Here is the circuit
diagram of a guitar preamplifier that would accept any standard guitar
pickup. It is also versatile in that it has two signal outputs. A
typical example of using a pick-up attached to a guitar headstock is
shown in Fig. 1. The pickup device has a transducer on one end and a
jack on the other end. The jack can be plugged into a preamplifier
circuit and then to a power amplifier system. The pickup device captures
mechanical vibrations, usually from stringed instruments such as guitar
or violin, and converts them into an electrical signal, which can then
be amplified by an audio amplifier. It is most often mounted on the body
of the instrument, but can also be attached to the bridge, neck,
pick-guard or headstock.
The first part of this preamplifier circuit shown in Fig. 2 is a
single-transistor common-emitter amplifier with degenerative feedback in
the emitter and a boot-strapped bias divider to secure optimal input
impedance. With the component values shown here, the input impedance is
above 50 kilo-ohms and the peak output voltage is about 2V RMS.
Master-level-control potentiometer VR1 should be adjusted for minimal
distortion. The input from guitar pickup is fed to this preamplifier at
J1 terminal. The signal is buffered and processed by the op-amp circuit
wired around IC TL071 (IC1). Set the gain using preset VR2. The circuit
has a master and a slave control. RCA socket J2 is the master signal output socket and socket J3 is the slave.
It is much better to take the signal from J2 as the input to the
power amplifier system or sound mixer. Output signals from J3 can be
used to drive a standard headphone amplifier. Using potentiometer VR3,
set the slave output signal level at J3. House the circuit in a metallic
case. VR1 and VR3 should preferably be the types with metal enclosures.
To prevent hum, ground the case and the enclosures. A well-regulated 9V
DC power supply is crucial for this circuit. However, a standard 9V
alkaline manganese battery can also be used to power the circuit. Switch
S1 is a power on/off switch.