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Audio Power Amplifier Converter From Stereo to Mono
The circuit was constructed for the purpose of transforming a stereo power amplifier to mono where the two channels are bridged internally.Stereo – derived from the words stereophonic sound, refers to the reproduction of sound with the use of two or more independent channels via loudspeakers with symmetrical configuration, as a way to create an impression of hearing the sound from various directions like the natural hearing Mono – short for monaural or monophonic sound, refers to the unidirectional type of reproduction of sound using a single channel where all elements of the sound recording are directed using one amplifier and speaker combination TL074 – low noise JFET quad operational amplifier with features such as high slew rate, latch up free operation, compensated internal frequency, low harmonic distortion, protection from output short circuit, JFET input stage with high input impedance, low offset current and input bias, low noise, and wide common-mode and differential voltage range
The terms stereo and mono are often used to refer to amplifier connections. A stereo amplifier consists of two independent channels of audio signal where the signals produced have a specific level and phase relationship to each other while a mono amplifier has all the audio signals mixed together and routed via a single audio channel.
The operation of the circuit includes revering the phase of one power amplifier where the change in polarity results to 4 times of output power. The symmetric input of two channels is electronically balanced in the J1 connector where two types of XLR plugs are connected. The level of each stereo channel is regulated separately by the potentiometers VR1 and VR2 while being connected to switch S1a-b in the point 2. The two amplifiers are bridged by transferring S1a-b to point 1 where the level is regulated by VR1. At this stage, the R channel is suppressed while the L channel receives the signal. The phase will be simultaneously inverted within the region of IC1c to drive the second power amplifier of R channel with reverse polarity from L channel. The output will turn out to be positive from the final amplifiers.
The circuit feeds its output to the loudspeakers for the stereo. Obtaining a précised results requires the resistors of differential amplifiers input to be at 1% tolerance made of metal film potentiometers while having a good quality switches and capacitors. The circuit is being supplied by s stabilized 15V power. In the case of asymmetrical input, 0V is used with the negative inputs of signal J1/1 with L/mono and J1/5 with R. In this connection, the positive inputs J1/2 and J1/6 receives the asymmetrical signal entry.
The stereo to mono converter circuit may be applied with regards to the desire of the user. If the user chose the signals to be in stereo, the circuit may be used in most home theater circuits while mono is standard for hearing aids induction loops, telephone networks, and radiotelephone communications. Some stereo to mono converters are designed with potentiometers located at the rear panel, and is used for output gain adjustment to allow a normalized mono output from domestic stereo equipment with the use of preset potentiometers.