Sorry I'm late back to the party with this, we are minding grandchild No.8 today and I've been on poppy duty

I can't remember who referred me to these, I was looking for an old Electronics Today magizine circuit for a guitar box called an attack delay unit. No one could help with that but included in these links is the Boss Slow Gear ( Boss SG-1 ) which is/was the same thing it fades onto the note so you can get a nice violin effect and the one I built back around 1970 gave a beautiful creamy overdrive on bypass so I probably stuffed something in the build.

Here's a bunch of schematics and kits
http://www.generalguitargadgets.com/...lp/schematics/

And another site with just kits and stuff
https://www.pedalempire.com.au/collections/byoc-pedals