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Notch filter with sweepable frequency and adjustable width?

T

tbassist4

Aug 21, 2005
614
24
Boulder, Colorado
#1
Hey everyone,
I've been experimenting with a piezo buzzer used as a contact mic on both electric and upright bass. It actually sounds pretty good, save a bit of mid-range honkiness that my amp's EQ can't quite tame due to fixed frequency EQ. The rest seems good except for this one small band.

Is there a schematic out there for a notch filter where you can sweep the frequency and the width of the filter (Q value)? I'm still learning electronics so I'm not quite up to designing it myself.

Ideally it would be in pedal/box form and be something like this:
On/Off Switch w/ bypass (duh..:D)
Frequency Sweep Knob
Frequency Cut Knob (amount of cut)
Bandwidth Adjust Knob (Q value?)

And that's it...seems like it should be simple but I just don't know where to start in terms of making the frequency and Q adjustable - how to determine their range and effect and all that....

Any help would be greatly appreciated!
 
#2
There are several ready-to-go pedal and rack mount format para EQ's that may work for your given application...Nathan East (discontinued but still pop up now & then), Empress, and the Presonus EQ3B which I use. The EQ3B would need to be placed in your FX loop, though, but it does provide 3 bands which are fully adjustable (freq, width, and level). I've found them used for $65-80.

Riis
 
#4
SGD Lutherie said:
Are you using a buffer for the piezo? If not, that's where the honk is probably coming from.

The book "Electronic Projects for Musicians" by Craig Anderton has a project called the Super Filter, which has a sweepable notch function with variable Q.
Click to expand...

Yes, I'm using this one here: The Mint-Box Piezo Buffer.

The sound is much better than without it, but I'm wondering if I got something wrong as that was my first electronics build. I'll have to check it against the schematic later and make sure everything's in place.

I'll have to check out the book - but perhaps I'm asking for something too obscure? Perhaps a simple one band parametric EQ would do the trick just as well, plus the option of boost if I ever needed it?
 
#6
SGD Lutherie said:
Have you tried moving the piezo buzzer around? You may need to find a different spot to mount it.

Manufacturers spend a lot of time designing these things because it's easy to make one that sounds bad. You might not get any better tone from that buzzer.
Click to expand...

Just a little - since this can't go under the bridge foot of an upright, and tape is no good on the body of an electric, should I use something like poster putty to attach it to the bridge or body? I'm trying to thing of solid ways to mount it and that's the best I can come up with so far - I'll try it when I get home tonight.
 

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