Trying to get panner from Geofex working

[sfprint]

Sorry if this is painfully obvious but I can't find info on it. Where does the "Vb" on these circuits connect to? (page 2, 1st schematic, this is the one I'm trying to build)

http://www.geofex.com/Article_Folders/panner.pdf

To test this out, I have my ipod's L and R (different info coming out of each) connected to A and B or Input and Effect Output. In both this diagram, and also the one in the box on the first page, I've tried the same thing and only one side comes out, and when panned to the other side, nothing. I'm sure it's something I'm doing wrong....

Any help would be wonderful.

Thanks!

[R.G.]

Vb is a bias voltage, halfway between +9V and ground. You make it by connecting two equal-value resistors in series between 9V and ground, the connecting a biggish capacitor between the middle of the resistors and ground. Common values are 10K for the resistors and 10uF to 100uF for the cap.

It's likely that you do have  a circuit problem. I've built that panner many times and it definitely works.

[R O Tiree]

If you scroll down to the very last drawing on that pdf file you'll see, at the bottom, slightly left of centre, 2 10k resistors connected between +9V and Ground with a 22µF capacitor and a little arrowhead with "Vb" written next to it coming from the junction of those 2 resistors. You just have to make sure that all the points marked "Vb" on the diagram you're using are physically connected together. (It means "V bias", as RG said).

You'll find that it's a fairly common convention... All the points with little inverted triangles are (usually) Ground and should also be connected to each other (and the -ve terminal of the battery!) and all the points marked "+9" (or similar) likewise. Sure, RG could have put all those wires into his drawing, but I think you'll agree it would end up looking like a rat's nest. Labelling all these reference voltages as we do, it's quite easy, after a little practice, to imagine all these extra connections and it makes following the signal flow in these diagrams a lot simpler.

Last point - 2 10k resistors works for this circuit. The same values might not work on others, giving a Vb too low or too high. There's a useful thread on here somewhere about choosing the right values. That little circuit fragment (2 x 10k resistors, 1 x 22µF electrolytic cap) will work quite comfortably for all the circuits in that pdf, though.

[sfprint]

Thank you very much, both of you. I finally got it working. I've been looking for a circuit like this for awhile and I'm very happy with it. Thanks again.