Active or more accurate low/highpasses

[ExpAnonColin]

Other than the ultrasimple one cap one pot ones, what is there?  I want it so that it's a bit more... filtery, instead of just like the tone knob on your guitar.  More like an actual low or highcut filter rather than a lowcut mix knob or a highcut mix knob.  Any ideas?  Doesnt have to be passive but it'd be nice to be non-complex.

-Colin

[bwanasonic]

You may want to check Craig Andertons "Super Tone Control" from Electronic Projects For Musicians. It incorporates high/band/low filtering with a Q control.

Kerry M

[Rob Strand]

The next simplest low-pass is like the one used on the Proco rat.  You can convert that idea to a high-pass by swapping the R and C positions - you will need to increase the cap and/or increase the R since, for typical audio apps,  the high-pass cut-off is usually a factor of 100 lower than a low-pass.

To get more filtering than thisyou need a second order filter.  The most common form of this is the Sallen and Key filter circuit.  You can make these variable as well but generally you need a dual pot - in general blending outputs on these isn't recommended since you often end-up with unintentional notches.  There's a lot of web info on Sallen and Key circuits, most involves a lot of math - if you hunt around you should be able to find something which you can understand.

[ExpAnonColin]

The next simplest low-pass is like the one used on the Proco rat.  You can convert that idea to a high-pass by swapping the R and C positions - you will need to increase the cap and/or increase the R since, for typical audio apps,  the high-pass cut-off is usually a factor of 100 lower than a low-pass.

To get more filtering than thisyou need a second order filter.  The most common form of this is the Sallen and Key filter circuit.  You can make these variable as well but generally you need a dual pot - in general blending outputs on these isn't recommended since you often end-up with unintentional notches.  There's a lot of web info on Sallen and Key circuits, most involves a lot of math - if you hunt around you should be able to find something which you can understand.

Yeah, I was thinking more along the lines of a 2nd order inverting op amp design... it's the math that I don't want to do, but I'll probably end up doing it just so it's my "own" design.

-Colin

[Paul Perry (Frostwave)]

This might be crazy.. but, if you had a noise source & a real-time specrum analyser prog on your PC using the soundcard, then you could tweak the R &C values & watch what was happening!  maybe come up with something 'non-standard' but musical. Some wah circuits must have been 'empirically' determined..

[ExpAnonColin]

This might be crazy.. but, if you had a noise source & a real-time specrum analyser prog on your PC using the soundcard, then you could tweak the R &C values & watch what was happening!  maybe come up with something 'non-standard' but musical. Some wah circuits must have been 'empirically' determined..

'

Couldnt I do the same with a nice white noise funct. generator and an oscilloscope?

-Colin

[Paul Perry (Frostwave)]

Couldnt I do the same with a nice white noise funct. generator and an oscilloscope?

-Colin

Well, you might be able to do it wiht a swept oscillator, but filter outputs slew around weirdly sometimes when the frequency of te input is changing. I was hoping there would be some way you could actually see the response in realtime, rather than measure points, which would get old pretty quick.