Electric Guitar Preamp Mixer and Line Driver

  
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Depending on its design an electric guitar may have anything from one to six pickup elements. Classic (acoustic) guitars could also benefit from one or more retro- ¬tted pickups. Each pickup has a specific sound depending on the type of sensor and the location on the instrument. When a guitar has more than one pickup these can be connected togeth
Electric Guitar Preamp Mixer and Line Driver - schematic

er with or without additional components. However it is preferable for each pickup signal to be buffered individually. These buffered and possibly amplified signals should be level-adjusted in order to produce the desirable effect (or sound`). After that they are mixed and sent to the next stage of the audio processing equipment. Most guitarists agree that pickup elements cannot drive cables longer than about 6 feet without risking significant signal degradation. Guitar pickups typically require a load resistance above 50 k © and sometimes higher than 200 k ©, hence a preamplifier/buffer is often inserted, whose main function is not high gain but to enable cables between 10 and 30 feet to be connected representing a capacitance between 90 and 180 pF/m. In the circuit shown here, each pickup has its own input buffer with a transistor con ¬gured as an emitter follower. Each stage has a gain slightly lower than unity. This is not an issue because most pickups provide significant signal levels, typically well over 200 mVpp. The input resistance of the ¬rst stage exceeds 200 k ©, which is appropriate for most inductive pickups on the market. If higher input resistance is needed the 1-M © resistors marked with asterisks could be omitted, and the 720-k © ones may be increased to 1. 2 1. 5 M ©. This will raise the stage`s input resistance to around 500 k ©. To ensure the highest possible undistorted signal can be developed at the...



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