How do I make a variable hi-pass/bandpass filter?

[bufftonz]

How do I make a single-knob Tone control circuit on my analog delay pedal (to control tone of repeats)?

Currently this is the portion of the circuit I'm working on below:

(input from IC chip)------------------/\/\/\-------------||-----------> (to middle lug of Repeat Control pot)
                                                    22k                   .56uF

Mark mentioned to me that the below configuration would give me brighter and longer echo repeats with a bass roll-off around 170kHz:

(input from IC chip)-------------------/\/\/\-------------||----------> (to middle lug of Repeat control pot)
                                                    20k                  .47uF
But how do I make this part of the circuit adjustable (via control knob/pot) in terms of bass/treble balance? such that I can control the contrast between bass or treble frequencies of repeats? Do I need only to make a variable low-cut filter(hi-pass) or should a I make a variable band-pass filter to manually control contrast between bass freq and trebloe freq of echo repeats?

I look foward to all of you help, or any suggestions, advise, and tips.

Thank you.

-- Chris

[alanlan]

One idea worth experimenting with:

(input from IC chip)

-------------------/\/\/\-------------||---------------------> (to middle lug of Repeat control pot)
                       20k        |         .1uF                   |
                                    |                                  |
                                    |                                  |
                                     -----/\/\/\------------||---
                                         47K VAR          0.47uF

You'd have to experiment with the values, but basically with the variable resistor at minimum, you get extra capacitance so more LF response,  and as you wind up the variable resistor the effective capacitance diminishes and you get less LF.  It will provide a shelf response.

If you could post more of the circuit in question, I could be more specific.

[bufftonz]

The question is though, with the configuration of the mod with variable resistor, where would the middle lug of that variable resistor (pot) go to?  The part of the circuit I was told that needed emphasis was the portion that I showed earlier (the input from IC chip going to resistor, then thru cap, then to middle lug of repeat pot. (just look for the part where it says "Repeat" and the surrounding areas of that portion. Here is a link to those schematics:

http://www.freeinfosociety.com/electronics/schemview.php?id=2322

Unfortunately I only have a 50K variable resistor(pot) with me on hand to work with. Is this OK to use in place of the 47K pot you suggested? I couldn't find any 47K pots at the local IC Supply Store; the closest value was 50K.


Please let me know what you think of the schematics, and what you thought so far for the Repeat section of the circuit (the part where there is a variable resistor that says Repeat, and the series 0.56uF cap and 22k resistor that come before it (as the middle lug of the Repeat pot).  Once again, many thanks.

--Chris

[bufftonz]

Oh I also forgot to mention, which by the way is most important; the capacitors are electrolytic, with the positive side going in-route to the middle lug of the Repeat pot. Sorry for the delay and slight confusion. Perhaps this will better help your assessment of the circuit in focus. Thanks.

--Chris