maybe no. My Atmosphere knob no longer works.

Edit: I think I know why...I think the jack I'm using is grounding one side of it to the case. It worked when not in the case, but not once it was in the case.

This is probably a bad idea. It's also sending signal all over the place and probably making an antenna. I should wait for the SideEffect module or come up with a better way of handling the switching where it doesn't literally send signal outside of the case.


----------



## chip (Jun 17, 2022)

Ok, I got this figured out. I think my idea was conceptually correct...and my initial implementation of it was wildly flawed.

Shorting pins 2 and 3 will make it go into feedback at will, assuming that everything else is set in such a way that it _would_ go into feedback if the Atmosphere knob was all the way up (for example, I don't think it will ever go into feedback if the Length switch is set to "short"). It also won't go into feedback if the Atmosphere knob is all the way down, because at that point it's sending everything to ground on pin 1 regardless of whatever else is happening. So it's not "safe," like most commercial pedals where all knob settings result in something valid, but I think it adds a ton of flexibility to be able to leave the Atmosphere knob and 10:00 (or whatever) and have it not go crazy for most of a song, but then to be able to have it to go crazy (and stop going crazy) when you want, with your foot.

I had it in a 125B and there was no room for a second switch, and at first I tried to add a jack to connect an outboard momentary switch, but that was a bad idea for a bunch of reasons. The real solution was to just put it in a 1590BB. I still needed to make some "modifications" to the PCB (including amputating the entire peninsula where the LED is supposed to go), which may have impacted the long term prognosis for this build, but I think that was mostly poor planning and not a limitation of the concept.

It's now doing exactly what I wanted.

Full writeup with pics and stuff is here: https://dunningkrugerfx.com/vacuous/


----------

