Crystal pickup pre-amplifier circuit

Description: A preamplifier that operates on a single supply and is suitable for high-impedance crystal pickups is presented here. The circuit functions as a non-inverting AC amplifier, with the gain determined by the feedback resistor R4; a smaller R4 results in lower gain. The low-frequency roll-off characteristics are influenced by capacitor C3. A voltage divider network composed of resistors R1, R2, and R5 provides a DC bias of approximately half the supply voltage. Additionally, R5 and capacitor C2 form a supply line filter to minimize hum levels and reduce the likelihood of noise interference when the preamplifier is powered from a shared power supply.

The described preamplifier circuit is designed to enhance the output signal from high-impedance crystal pickups, which are commonly used in applications such as musical instruments. The non-inverting configuration allows for a straightforward amplification of the input signal while maintaining phase integrity. The gain of the amplifier is adjustable through the feedback resistor R4; this design offers flexibility in tuning the signal amplification according to specific requirements.

Capacitor C3 plays a critical role in defining the low-frequency response of the amplifier. By selecting an appropriate value for C3, the designer can control the point at which the amplifier begins to attenuate lower frequency signals, thus tailoring the circuit's response to suit the characteristics of the pickup being used.

The voltage divider network, consisting of resistors R1, R2, and R5, is essential for establishing a stable DC bias at approximately half the supply voltage. This biasing ensures that the amplifier operates within its optimal range, preventing distortion and allowing for a clean amplification of the audio signal.

Furthermore, the combination of resistor R5 and capacitor C2 serves as a low-pass filter, which is crucial in minimizing unwanted hum and noise that may arise from power supply fluctuations or interference. This filtering capability is particularly important in environments where multiple devices share a common power supply, helping to ensure that the preamplifier delivers a high-quality audio signal free from unwanted artifacts.

Overall, this preamplifier circuit is a well-designed solution for enhancing the performance of high-impedance crystal pickups, providing adjustable gain, stable biasing, and effective noise reduction.A preamplifier operating on a single supply and suitable for use with high impedance type crystal pickups is shown here. The circuit is basically a non-inverting AC amplifier in which the gain is dependent on the feedback resistor R4.

The smaller is the R4, the lower will be the gain. The low frequency roll off characteristics are decided by C3. Volta ge divider network comprising of R1, R2 and R5 provide a DC bias of about half the supply voltage R5 and C2 from a supply line filter to reduce the hum level as well as to reduce the chances growling  when the preamplifier is operated from common power supply.