Building a simple high/low eq box

[Joecool85]

As the title says I'm interested in building a simple high/low box, just to cut volumes, not to gain. 

Here is what I was thinking

For the High Pot
In     Out     0.1uF to ground

For the Low Pot
In     Out     Ground
  1.0 uF

So the high would only be cutting frequencies that go through the 0.1uF (that should be kinda high freq right?) and the low would cut everything except what bypasses it via the 1.0uF cap.  Now, this is all theoretical at this point, but what do you guys think?  Is this the right way to do it?

[Mark Hammer]

Since capacitors provide a lower-impedance path, the higher the frequency, in principle you are correct.  So, a tip of the hat for taking what you've learned, and putting it to good use.

The sticking point is component values.  The frequency where the rolloff "begins" (or rather, begins to be noticeable) will depend on the joint effect of the cap and whatever relevant resistances are involved, not just the cap.

The simplest possible case is a standard RC lowpass filter, where the resistor is in the signal path (i.e., between in and output), and the cap goes to ground.  Here, the point where the rolloff is said to begin is dictated by the formula F = 1/(2*pi*R*C), where R is in megs and C is in uf.  If R = 47K (.047M), and C = .01uf, then any rolloff of higher frequency content would be at 6db/octave, starting around 339hz.  Kinda low, eh?  Same cap, but a 10k resistor, and that changes to 1591hz.

I'm still not absolutely crystal clear on what you want the box to do (I *think* it is to go from a mellower to a thinner, brighter sound in a footstep), but an excellent place to start would be to look at the tone "switching" scheme from the Little Big Muff Pi, as well as the article on presence controls over at AMZ.  The Big Muff Pi tone circuit uses a combination of lowpass and highpass filters, similar to what we've both (you and I) described.  In the BMP, and similar circuits, the tone knob simply pans between these two filter circuits to give a blend of thin, reedy tone (highpass), and muffled "wooly" tone (lowpass).  Naturally the resistor and capacitor values are chosen to give a reasonable or desirable balance of high and low when the control is set to the middle.  In the Little BMP, there is no variable control, but rather a switch that selects from the one extreme setting or the other, which souds to me to be kind of like what you want.  Jack's excellent article over at his AMZ site provides some useful examples of how one might make such a control anmd have it customizable.  Worth a read.

[Joecool85]

Well, thats not exactly it.  Basically I want two knobs, one for high and one for low.  Almost like tone knobs on a guitar, just better.  I would put a switch in it so that I can go from regular to trebley, or regular to bassy depending on how I turned the knobs on the box.  Make more sense now or no?

[Paul Perry (Frostwave)]

If by "simple" you mean passive components only, I think you might be disappointed by the los of gain, and the effect not being severe enough. Maybe get some inspiration from speaker crossover designs? A design wiht inductors as well as caps is going to be better.

[MartyMart]

If by "simple" you mean passive components only, I think you might be disappointed by the los of gain, and the effect not being severe enough. Maybe get some inspiration from speaker crossover designs? A design wiht inductors as well as caps is going to be better.

Such as "Craig Andertons" passive tone control, using an inductor ?

Marty.

[Joecool85]

That sounds about right, have a link for that?

[MartyMart]

That sounds about right, have a link for that?

No, but it's in his book "electronic projects for musicians" which is well worth having
and has several great projects, albeit a bit "dated' 

Marty.