# Parametric EQ

#### carl1988

Hi All,

This EQ frequency range is 500Hz-15KHz. How is that calculated?
I need to limit it to 3KHz-6KHz

*R41=6K8

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#### Markw4

Embedded links don't always work anymore. Don't know why. If you add attachment files in advanced mode then someone might be able to see what you are asking about.

#### carl1988

Here is the schematic:

#### Attachments

• Bell-EQ.jpg
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#### carl1988

Second EQ circuit

In this one , Q is either 1 or 2.4 (depending on the S16 switch)

How is that calculated? How can I achieve a Q of 0.5 (and maybe 2.6) ?

#### Attachments

• Bell-EQ-2.jpg
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#### Mark Tillotson

Active filter circuits come in many topologies, each with its own design equations. Its possible to work out from first principles using network analysis, though usually much easier to find the design equations by searching - here I'm not sure what topology that is, if you have more details or a name for the circuit that will help track it down, otherwise its Kirchoff's laws and lots of complex algebra.

#### carl1988

Thanks Mark,

This circuit belongs to A&H ML5000 mixing console.

#### MagicianT

Topology is Wien Bridge, freq. span is defined by C16 (C17) and R49+RV6A (R52+RV6B). Highest 1/ 2* PI()*R*C = 15kHz with 6.8 kOhm, and lowest 0.5kHz with 206.8 kOhm.

Q is depends on R123/R122 voltage divider in positive feedback loop, can't say more precise.

#### carl1988

Topology is Wien Bridge, freq. span is defined by C16 (C17) and R49+RV6A (R52+RV6B). Highest 1/ 2* PI()*R*C = 15kHz with 6.8 kOhm, and lowest 0.5kHz with 206.8 kOhm.

Q is depends on R123/R122 voltage divider in positive feedback loop, can't say more precise.

Thank you very much!