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Passive Crossover for guitar/bass?

1/30/2003 3:18 PM
Nic Neufeld
Passive Crossover for guitar/bass?
I need all of your expertise, gentlemen!  
This is what I'd love to do. Take a small aluminum enclosure and build a PASSIVE crossover into it. One 1/4" input, two 1/4" outputs. Install a potentiometer on the top and have that be the adjustment for the point at which the highs and lows get split. With two amps, that would be an ultimate tone shaping device, for bass OR guitar. It would have to work for the relatively weak passive signal from the guitar or bass, so we are dealing with guitar level, not speaker or line level. Anybody have an idea?  
Also, what I do now from time to time is send my signal straight into both amps, and then EQ them so one is bassy and one is bright. This isnt the same as how a crossover works, right? If the crossover won't make it sound better I won't bother...  
But anyway, your ideas, hints, suggestions, comments, snide remarks, etc. are welcome!  
Nic Neufeld  
email me at
1/30/2003 9:14 PM
Too much signal power required to do this passively.  
Coils are expensive too.  
Really much easier and cheaper to do this with an opamp based design.  
Why are you stuck on passive circuit?
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1/31/2003 5:45 PM
Nic Neufeld

I just thought it would be easier and simpler...I'm not stuck on any idea, really. Whats a good opamp design, then?  
1/31/2003 7:54 PM
Unless you can find some specific solution, I think you could approach this problem in a similar way to bi-amping or tri-amping a stereo system.  
Most of these crossovers are fixed. You want variable frequency crossover points.  
This should give you an idea of concept of the fixed point type:  
There are pros and cons to any filter type, but to have control over the crossover frequency, most folks use the Sallen-Key type. Don Lancaster is the Sallen-Key guru. His book has good design info for this kind of task:  
Good article from ESP:  
After you have picked up a few buzz words, you might find something more specific on the net from a Google search.  
Most design info I have found is limited to the actual filtering circuit. Most filter designs want to be driven by a low impedance source so be sure to buffer the input with a voltage follower.  
Finally, be sure to control the gain of your crossover(s). You may have a net signal gain out of the crossover so make provision for attenuation at the output. A voltage divider on the front end of a voltage follower is a good way to do this.  
Good luck.
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