# Active filter/ Tone control

Discussion in 'The Projects Forum' started by Amagic, Jul 18, 2007.

1. ### Amagic Thread Starter New Member

Jul 18, 2007
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Hi does anybody know how to read the circuit attached, I'm trying to find out how to work out the max and min Gain for each circuit,

the part that is comfusing me the most is the capacitor. i'm trying to find out how the circuits reacts to various frequecies

If anybody can help i would be very greatful

Thanks

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2. ### cumesoftware Senior Member

Apr 27, 2007
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The circuits are to small to look at. The capacitor has a high impedance (AC resistance) to low frequencies and a low impedance at high frequencies. But I notice that are connections made wrong. Only the feedback network should use the "-" input. The signal should be fed at "+" input if I recall. Unless you want to make an inverting circuit.

3. ### hgmjr Moderator

Jan 28, 2005
9,030
214
I too found the images too small to read. Hopefully you can take another shot at attaching the images so that we can address your questions regarding the transfer functions of your circuits.

hgmjr

Apr 26, 2005
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5. ### nomurphy AAC Fanatic!

Aug 8, 2005
567
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You can combine into a single op amp, if you also use a low source impedance pre-driver to the tone controls. A quad op amp (TL074) works well for stereo. See attached:

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6. ### nomurphy AAC Fanatic!

Aug 8, 2005
567
12
Here are the equations:

BASS (assumes R24 > R22)
~38.1 Hz = fL = 1 / 2pi*R24*C23

~284Hz = fLB = 1 / 2pi*R22*C23

~10 = AvB = 1 + (R24 / R22)

TREBLE (assumes R26 > R22+R23+2R25)
~8.8K = fH = 1 / 2pi*C25*R23

~856Hz = fHB = 1 / 2pi*C25*(R22+R23+2R25)

~10.3 = AvT = 1 + [(R22 + 2R25) / R23]