Simple ground question

[Hemmel]

Alternately, you could use two-two ganged pots and have two knob fading (edit: as shown in your schematic).

Actually... my schematic showed only one dual-ganged pot. This is what I meant :



Wouldn't this be sufficient ??

[ashcat_lt]

^^^That'll work well enough.  It works about the same as what jdsanti posted, except yours will have a little more bleed (because half the R between the two sources) and allows you to do stereo with only one dual gang pot.

[Jdansti]

^Right. I don't know if 10K is enough to avoid bleed through from the source that's supposed to be "off".

See the drawing below. When the pot is turned "toward" the TV, the computer sees 10K between itself and the console and vice versa.



Would it hurt to make the pots larger?

[ashcat_lt]

The optimal size of the pot depends on the impedances involved around it and the acceptable level of bleed.  The taper be decided by the relative impedance on either side.

...

On pot value - do you know what a voltage divider is?  Looking out from one of the sources, it sees a voltage divider where the top resistor equals its own out-Z plus whatever portion of the fader pot is between it and the wiper, and a bottom resistor equal to the rest of the pot plus the out-Z of the other source both in parallel with the in-Z at the mixer.  How big that ratio can get determines how much attenuation you'll get at the extremes - how much bleed will come through.  Honestly, 10K is probably plenty.

[Jdansti]

Got it. Thx. 

[PRR]

> stereo out and one knob fading, you'll need a four ganged pot

No, it can be done with one pot (per channel), though it will be lossy. Down 12dB is practical. You can probably find 12dB un-used gain in sources or console. http://i.imgur.com/zIyU6La.gif

I understand that spending MONEY is un-acceptable. Else I'd suggest that a basic Disco mixer has the whole deal covered. TV to input A. Flaptop to input B. Smash the crossfade slider left or right as needed. Non-junk disco mixers use sturdy sliders or VCAs so that wear is not bad. A poll of the regulars might turn-up an abandoned disco mixer.

I do think supporting the loss of one job and the overloading of another job is poor form.