Variable LP/HP Filter

Thread Starter


Joined Dec 21, 2011
Hey, I'm hoping you guys can help me, because I can't find any other place on the internet to find what I need, or at least that I know that it's what I need.

Here's my idea:

I'm a DJ and I have a solid mixer, RCA line in, RCA line out. The mixer of course has lots of other parts, but hopefully I don't have to work into too much.
What it DOESN'T have is a filter, which I want. Now I could pay $400 for a new mixer, but being a techy guy, I would love to do it myself.

What I'm looking for is how I would add a variable low pass filter onto the circuitry. If that's easy enough, I would also like to add a main selector for LP/HP. And if that goes well, I would also love a resonance adjuster. (Although I have no idea how that's done). Oh and of course an On/OFF toggle.

|...Q...| -Rotary Switch between 2 positions, LP/HP
|...O...| -Resonance Potentiometer
|...O...| -Filter Cutoff Potentiometer
|...X...| -IO toggle button

Then hopefully I can add a toggle to each channel for the filter to affect it.

Considering all the current in the mixer is at line level, I wouldn't have to do anything with amps, right? How would I go about doing this? Much appreciation for any help at all :D


Joined Feb 19, 2009
So you are looking for a 1 channel parametric EQ?

Adjustable center frequency
Adjustable Q (Width of filter effect)
Adjustable gain (more or less cutoff)
Hi Pass / Low Pass switch
Switch to take the PEQ out of circuit.

What is the input voltage? Standard 1,2, or 5V peak-peak?
Input impedance of your mixer?

How much experience do you have with electronics, reading schematics, terminology, etc.

What do you have for tools? DMM? Osciloscope? Soldering Iron?

Have you ever built a rather complex circuit before?

--ETA: The only commercial one I found in a quick search is a 4 band though you may find you love it in addition to your mixing panel, especially if you've never used one before. For $150, It offers far more in the way of features, low distortion, and S/N ratio than anything we could design quickly here for you, though opinions may vary, especially depending on your tech level.

RPQ160b Manual
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Thread Starter


Joined Dec 21, 2011
Thinking on terms of distortion and quality, I do kind of think the beginner-esque craftsmanship of my work would affect sound quality... I think it would just be more practical to buy a better mixer for like $350.

Thanks for the thoughts though, I'm just not well-versed enough to wrap my head around this sort of stuff yet lol. I'm a networking major, and electronics are fun, but that first reply made my head spin :)