high pass filter question

[fuzzy645]

So on a guitar circuit a really common mod to the volume pot is to put a high pass filter, usually as a 680 pf cap in parallel with a 220K resistor implemented as in the picture below. The idea being as our roll down the pot, you will retain highs (and not sound muddy).


I'm trying to compare this to the more general electronics info about high pass filters such as that found here:



These seem different to me.  In the 2nd one, the cap and resistor are in series and the the resistor follows the cap (so the order is cap to resistor to ground).

In the image I provided though, it does not seem that way (even though this is a common way to hook it up). It seems like the cap and resistor are in parallel, and the 2 of them are then in parallel with the pot (I think). 

Questions:

1. Is this correctly called a high pass filter (the first image), even though it doesn't seem to be in the same order (to my eyes)?

2. would raising the cap value (above the 680 pf) then retain more highs upon rolling down the volume, or would that be the opposite?

3. I've seen it both WITH and WITHOUT that 220K resistor, as well as with values ranging from 150K to 220K+?  What is the point of this resistor?

[wavley]

I believe your confusion comes from the first circuit being a treble bleed circuit, it's works differently, if someone hasn't explained by the time I get home I'll try to expand on that for you, though I'm not as good as someone like RG at explaining these things.

[Gurner]

Your equivalent circuit is not showing the bigger picture, so I just knocked up this on to help you visualize...



....obviously those two resistor represent the pot... either of them vary in resistance (ie as far as the wiper position is concerned). The idea being, the high frequencies have a sneeky backdoor path direct to the wiper through the cap

[ashcat_lt]

Neither of the resistors in the "treble bleed" picture are the same as R1 in the general high-pass pic.  That R1 would be the input of whatever the guitar is plugged into.  Without the pot or the parallel resistor it then looks exactly like that textbook filter.  Both the resistor and the "top half" of the pot bypass that cap.  It's best to think of it almost like a clean blend.  The pot blends in some "clean" (unfiltered) signal, and the resistor tapers that response.  Or something.

For more than you ever wanted to know about treble bleeds.