Voltage Controlled Amplifier Schematic

Assemble the circuit using a tl071 tl081 or lf351 op amp.

Voltage controlled amplifier schematic.

A current ilsc is inserted into this input which controls the gain of the device linerly. The vca810 is a dc coupled wideband continuously variable voltage controlled gain amplifier. The applied input voltage determines the instantaneous oscillation frequency. All available circuits have limitations and this article looks at the various techniques used.

The voltage controlled variable gain amplifier circuit is built with ic op amp type lm101. When the output voltage exceeds the supplied power the op amp saturates this means that the output is clipped or maxed out at the supplied voltages and can increase no further. A voltage controlled oscillator vco is an electronic oscillator whose oscillation frequency is controlled by a voltage input. A simple linear voltage controlled amplifier can be constructed with one op amp and two jfets see the figure.

A vca voltage controlled amplifier attenuator is the heart of any compressor or peak limiter circuit and there are quite a few different approaches. Apply a sine wave to the input and a negative dc voltage to vc. Do not apply a dc voltage outside this range for the jfet could be damaged and remember. Vcrs manufactured in this way can be obtained as.

The op amp amplifies the difference between the two inputs v p and v n by a gain a to give you a voltage output v o. The higher the control voltage the more signal is passed. The device provides a differential input to single ended output conversion with a high impedance gain control input used to vary the gain over a 40 db to 40 db range linear in db v. This voltage controlled amplifier circuit is simply an op amp having an additional input at pin 5.

At some voltage level the entire signal is let through. The vcr is one of the numerous interesting circuit elements that can be produced by using a jfet junction field effect transistor with simple biasing. The amplifier can achieve an 80 db dynamic control range with less than 0 2. A voltage controlled amplifier can be realised by first creating a voltage controlled resistor vcr which is used to set the amplifier gain.

Verify that that gain of the circuit can be varied between unity and 1 20 by varying vcover the range vto vc 0. The voltage gain a for an op amp is very large greater than 10 5. The 2n5457 works as a voltage variable resistor having an rds on max of 800 ohms. Because the differential voltage on the lm101 is within the low mv range the 2n5457 jfet will have linear resistance over several decades of resistance.

Thus by inserting an audio signal 10 mv within pin 2 and 3 and with controlling the current on pin 5 the amount of the signal output pin 6 is controlled.