Vox ADVT30 - External Speaker mod

[Elliot]

I was thinking of making an external speaker mod - drilling in a speaker jack - I have the tech for that bit - i.e. you just buy a external chassis jack and solder it to the lug plate.

BUT how can you make it so the jack is switching - i.e. it disengages the internal speaker connected to the speaker lug plate when an external is plugged?

[PhilKing]

You need a switching speaker jack socket.  You connect it so that the contacts are on when the jack is not inserted (unlike a guitar where you want the connection with the jack inserted).  You can get them from Maplin I think (Re-An make them in the UK).  They are plastic and have 4 tabs.