AmplifierCircuits

This is a medium power guitar amplifier is recommended especially for portable amplifier. The amplifier is a combination between a simple integrated audio driver, LM391-80 and a stage of output power designed contratemps with bipolar transistors. Thermistor NTC, which is in temperature contact with output power transistors, allows to separate AO LM391 power stage when it heats too much. The start of the thermal protection is at a NTC flow current NTC of approximately 200uA. Electrolytic condenser asure a “smooth start” to remove clicks that may occur when connecting the amplifier. It can happen that the protection can be too sensitive, in that case certain adjustments are admitted in the value of R4 or thermistor. The standby current can be adjusted with P1. This potentiometer is initially 0 and then is adjusted to achieve a current of 50mA. Current can be increased up to 400mA if you want low distortions. The power transistors are placed on the same side of printed circui...

General Description This design adopts a well established circuit topology for the power amplifier, using a single-rail supply of about 60V and capacitor-coupling for the speaker(s). The advantages for a guitar amplifier are the very simple circuitry, even for comparatively high power outputs, and a certain built-in degree of loudspeaker protection, due to capacitor C8, preventing the voltage supply to be conveyed into loudspeakers in case of output transistors' failure. The preamp is powered by the same 60V rails as the power amplifier, allowing to implement a two-transistors gain-block capable of delivering about 20V RMS output. This provides a very high input overload capability. Features: Sensitivity: 35mV input for 40W 8 Ohm output 42mV input for 60W 4 Ohm output Frequency response: 50Hz to 20KHz -0.5dB; -1.5dB @  40Hz; -3.5dB @ 30Hz Total harmonic distortion @ 1KHz and 8 Ohm load: Below 0.1% up to 10W; 0.2% @ 30W Total harmonic distortion @ 10KHz a...