Electric Guitar Preamp Mixer and Line Driver

Posted on Feb 6, 2014

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
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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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