The circuit was designed to create a balance input device that would provide an adjustment of gain and volume while having a symmetrical electronic input.NE5532 – an internally compensated low noise dual operational amplifier with features such as full power bandwidth up to 140 KHz, input noise voltage of 8 nV, common mode rejection ratio, 9 V/us slew rate, high DC voltage gain, 32 V peak to peak voltage swing, wide supply voltage range from 3 V to 12 V, unity gain bandwidth at 10 MHz, and internal frequency compensation TL072 – a low noise JFET input operational amplifier with features such as common-mode input voltage range, high slew rate, operation without latch up, compensated internal frequency, high input impedance at the JFET input stage, low noise,low total harmonic distortion, protected from output short circuit, low input bias and offset currents, wide common-mode and differential voltage ranges, and low power consumption The operation of the circuit includes the adjustment of the gain with the use of 10K ohms potentiometer RV1 while the level of the signal or the volume is regulated with the 47K ohms potentiometer RV2. In order to prevent unwanted noises from being absorbed during the regulation of gain, the potentiometer RV1 should be of good quality. Alternatively,the potentiometers can be replaced by other material like a set of resistors that requires enough testing and adjustment to meet the desired output.The integrated circuits used is not necessarily the compulsory to use because other types of models can also be chosen for as long as they possess similar characteristics as what is recommended in this circuit like low noise, low distortion, and other convincing factors. From the values involved in the circuit, the resistance is approximately 2K ohms. This amount is sufficient for low level of signal to be amplified like the one coming from a microphone. An attenuation of signals occurs during the presence of high level signals. In this case, the adjustment of gain with the operation of RV1 is at its boundaries where the resistance decreases for the two input section.
Figure 2
The basic concept of the balance input with gain and volume circuit may be applied in the use of preamplifiers where some advanced designs are coming with remote control that has volume control, input select and mute functions. They are mainly used in home theater systems to provide quality sounds since they are able to adjust the gain and the volume of the output.Source:users.otenet.gr/~athsam/balance_with_gain.htm