The circuit aims to produce a headphone amplifier that would use a single integrated circuit TDA2004 to perform all the necessary functions.
TerminologyTDA2004 – a class B dual audio power amplifier in multiwatt package specifically designed for car radio applications and stereo amplifiers due to its high current capability, low impedance loads drive, low noise, overrating chip temperature, high reliability, output AC short circuit to ground, low distortion, very low number of external components, very inductive load, load dump voltage surge, and very simple mounting system with no electrical isolation between the heatsink and the packageOperational Amplifier (Op-Amp) – a DC coupled high gain electronic voltage amplifier with differential inputs and usually a single outputCircuit Explanation
The design of the amplifier of the headphones consists of medium power operational amplifier with the possibility of driving low loads. The whole package of the circuit consists of two amplifiers. The pair of resistors R3 & R4 and R11 & R12 on each channel of the IC1 regulates the voltage gain of the circuit that would produce a 40 dB output. On the other hand, the combination of R12 & C2 and R13 & C15 is responsible for regulating the bandwidth for each unit which is limited to 22 KHz.
The impedance of the earphones is being adjusted by the resistors R5 and R10. In order to prevent annoying and unwanted noise to occur when the headphones are inserted onto the plug, the capacitors C9 and C12 and being discharged via resistors R6 and R9. With the provided values and configuration of all the components, the circuit will exhibit excellent characteristics such as satisfactory frequency response, low noise, and low distortion. The circuit can be maintained by a 15 V supply and a 150 mA current source. A suitable heatsink should be used in IC1 to ensure that the temperature will not increase excessively to avoid possible damage.
C3-10-11=100nF 100V MKT
|C6-15=3.3nF 100V MKT
IC1=TDA2004 in Heatsink
The headphone amplifier is mainly used to drive the small speakers of headphones, even those with high impedance but can be driven from low power audio sources. Although they are considered as a type of audio amplifier, they cannot be used with loudspeakers since they are built like miniaturized power amplifiers. They can also be found integrated in televisions, portable music players, and other electronic devices such as integrated amplifiers. In speakers that are self-powered in desktops or workstations, the preamplifier stage can be done by the headphone amplifier. The different digital and analog sound sources can be centrally controlled by the headphone amplifier. There are different designs that were manufactured with the use of cables like optical, coaxial, and Universal Serial Bus (USB), for digital inputs.