Need a Passive Mixer Circuit that allows for disconnected sources

[azira]

Ordinarily a passive mixer circuit is pretty straight forward, just a series of mixing resistors from the sources (such as: http://www.tkk.fi/Misc/Electronics/c...linemixer.html )

This works when both sources are connected. But the problem is that the attenuation of a source changes depending on the number of sources connected. For example, in a 2-ch mixer, each input is attenuated by half, if you unplug one source then the attenuation ceases and suddenly you get an output that is 2x as loud.

Does someone have a reference to a passive mixer circuit that has a consistent attenuation whether or not the inputs are connected?

Thanks.
--
Danny

[Pjotr]

With a passive mixer unconnected inputs should go to ground. Preferably by a small resistor of app 220 ohms. There are TRS input sockets with a build switch suitable for that.