3 Channel Equalizer - Bandpass 4th Order

[S!nn3r]

Hello all.

i would appreciate if anybody could help me with a circuit design for an Equalizer. i should realize the board for a connection with STM32F411 Discovery (it would be a second part of task).

It is an example for a study. Recently i received this project to realize, original text is in German but there are details:

3 Channel Equalizer:

Bandpass for frequencies 100Hz, 1kHz, 10 kHz
those frequencies should be gained trough potentiometer from +12dB to -12dB
Band-passes should be min 4th order
as an input source should be used BNC-socket
output signal to be transmitted to an existing AD channel
simulation in Multisim or Spice

i added a picture of an expected gain graph (potentiometer should limit gain between +12dB and -12dB)

Thanks for help
i guess that the way of circuit design is not as much complicated for someone who already has experience with this tasks

 

[Harald Kapp]

Welcome to ep.

From the description I take it an analog solution is expected. A fourth order bandpass filter is most easily made up from 2*2nd order bandpass filters. In the frequency range you're dealing with operatinal amplifiers are well suited to the task. Any search engine will turn up basic opamp based 2nd order bandpass filters plus calculators to tell you which components to use.
There are different topologies how a band pass filter can be realized. It's up to you to chose the one most fitting your application.
One important parameter is missing from your task description: bandwidth.
Without this parameter you have unlimited possibilities to realize a band pass that fits center frequency and order.

 

[S!nn3r]

Thanks. I just want to add it is an active filter and i have many examples how to realize it. Bandwidth is an optional in this task. Calculating is also not such a big problem. But I lost myself in realizing gain +12 to -12dB.
How to add a potentiometer in this circuit (uploaded file) to control a gain but not with additional op amps.
This would be 1 Channel example. Gain is missing... positive to negative... it should not be complicated but i am not thinking in the right direction

 

[Harald Kapp]

realizing gain +12 to -12dB.

Forget for a moment theband pass. How and where would you add a pot in an audio amplifier to realize a settable gain?
Also note that +-12 dB is one way to express the gain change. It could also be expressed as 0 dB...-24 dB, depending on the default gain of the amplifier.