Voltage Controlled Amplifier Schematic

A simple linear voltage controlled amplifier can be constructed with one op amp and two jfets see the figure.

Voltage controlled amplifier schematic.

All available circuits have limitations and this article looks at the various techniques used. A vca voltage controlled amplifier attenuator is the heart of any compressor or peak limiter circuit and there are quite a few different approaches. The vca810 is a dc coupled wideband continuously variable voltage controlled gain amplifier. Assemble the circuit using a tl071 tl081 or lf351 op amp.

A current ilsc is inserted into this input which controls the gain of the device linerly. 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. 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 voltage controlled variable gain amplifier circuit is built with ic op amp type lm101.

Consequently a vco can be used for frequency modulation fm or phase modulation pm by applying a modulating signal to the control input. 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. Do not apply a dc voltage outside this range for the jfet could be damaged and remember. 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.

The amplifier can achieve an 80 db dynamic control range with less than 0 2. This voltage controlled amplifier circuit is simply an op amp having an additional input at pin 5. The voltage gain a for an op amp is very large greater than 10 5. Verify that that gain of the circuit can be varied between unity and 1 20 by varying vcover the range vto vc 0.

At some voltage level the entire signal is let through. A vco is also an integral part of a phase locked. A voltage controlled oscillator vco is an electronic oscillator whose oscillation frequency is controlled by a voltage input. 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.

The applied input voltage determines the instantaneous oscillation frequency. A voltage controlled amplifier can be realised by first creating a voltage controlled resistor vcr which is used to set the amplifier gain. Vcrs manufactured in this way can be obtained as. 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.

The 2n5457 works as a voltage variable resistor having an rds on max of 800 ohms.