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This is a Simple Project of Passive Sub woofer filter Circuit Diagram . This circuit not required power supply because is a simple low frequency passive filter. It could be useful if you want to drive an extra sub-woofer from your stereo system.  Passive Sub woofer filter Circuit Diagram The circuit filters the frequency ranges above the 150Hz. The schematic is calculated to work with a 50 watts audio amplifier, but can be used with higher powers as well. The frequency can be adjusted with 2k2 potentiometer from 50 Hz to 160 Hz.

Using two op amps, this filter is designed for second-order response. It has a bandpass of 300 to 3400 Hz, for applications in speech or telephone work. 300-3400 Hz Second Order Speech Filter Schematic 

A notch for a narrow frequency band of a few per cent or even less normally requires close-tolerance components. At least, that’s what we thought until we came across a special opamp IC from Maxim. In filters with steep slopes, the component tolerances will interact in the complex frequency response. This effect rules out the use of standard tolerance components if any useful result is to be achieved. The circuit shown here relocates the issue of the value-sensitive resistors that determine the filter response from ‘visible’ resistors to ready available integrated circuits which also make the PCB layout for the filter much simpler. The operational amplifiers we’ve in mind contain laser-trimmed resistors that maintain their nominal value within 1‰ or less. For the same accuracy, the effort that goes into matching individual precision resistors would be far more costly and time consuming. The desired notch (rejection) frequency is easily calculated for both R-C sections shown in Figure 1....

Simple Universal Active Filter Circuit Diagram . The circuit as shown gives the bandpass operation the transfer function calculated from FBP(s) = where = 1 + s/Qo>0 + s2/w02. The cut-off frequency, 0, and the Q-factor are given by 0 = g/C and Q = gR/2 where g is the trans conductance at room temperature. Interchanging the capacitor C with the resistor R at the input of the circuit high-pass operation is obtained.   Simple Universal Active Filter Circuit Diagram   A low-pass filter is obtained by applying two parallel connections ctf R and C as shown in Fig. 2. The low-pass operation may be much improved with the circuit as given in Fig. 3. Here the gain and Q may be set up separately with respect to the cut-off frequency according to the equations Q = 1/fB = 1 + R2/R!, A = Q2 and 0 = g ffi/C.

This circuit uses a switched capacitor filter IC from National Semiconductor to filter signals with frequencies higher than the 3KHz needed for voice audio. The schematic includes an audio amplifier that is designed to drive a standard audio head phone.  The circuit is described in more detail in the receiver section of Dave Johnson's Handbook of Optical Through the Air Communications.(this link is off-site)  3khz Low Pass Filter and Audio Amplifier Circuit Diagram  

SEMICONDUCTOR FMS6363 LOW COST VIDEO FILTER ELECTRONIC DIAGRAM The FMS6363 Low Cost Video Filter (LCVF) provides 6dB gain from input to  output. In addition, the input will be slightly offset to optimize the output driver performance. The FMS6363 provides an internal diode clamp to support AC-coupled input signals. If the input signal does not go below ground, the input clamp will not operate. This allows DAC outputs to directly drive the FMS6363 without and AC coupling capacitor (usually 220 ?F). The offset is held to the minimum required value to decrease the standing DC current into the load.

In communications receivers and microphone amplifiers for transmitting equipment, there is frequently a need for a narrow, low-frequency band-pass filter that lets only the voice band through. This band is usually defined to be the portion of the audio frequency spectrum between approximately 300 Hz and 3300 Hz. In order to implement such a filter, we have calculated the values for two fifth-order Butterworth filters having these corner frequencies and connected them in series. The result is a band-pass filter for the desired pass-band with a skirt steepness of 100 dB/decade.  The first opamp (IC1) acts as a buffer. Speech Filter Image : The circuit can be powered by a unipolar supply voltage between 5 V and 18 V, which is a broad enough range that it should always be possible to find a suitable voltage when building the filter into existing equipment. The current consumption of the filter is only a few milliampères, which should rarely pose a problem. There is fairly wide selection ...

Low pass filter is a circuit to filter freq dirty from an fm transmitter. so we get a clean signal. and can maximize the output power generated from the booster. low pass filter is capable to 150 watts. in this post . file [lay] that can only be opened with software sprint layout. for those interested please download here.

First order Active High Pass Filter Calculator Enter the Value of R1: in ohms Enter the Value of R2: in ohms Enter the Frequency of Input signal: in Hz Enter the cutoff Frequency: in Hz Voltage gain:

FSK Frequency-Shift Keying is a form of frequency modulation in which the modulating signal changes the output frequency. between predetermined values​​. If problems arise in FSK demodulation signal is shown using this filter. The Frequency-Shift Keying filter is very simple and can be built into a phone plug. Filter FSK Circuit Diagram The diagram shows a low-pass filter made ​​of R1 and C2. This filter has a cutoff frequency. about 1.6 KHz. Once the "0" and "1" signals from FSK tones are sent as 1.2 kHz and 2.4 kHz respectively filter removes all the undesired signals. Both D1 and D2 ensure that the FSK signal is limited to about + / - 600 mV amplitude. It can be connected to a speaker or headphone output. components C1 = 0.0082 C2 = 0.018 R1 = 5.6kΩ D1 = D2 = 1N4148