This is two versions for Slew limiter/glide/slide/portamento/call it whatever you like. They are very easy to build.
They work with 9v single power supply but 12v is good too, so you can integrated them in some of your mini-synth hardware projects.
Why 9v? Because I have a project of 9v mini-modular in progress.
(so sorry for my dirty schematics, I must to learning to work with a CAO software…)
PS: I have used lm324 to build two of them, but you can use any kind of dual opamp (lm358 for exemple)
Test it, slide it, and having fun to surf on the signal !!