This 100mW stereo amplifier is designed to integrate with a mixer, or can be used independently or as a basis for a multi-box headphone amplifier (box 4 headphone amplifiers for example). It operates under a balanced power supply with a range from + / -9 V and + / -18 V.
The 100mW stereo amplifier based TL 082 circuit is based on the combination of op amp and an output stage (pseudo) two push-pull transistors, capable of delivering power to feed more than comfortable headphones, even if it at an average performance.
Input of both left and right channels will be carried out through a stereo female jack if you want to embed this amp in a box reserved for this purpose. Of course, this jack will not be necessary if the integration is made with your own mixer.
The amplification of around of 10 (20dB), is determined by the ratio of resistors R2 / R1 (left channel, top) and R10 / R9 (right channel, bottom). You can always change the report if you feel the need to. The presence of knobs for adjusting the input level, however, you should avoid changing the value of these resistors, the adjustment range to suit a wide variety of situations. The presence of the capacitor C1 in series with the resistor R1 (with R9 and C5) limits the DC gain to a value of 1. In this way, any DC voltage output (offset) will be minimal and will not risk damaging the headphone. You have indeed noted the absence of coupling capacitor output …
The diodes D1 to D4 compensate the threshold base-emitter junctions of transistors, and in combination with resistors R5, R6, R13 and R14 can set the base bias to a value that guarantees operation with minimal crossover distortion.
Circuit Notes:
- The resistors R3, R4, R11 and R12 can easily Show their value rise to 10 ohms. The power dissipated in these resistors should be 0.5 W at a minimum, I recommend the same to limit the use of models 1W.
- Many may agree transistors output: a pair of 2N1711 (NPN) + 2N2905 (PNP) will do just fine, and a pair of BC547 (NPN) + BC557 (PNP) or BC337 (NPN) BC327 + (PNP).
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