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.
increased up to 400mA if you want low distortions.
The power transistors are placed on the same side of printed circuit board, so that it can be mounted on a heatsink jointly with the thermistor. The heatsink must be large enough and have the thermal resistance of maximum 10K / W.
L1 has 20 turns with 0.8mm emailed copper, coiled over R21. C9 is a ceramic capacitor.
Guitar amp specifications
- frequency band (at 3dB/8Ω): 11Hz … 20kHz
- THD at 1kHz: 0.006% at 1W/8Ω/Ir = 400mA
- THD at 1kHz: 0.02% at Ir = 400mA
- THD at 1kHz: 0.02% at 65W/8Ω/Uin = 873mV
- THD at 1kHz: 0.006% at 80W/4Ω/Uin = 700mV