Variable hi-pass/bandpass filter Continued...

[bufftonz]

hello alanlan,
(or to others who'd like to discuss as well)

this is a continuation of the "variable hi-pass/band-pass filter" discussion thread we had a few days back, but I'm not sure if you lost track of the original forum, but here is the new continuation just in case you lost track of the original forum thread.

here is the original portion of the circuit I am focusing on of my delay pedal: (as is seen in my actual pedal)

                                                         -   +
(input from IC chip)--------/\/\/\----------|(------------------------> (to middle lug of Repeat pot)
                                        22k               0.56uF

Below is the proposed experiment or proto-type mod you gave: (revised for electrolytic caps)

                                                             - C1+
(input from IC chip)---------/\/\/\-------------|(----------------------------> (to middle lug of Repeat control pot)
                                         20k       |         .1uF                     |
                                                      |                                    |
                                                      |                      ? C2 ?    |
                                                       -----/\/\/\---------|(------
                                                          47K VAR       0.47uF


(sorry but I meant to show an electrolytic 0.56uF cap to be converted to a different value in the original thread, but I forgot to mention this in the first part of the topic, my mistake).

1. Should C2 be also an electrolytic cap if C1 is an electrolytic cap (positv side in-rout to middle lug of Repeat pot)?

2. Also, I didn't quite understood what you meant by the shelving effect... like do you mean that if the variable 47k resistor was turn to max, most of the Repeat signal would pass thru C1 as more trebly? Likewise would turning variable 47k resistor down to minimum increase flow to thru C2 (bypassing more of C1) and come out as more bassy? Is this how you mean? Or am I still confused?

3. If that's so, then if I wanted the range of the bass frequencies of a .56uF cap, and the treble frequencies of the .10uF cap, would I just then  use .10uF as treble threshold cap (C1) and  use a .56uF as the bass threshold cap (C2)? Giving me a broader frequency spectrum sweep between .56uF to .10uF versus .47uF to .10uF? How exactly does this work, or how do you mean?

I'm definitely learning a lot here, which is good because I never knew this much about pedal electronics before. I look forward to your next reply. Thanks.

--Chris

[alanlan]

1. Should C2 be also an electrolytic cap if C1 is an electrolytic cap (positv side in-rout to middle lug of Repeat pot)?

No, not at all.  Just make sure that any electrolytic caps are put in the circuit with the + end more positve (in DC terms) than the - end.  In some cases, both ends are at the same potential so you just have to choose.

2. Also, I didn't quite understood what you meant by the shelving effect... like do you mean that if the variable 47k resistor was turn to max, most of the Repeat signal would pass thru C1 as more trebly? Likewise would turning variable 47k resistor down to minimum increase flow to thru C2 (bypassing more of C1) and come out as more bassy? Is this how you mean? Or am I still confused?

All I meant was that with the pot set to minimum, you will get a more bassy response, with the pot at max you'll get a less bassy response.  In between there will be a slight "kink" in the response.  It probably won't be audible as such.  What you should hear is something inbetween the two extreme settings.

3. If that's so, then if I wanted the range of the bass frequencies of a .56uF cap, and the treble frequencies of the .10uF cap, would I just then  use .10uF as treble threshold cap (C1) and  use a .56uF as the bass threshold cap (C2)? Giving me a broader frequency spectrum sweep between .56uF to .10uF versus .47uF to .10uF? How exactly does this work, or how do you mean?

That's right, C1 will set the limit of the less bass response sound, and C2 will set the limit of the more bass response sound.

I'm definitely learning a lot here, which is good because I never knew this much about pedal electronics before. I look forward to your next reply. Thanks.

Good!