Here's something I've been working on lately.
The Echomatic is an old Stompboxology circuit which utilizes a quad opamp as two splitters and two mixers, allowing you to take advantage of a three-head tape deck for delay effects. In simpler terms, you can plug this into a three-head cassette player (or reel to reel) to make a tape echo.
It sounds pretty cool. It's not going to replace anybody's El Capistan, but it's useful for some warm slapback or lofi, modulated ambience. Because the tape heads are fixed, the only way to adjust the delay time is by changing the motor speed. At low speeds (for longer delays) the motor is a lot less stable so it adds quite a bit of chorusy warble, and of course you lose a lot of recording fidelity by running the motor that slowly.
Anyways, here's my little demo. Pardon the um's and ah's and the awful compression from my phone. I'll record some better demos later.
https://youtu.be/2T2QTwdB-PQ
Here is the original article if you'd like to learn more, or build one yourself: http://imgur.com/a/NHRjW
All credit goes to Nicholas Boscorelli, who wrote the article