Mini Guitar/Bass Amplifier

Output power: 6W into 4 Ohm load

FET input stage - Passive Tone Control

Circuit diagram:

Mini Guitar/Bass Amplifier


P1______________1M  Linear Potentiometer
P2____________100K  Log Potentiometer

R1_____________68K  1/4W Resistor
R2____________470K  1/4W Resistor
R3______________2K7 1/4W Resistor
R4______________8K2 1/4W Resistor
R5____________680R  1/4W Resistor
R6____________220K  1/4W Resistor
R7_____________39R  1/4W Resistor
R8______________2R2 1/4W Resistor
R9____________220R  1/4W Resistor
R10_____________1R  1/4W Resistor
R11___________100R  1/2W Resistor
R12_____________1K5 1/4W Resistor

C1____________100pF  63V Polystyrene or Ceramic Capacitor
C2,C5,C9,C14__100nF  63V Polyester Capacitors
C3____________100µF  25V Electrolytic Capacitor
C4_____________47µF  25V Electrolytic Capacitor
C6______________4n7  63V Polyester Capacitor
C7____________470pF  63V Polystyrene or Ceramic Capacitor
C8______________2µ2  25V Electrolytic Capacitor
C10___________470µF  25V Electrolytic Capacitor
C11____________22nF  63V Polyester Capacitor
C12__________2200µF  25V Electrolytic Capacitor
C13__________1000µF  25V Electrolytic Capacitor

D1______________3mm  red LED

Q1____________BF245 or 2N3819 General-purpose N-Channel FET

IC1_________TDA2003 10W Car Radio Audio Amplifier IC 

SW1,SW2________SPST toggle or slide Switches

J1____________6.3mm Mono Jack socket
J2____________6.3mm Stereo Jack socket (switched)
J3_____________Mini DC Power Socket

SPKR__________4 Ohm Car Loudspeaker 100 or 130mm diameter


Tiny, portable Guitar Amplifiers are useful for practice on the go and in bedroom/living room environment. Usually, they can be battery powered and feature a headphone output.
This project is formed by an FET input circuitry, featuring a High/Low sensitivity switch, followed by a passive Tone Control circuit suitable to Guitar or Bass. After the Volume control, a 6W IC power amplifier follows, powered by a 12-14V dc external supply Adaptor or from batteries, and driving a 4 Ohm 10 or 13cm (4"/5") diameter car loudspeaker. Private listening by means of headphones is also possible.


Technical data:

Output power (1KHz sinewave):
6W RMS into 4 Ohm at 14.4V supply
50mV RMS input for full output
Frequency response:
25Hz to 20kHz -3dB with the cursor of P1 in center position
Total harmonic distortion:
0.05 - 4.5W RMS: 0.15% 6W RMS: 10%
Tone Control Frequency Response:
Tone Control Frequency Response