adhu enna instrument?

[ananth222]

In the beginnig of the second stanza of "nee dhAnE endhan ponvasantham" what's the instrument played alogside acoustic guitar producing "wocawoca...wocawoca" kinda sound

A better example...beginning of "senyorita I love you" from johnny has the same instrument...Isn't this electric guitar ?

Heard it in some old pop albums and to some extent in jimi hendrix as well

That is a processed electric guitar. processing alters the sound of the guitar, and there are many popular processing techniques. IR uses "Wah", "Phaser" and "Flanger" a lot in his songs. The three are a bit similar to each other, and alter the tone and give a waxing/waning sort of sound to the guitar. This song u mentioned seems to use wah effect. Ilaya nila also uses phaser throughout the song. The ending gutiar in "chamber welcomes thiagaraaja" is also using flanger/phaser.