Del Casher Dead: Wah-Wah Inventor, TV & Film Composer Was 88

Del Casher -- the inventor of the wah-wah pedal, renowned guitarist, and film and TV composer -- has died ... TMZ has learned.

The musician-turned-inventor passed away on Oct. 1.

Working alongside Vox and the Thomas Organ Company ... Del used a transistorized mid-range booster circuit designed for trumpets to create the wah-wah pedal in 1967.

Throughout his storied career ... he appeared on screen and played guitar across from Elvis Presley in "Roustabout" and Jerry Lewis in "The Patsy."

He also composed for more than a dozen TV shows and films ... and was part of the studio recording unit called the "Wrecking Crew" that backed music legends like Frank Sinatra, The Beach Boys, and The Monkees.

Since Del's death ... a GoFundMe has been set up to help Del's widow Eiko with finances.

Organizer Al Burg writes ... "Eiko is now facing overwhelming financial and personal challenges at a time when she should be surrounded by peace, care, and stability. ... Tour donations will help Eiko pay down huge credit card debt and move into assisted living, where she can have safe housing and the increasing care she needs."

He was 88.