Over the last few years I’ve made quite a few different modules, some never get to leave the drawer due to space, and others get slowly changed as my needs suit.
The delay came a Velleman kit from Conrad, which is always fun, but since then I’ve built a few others using the classic PT2399 IC.
The six into 1 is I cobbled together from various schematics from the book ‘Handmade Electronic Music’ by Nicolas Collins.
This book is great for just getting out and making things, with lots of simple but effective ideas that you can easily build upon. Highly recommended.