Marshall 2550 schematic

[Leevi]

I don't find an idea for the drawn line from VR1 to ground.Is it just an error or is it trying to describe something like mute?

https://el34world.com/charts/Schematics/files/Marshall/Marshall_25aniv_silverjubilee_25_50w_2550.pdf
/Leevi

[sluckey]

I don't find an idea for the drawn line from VR1 to ground. Is it just an error or is it trying to describe something like mute?

That line is actually connected to the switch lug on the input jack. It's not connected directly to ground, even though the schematic seems to show that. The purpose is to mute the preamp whenever nothing is plugged into the input jack.