GrandPoobah

I ordered a tire and some other odds 'n ends from the website on Thursday night; both packages arrived the following Monday (UPS Ground). The tire price matched what other internet vendors were charging. I was happy.

Just came across this thread, but in case anyone's still interested: Tesseract makes a product that does the mixing and amplifying that you're looking for, and it's significantly cheaper than the Autocom. Changing the wattage of the resistors won't help. The attenuation that you've noticed is a characteristic of this type of circuit, and it increases for each input circuit that you include. The only solution that I know of is to add an amp after the mixer. I've been thinking of doing exactly that myself, using this design and building it all on one board. I'll post back if I ever get around to trying this. One consideration for anyone thinking of doing this is that some electronics designed to run off of external 12 volt power use an amplifier configuration known as Bridge Tied Load (BTL). In these devices the negative speaker or headphone output terminal isn't at ground, instead it's given a signal that's the inverse of the positive terminal. With these devices the negative terminal shouldn't be tied to ground as in this mixer circuit. There's two ways that I know of to deal with this: one is to use a transformer to isolate the input source from the mixer, and the other is described in Figure 6 of this datasheet. The Valentine 1 does not use a BTL amp to drive it's headphone jack, but the Escort 8500 does, and your scanner might too.