Here is a simply line level pre-amp that auto selects inputs.

AntiCrap

These circuit uses Thyristors as memory devices (drawn as transistors) and auto selects active inputs with a SECA headphone section and power supply.

Docfoster

Love the way you churn out these wonderful creations Colin. @-)
What is the pre-amp remembering in its Thyristors...?

AntiCrap

Which input was active last.

Docfoster

AntiCrap said:

Which input was active last.

Gotcha.

uglymusic

I've got one that does that. It's pretty cool.

AntiCrap

Yes it is Listen by TQ  :-w

uglymusic

Does this one improve on the Listen?

AntiCrap

Yes a little

uglymusic

And what would it cost to build?