Rangkaian Low pass Filter aktif

type='html'>frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter when used in audio applications. A low-pass filter is the opposite of a high-pass filter, and a band-pass filter is a combination of a low-pass and a high-pass.

The concept of a low-pass filter exists in many different forms, including electronic circuits (like a hiss filter used in audio), digital algorithms for smoothing sets of data, acoustic barriers, blurring of images, and so on.

in the image below in the show Rangkaian Aktif low pass filter using op amp lm 741:

Skema rangkaian Low pass Filter aktif

In the operational amplifier circuit shown in the figure, the cutoff frequency (in hertz) is defined as:


or equivalently (in radians per second):


The gain in the passband is


and the stopband drops off at −6 dB per octave as it is a first-order filter.


Sometimes, a simple gain amplifier (as opposed to the very-high-gain operation amplifier) is turned into a low-pass filter by simply adding a feedback capacitor C. This feedback decreases the frequency response at high frequencies via the Miller effect, and helps to avoid oscillation in the amplifier. For example, an audio amplifier can be made into a low-pass filter with cutoff frequency 100 kHz to reduce gain at frequencies which would otherwise oscillate. Since the audio band (what we can hear) only goes up to 20 kHz or so, the frequencies of interest fall entirely in the passband, and the amplifier behaves the same way as far as audio is concerned.

Rangkaian Loudness Aktif

type='html'>

To get good audio reproduction at different listening levels, a different tone-setting controls should be necessary to suit the well known behavior of the human ear. In fact, the human ear sensitivity varies in a non-linear manner through the entire audible frequency band, as shown by Fletcher-Munson curves.

A simple approach to this problem can be done inserting a circuit in the Preamplifier stage, capable of automatically varying the frequency response of the entire audio chain in respect to the position of the control knob, in order to keep ideal listening conditions under different listening levels .

Fortunately, the human ear is not too critical, so a rather simple circuit can provide a Satisfactory performance through a 40db range.

Skema Rangkaian Loudness Aktif

List Component Of Loudness Aktif

P1______________10K Linear Potentiometer (Dual-gang for stereo)

R1,R6,R8_________100K 1/4W Resistors
R2______________27K 1/4W Resistor
R3,R5____________1K 1/4W Resistors
R4______________1M 1/4W Resistor
R7______________20K 1/2W Trimmer Cermet

C1______________100nF 63V Polyester Capacitor
C2______________47nF 63V Polyester Capacitor
C3______________470nF 63V Polyester Capacitor
C4______________15nF 63V Polyester Capacitor
C5,C9____________1µF 63V Electrolytic or Polyester Capacitors
C6,C8____________47µF 63V Electrolytic Capacitors
C7______________100pF 63V Ceramic Capacitor

IC1_______________TL072 Dual BIFET Op-Amp

SW1________________DPDT Switch (four poles for stereo)

The circuit is shown with SW1 in the "Control-flat" position, ie without the Automatic Loudness Control. In this position the circuit acts as a linear Preamplifier stage, with the voltage gain is set by means of Trimmer R7. Switching SW1 in the opposite position the circuit becomes an Automatic Loudness Control and its frequency response varies in respect to the position of the control knob by the amount shown in the table below. C1 boosts the low frequencies and C4 boosts the higher ones. Maximum boost at low frequencies is limited by R2; R5 do the same at high frequencies.

Rangkaian 2 line Crossover Aktif

type='html'>

Rangkaian 2 line Crossover Aktif

The electronic crossover featured here is an 18dB / octave unit, and has the crossover frequency centred on 300Hz.

Skema Rangkaian 2 line Crossover Aktif

The picture above shows the circuit diagram, and the NE5532 dual op-amp is used. This circuit can be operated from the same power supply as the Audio Preamp, featured elsewhere on these pages. Other dual opamps may also be used, depending on your preference. The input is buffered by U1a (the second channel can use the other half of the op-amp), and fed to the two filter networks. Each filter is a 3rd order section, and has a gain of 2. The output of each section is fed (via a 1uF polyester capacitor) to the level of control and output buffer stage. In use, the output of the Preamplifier is fed to the input of the crossover network, and the outputs are fed to their respective amplifiers.


Be careful when adjusting the level of controls, since it is easy to create a mismatch in levels between the amplifiers. I suggest that the controls be mounted on the rear panel, with their shafts cut off really short, and a slot cut into the end with a hacksaw. Once the adjustment is made, it should not require further changes in use. Make sure that the power amplifier volume controls (if fitted) are turned fully up, and try to set the crossover controls so somewhere between midway and 75%. This ensures plenty of scope for getting the levels right, and will Ensure that the preamp settings are not radically different from their "pre-biamp" days.
.