Autoformer Can't Shut-off Source!

[zekk]

I've this autoformer for more than two years without fully understanding how to use it.

Problem is, I can never turn down the volumn.
Music still prevails at the lowest setting!

Source is a Gamut CD1 with 4v output > autoformer > SEUL TT22 with EL802 driver.

It was all wired up in an alu. casing originally.
I've it transplanted into an acrylic enclosure.

Also. what's that 3 positions switch for?

Kindly advice how I can fully ultilise this great innovation.

Thanks!