Modifying the Gravitation Reverb for Self-Oscillation

[MickeyP]

Hi there, first time poster here,

I'm planning to build the Gravitation Reverb, and I'm interested in adding a self-oscillation feature activated by a momentary footswitch. While I have experience with tube amp and clipping circuits, I'm less familiar with time-based circuits.

My question is: How can I modify the Gravitation Reverb circuit to incorporate a self-oscillation footswitch?

Any advice or suggestions would be greatly appreciated. Thanks in advance!

 

[jwin615]

IC2 pin 1(or common node) ->. 200n film cap -> potentiometer or trimpot as a variable resistor(experiment with value but I think lower, like 1-5k is where I would start) -> momentary footswitch. -> IC2 pin 6(or common node)

You could also just try pin 5/6 of the brick to pin 3 of the brick but I think utilizing the buffers would be ideal.

You'll want the pot/trim pot to be able to set the amount of signal fed back.
If it shrieks into ugly high pitched digital feedback too much or too quickly, try sticking a RC LPF in the loop somewhere. A 120 ohm resistor followed by a 120nf film cap to ground would roll off at around 11khz.

 

[Riccardo Turacchio]

Really interesting
Please post a build report and video once it's done
I love this kind of stuff

 

[Riccardo Turacchio]

Im waiting for a Spirit box, also with brick....I wonder if a mod like that could work also on this circuit...

 

[MickeyP]

IC2 pin 1(or common node) ->. 200n film cap -> potentiometer or trimpot as a variable resistor(experiment with value but I think lower, like 1-5k is where I would start) -> momentary footswitch. -> IC2 pin 6(or common node)

You could also just try pin 5/6 of the brick to pin 3 of the brick but I think utilizing the buffers would be ideal.

You'll want the pot/trim pot to be able to set the amount of signal fed back.
If it shrieks into ugly high pitched digital feedback too much or too quickly, try sticking a RC LPF in the loop somewhere. A 120 ohm resistor followed by a 120nf film cap to ground would roll off at around 11khz.

Thanks!

Looking at the circuit, I see this would kind of do the same thing as the Atmosphere pot,... I think. Would it be an idea to circumvent the Atmosphere pot all together, by connecting C6 to C5 with the momentary footswitch, for self-oscillation?