HEADPHONE_AMPLIFIER_FOR_GUITARS

Published:2009/7/12 23:45:00 Author:May | From:SeekIC

From the hard distortion provided by U1-d and D1 and D2 to the stereo imaging accomplished by U2, this is a guitarist's dream come true. Note that there is no power switch in the circuit; J1 turns on the unit whenever an instrument cable is plugged in.The main components in the circuit are two LM324 quad op amp ICs (U1 and U2) and two LM386 power amp ICs (U3 and U4). The inputs to U1 and U2 are biased to a little less than half the power-supply voltage by resistors R10 and R11. Capacitors C1 and C2 filter the power-supply and bias voltages. J1 turns on the amplifier when the input plug is inserted. When an audio signal from an instrument is input through J1, the signal is fed through coupling capacitor C3 to the tone-controlcircuit composed of U1-c, R2, R4, and C4. Frequencies above 1 kHz are amplified or attenuated depending on the position of potentiometer R4, which is the tone control. Resistor R2 and capacitor C4 filter unwanted high frequencies. Audio level and overdrive are controlled by potentiometer R9; with that level control adjusted to full volume, the circuit's final amplifiers are overdriven to produce a soft distortion effect. To prevent any unwanted dc swishing noise, a coupling capacitor, C8, is used.Switch S1 toggles between the clean and distorted signals. When S1 is on the CRUNCH setting, diodes D1 and D2 and U1-d produce a distortion effect by clipping the amplified signal at 0.7 V. Frequencies below 160 Hz are attenuated by R5 and C6. The amount of gain or fuzz is controlled by R7 and potentiometer R6, and resistor R8 adjusts the distortion level to match the tone-control level.



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