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Old 23rd March 2011, 02:23 AM   #1
c12mech is offline c12mech  United States
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Default Adding bands to an equalizer circuit?

If I were to build a 10 band EQ similar to this one:

Graphic Equalizer Circuit for 10 Frequency Bands

how would I make it a 20 band circuit? Is it just a matter of adding more of the same IC sections and components or is there more to it? I've looked around and don't seem to find a lot of info on building anything more than the 10 band EQ shown. I'm sure it is probably overkill but it is just something I want to try.

Any help would be appreciated.
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Old 23rd March 2011, 03:08 AM   #2
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Yes, you will parallel more filters. The "more to it" part is having to calculate the passive component values for the extra filters.
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Old 23rd March 2011, 03:39 AM   #3
c12mech is offline c12mech  United States
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Would you happen to know where I could find the formulas for the needed calculations? This is the part I am stuck on.
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Old 23rd March 2011, 06:50 AM   #4
C04pl is offline C04pl  France
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Hi
It may be not so easy to add more filters. You may know what width of band all of these filters are. If its 6db/oct then changing some another close freq filter may also make changes with another - just they will so close each other. To make true graphic multiband eq will be better idea to find 12 or 18 or even 24 db/oct eq. You need band stop/notch filters to be not close enough to make changes in neighbor frequencies. For example there pot sliders: 32, 45, 60 Hz... then 45 can make changes in both 32 and 60 Hz. This will be really unwanted thing.
Cheers
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Old 23rd March 2011, 08:09 AM   #5
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Quote:
Originally Posted by c12mech View Post
Would you happen to know where I could find the formulas for the needed calculations? This is the part I am stuck on.
Those opamps are known as Gyrators. This calculator should help. Worked great when I re-tuned the bottom 2 stages of a 5 band graphic EQ in a Technics receiver. 80 and 320 Hz was ridiculous. 25 and 180 Hz suits me better.

Guitar Pedals: Gyrator Filter Calculator

G
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Old 23rd March 2011, 02:16 PM   #6
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Go to Spectrum Analyzer and Equalizer Designs for more info. E
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