Building a pre-amplifier with 3 band equalizer for bass.

[space_astronaut]

Hello guys, I am a newcomer here. The last couple of days I was trying to understand how the 3 equalizer band works, however I've been struggling to understand the principle behind the scenes to calculate the bass, mid and treble frequencies. The formula to obtain the frequency is f = 2.Pi.C.R but the numbers don't match. I would like to build a bass pedal or, a more challenging project, a preamplifier considering this type of equalizer with a couple of 2SC5200/2SA1943.

The first diagram that I am trying to calculate the frequencies is:

The diagram developer told that the bass, mid and treble are, respectively, 28Hz, 10.2kHz and 18kHz.

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The second diagram that I am trying to figure out is more complicated because it uses two TL072, and this is the one that I am more interested in:

In the second case the bass, mid and treble frequencies are, respectively, 100Hz, 800Hz and 4.5kHz. In this particular diagram, which Resistors and Capacitors are responsible for the bass frequency and how could I change those values for 80Hz, 500Hz and 2kHz ? I would like to implement the second diagram to a bass pedal or pre-amplifier.

Thank you for your help.

 

[BuddytheReow]

The first diagram, at least from what I’m told, is more interactive in terms of the mid control. It can easily overpower the other two. The fix, I think, is to stick a resistor either before or after C9.

The second diagram separates the mid control entirely as it own stage to make all 3 controls independent.

Try fooling around TSC in the web in addition to breadboarding to tweak the values. You’ll need to search for an active baxandall or James tonestack. Chuck also wrote some boneyard articles about EQ which will help. They’re a little older so you’ll have to dig through a number of pages to get to them.