Mutchus

This circuit is a five-band graphic equalizer mono, covering the audio frequency of 55Hz, 270Hz, 1kHz, 3.5 kHz and 12kHz. The basic difference between this graphic equalizer with other circuits, is instead of CI it uses transistors, the power supply is also special is +24 V 0-24v DC, this ensures low distortion and greater margins overload.   Simple 5 Band Graphic Equalizer Circuit Diagram List of components R1-4-37 = 330Kohms R2-7 = 2.2Kohms R3 = 120Kohms R5-6 = 6.8Kohms R8 to 12 = 1.8KOHMS R13 to 15 = 200Kohms R16 = 180Kohms R17 = 150Kohms R18 = 1.5KOHMS R19 to 22 = 1Kohms R23 to 27 = 220Kohms R28 to 32 = 15Kohms R33 = 10Kohms R34 = 15Mohm R35-38 = 220 ohms 1W R36 = 100 ohms C1-3 = 40V 1uF C2 = 68PF 100V C4 = 220uF 63V C5 = 1uF 100V C6 = 220nF 100V C7 = 47nF 100V C8 = 15NF 100V C9 = 5.6nF 100V C10 = 47nF 100V C11 = 15NF 100V C12 = 4.7nF 100V C13 = 1.5nF 100V C14 = 470pF 100V C15 = 68PF 100V C16-19 = 100nF 100V C17-20 = 470uF 40V C18 = 4.7uF 63V RV1 until RV5 = 50Kohms Lin. Q1 to ...

Audio graphic equalizers are very common as commercial products (for Hi-fi, car audio and stage use) but circuits for them are very rarely published. I didn't design this one but it's really very simple. The details shown are for a 7 band but the principle can be extended to almost any number of bands - if you can find accurate enough components.  Only one gyrator stage is shown: all 7 gyrators are the same circuit, only the capacitors change, as shown in the chart. I have shown three of the seven faders to show where they go.  A gyrator is a circuit using active devices and transistors to simulate an inductor. In this case the gyrator is the transistor acting with R1, R3 and C2. It could just as easily be a unity gain op-amp.  The circuit includes three formulae: one which gives f, the the centre frequency of the band. The second shows how the Q is related to the capacitor ratio. The third shows the impedance presented by the circuit. Note that this includes 3 terms, th...