The spring king is a real spring reverb from the 90's, they decided it wasn't bouncy enough so they added a slap back delay, you could turn the reverb off and just have slap back, but you couldn't turn the slap back off, the first mod I placed on this pedal was to be able to turn off the delay, and as it turns out, the spring reverb sounds fantastic on it's own, the slap back made it sound corny/fake, played on top of a guitar amp it will reverberate even better, but even used direct for recording it's quite nice, I also added controls for the delay, which can get crazy with self oscillation, I have used this for recording, bouncing tracks through the spring reverb, I particularly like the tone control, love this effect but I am not recording and want to make space for some other equipment
Added switch that turns the delay completely off, this has two functions, when the unit is first plugged in/turned on the delay will not sound and you'll only get spring reverb, you can then flip the switch and the delay will be on, but depending on the settings when you turn the switch back off, you'll get some wonderful synth tones
The left knob controls the amount of feedback, this can go well into self oscillating madness
The right knob controls the delay time, this goes from extremely short doubling, to crunchy distorted long delay
Here is a video of a spring king with the same mod, https://www.youtube.com/watch?v=OAg4EHVpM5w