http://www.runoffgroove.com/splitter-blend.html
I'm thinking about using part of this circuit for an idea I have. I want to use the blend section but I have a question.
I'm looking at the "green return" specifically here. I see how it's using the switch for phase correction but just before that there's a JFET buffer/boost/gain recovery thing going on. What's that for? Doesn't seem like it has anything to do with the phase correction. (maybe I'm wrong there)
And the "red return" section doesn't have the JFET stage, it's just capacitor coupled to the output buffer/op amp....
Somebody school me please!
the jfet is in an inverting configuration so it will flip the signal. edit: nope, it's a buffer.
the switch S1 basically determines if the op amp is in inverting or non-inverting configuration. notice that when S1 is closed, it connects the + input of the opamp to vref (signal ground), turning this into a basically a buffer, very similar to amp B. when disengaged, it turns into a modification of a basic inverting opamp.
the switch isn't really a phase correction, i think, but used as an effect. it could probably make many modulation effects more pronounced.
http://geofex.com/Article_Folders/polarity_reverser/polarity_reverser.htm
Here's the article that the link takes you to from the runoffgroove project document. No JFET section here.
I've seen similar phase inversion designs before. I'm going to look a little closer at both again to see if there's something I'm missing. Still looks like the JFET section is unnecessary to me.......
upon closer inspection, the jfet is actually a buffer and it does not flip the signal
i see your point about whether it is necessary or not. i'm not sure why the designer included it and i think the circuit could be simplified without it. possibly it's used to provide a low-impedance output to feed the opamp stage, not sure.
I wondered about it being a buffer too but then why wouldn't the "red return" have the same thing going on.
Not enough hours in the day but, as soon as I have some time I'll try breadboarding it both ways to see if there's any advantage to using it.......
Got an email from Brian Tremblay at Runoffgroove with a link explaining it much better. The JFET is a buffer used to keep the green channel at the same 1 Meg input impedance as the red channel when using the phase inversion. Depending on what effect is feeding the input, it may not be necessary.
There's also an improved design in the post that just uses one op amp for the input buffer in the splitter. You can then use the other half for the buffer before the phase inversion if needed.
Pretty good stuff if anyone's interested....
http://www.diystompboxes.com/smfforum/index.php?topic=112143.msg1038674#msg1038674