EQUALIZER

[madbassist82]

ok im building my second tube amp... but this one im want to put an EQ on so i can better choose my tone... its a bass amp so its in the lower frequencies my question is this in the circuit i link to below how do you change the the frequency that gets alter? i know its a cap and resistor controlled type of deal but whats the math or theory that it utilizes. i basically want a twenty band eventually for alteration all or most frequencies in the bass and mid spectrums... so basically how do i change the frequencies controlled in this schematic ten band eq

[Steve Conner]

Read this carefully Simple, Easy Parametric and Graphic EQ's, Plus Peaks and Notches - it explains the theory and gives example circuits for graphic and parametric EQs.

In your schematic, IC1B, IC1C, etc, are gyrators as explained in the above document. I think. It's different to the usual graphic EQ circuit, and I've never seen it before: maybe it uses notch filters instead of gyrators.

But note that the pairs of capacitors (C1/C2, C3/C4, etc) always have a 10:1 ratio. A safe bet would be to change these values while maintaining the 10:1 ratio, the frequency should change in proportion.