This is a basic amplifier circuit for beginners. These active speakers are to be portable, Lo-Fi, and provide up to 0.3W of RMS power for each channel. This circuit can be powered using 4 AA batteries of using a wall adaptor (6V DC, 150mA minimum). S1 serves to choose power from batteries or from the adaptor, D is to protect from reverse polarity from the adaptor. D does not protect from reverse current from batteries, since a normal rectifier diode would cause a voltage drop, reducing the functioning time in case of the circuit being fed using 1.2V batteries.
The overall gain of this circuit is 26dB. To compensate poor bass response from the speakers, this circuit has a 6dB "bass boost" (treble attenuation actually, >1KHz).
FTE2 corresponds to the right channel. FTE1 corresponds to the left channel and is installed in a separate box, apart from FTE2 and the circuit. The connection between FTE2 and the amplifier circuit can be made using a standard RCA/RCA plug.
View attachment CSA300mW.pdf
List of components (version 1):
B1-4 - 1.2V (Ni-CD or Ni-MH) or 1.5V (carbon-zinc or alkaline) battery;
C1 680µF electrolytic capacitor (10V) (typo);
C2/3 100nF polyester capacitor (63V);
C4/9 2.2µF electrolytic capacitor (6,3V);
C5/10 47µF electrolytic capacitor (10V);
C6/11 33nF polyester capacitor (63V);
C7/12 47nF polyester capacitor (63V);
C8/13 220µF electrolytic capacitor (10V);
D 1N4001 rectifier diode (D1 in the diagram, my mistake);
FTE1/2 2-1/2 inch speaker (8Ohm, 0.5W);
IC1/2 LM386 audio power amplifier;
R1 10K double gang potenciometer (10% tol., 1/8W);
R2/5 4,7K carbon resistor (5% tol., 1/8W);
R3/6 15K carbon resistor (5% tol., 1/8W);
R4/7 10Ohm carbon resistor (5% tol., 1/8W);
S1 SPDT switch;
S2 SPST switch.
View attachment CSA300mW(2).pdf
List of components (version 2):
B1-4 - 1.2V (Ni-CD or Ni-MH) or 1.5V (carbon-zinc or alkaline) battery;
C1 680µF electrolytic capacitor (10V);
C2/3 100nF polyester capacitor (63V);
C4/9 2.2µF electrolytic capacitor (6,3V);
C5/10 47µF electrolytic capacitor (10V);
C6/11 33nF polyester capacitor (63V);
C7/12 47nF polyester capacitor (63V);
C8/13 220µF electrolytic capacitor (10V);
D 1N4001 rectifier diode (D1 in the diagram, mistake again);
FTE1/2 2-1/2 inch speaker (8Ohm, 0.5W);
IC1/2 LM386 audio power amplifier;
R1/6 1,5K carbon resistor (5% tol., 1/8W);
R2 10K double gang potenciometer (10% tol., 1/8W);
R3/7 1,5K carbon resistor (5% tol., 1/8W);
R4/8 15K carbon resistor (5% tol., 1/8W);
R5/9 10Ohm carbon resistor (5% tol., 1/8W);
S1 SPDT switch;
S2 SPST switch.
Notes:
- C1 is only for improving power supply filtering. Its capacitance values is the half of the needed for a filtering with 20% ripple.
- To avoid motorboating, C2 and C3 should be kept close to the respective amplifiers ICs (respectively IC1 and IC2).
- Version 2 has a smaller gain to avoid distortion.
The overall gain of this circuit is 26dB. To compensate poor bass response from the speakers, this circuit has a 6dB "bass boost" (treble attenuation actually, >1KHz).
FTE2 corresponds to the right channel. FTE1 corresponds to the left channel and is installed in a separate box, apart from FTE2 and the circuit. The connection between FTE2 and the amplifier circuit can be made using a standard RCA/RCA plug.
View attachment CSA300mW.pdf
List of components (version 1):
B1-4 - 1.2V (Ni-CD or Ni-MH) or 1.5V (carbon-zinc or alkaline) battery;
C1 680µF electrolytic capacitor (10V) (typo);
C2/3 100nF polyester capacitor (63V);
C4/9 2.2µF electrolytic capacitor (6,3V);
C5/10 47µF electrolytic capacitor (10V);
C6/11 33nF polyester capacitor (63V);
C7/12 47nF polyester capacitor (63V);
C8/13 220µF electrolytic capacitor (10V);
D 1N4001 rectifier diode (D1 in the diagram, my mistake);
FTE1/2 2-1/2 inch speaker (8Ohm, 0.5W);
IC1/2 LM386 audio power amplifier;
R1 10K double gang potenciometer (10% tol., 1/8W);
R2/5 4,7K carbon resistor (5% tol., 1/8W);
R3/6 15K carbon resistor (5% tol., 1/8W);
R4/7 10Ohm carbon resistor (5% tol., 1/8W);
S1 SPDT switch;
S2 SPST switch.
View attachment CSA300mW(2).pdf
List of components (version 2):
B1-4 - 1.2V (Ni-CD or Ni-MH) or 1.5V (carbon-zinc or alkaline) battery;
C1 680µF electrolytic capacitor (10V);
C2/3 100nF polyester capacitor (63V);
C4/9 2.2µF electrolytic capacitor (6,3V);
C5/10 47µF electrolytic capacitor (10V);
C6/11 33nF polyester capacitor (63V);
C7/12 47nF polyester capacitor (63V);
C8/13 220µF electrolytic capacitor (10V);
D 1N4001 rectifier diode (D1 in the diagram, mistake again);
FTE1/2 2-1/2 inch speaker (8Ohm, 0.5W);
IC1/2 LM386 audio power amplifier;
R1/6 1,5K carbon resistor (5% tol., 1/8W);
R2 10K double gang potenciometer (10% tol., 1/8W);
R3/7 1,5K carbon resistor (5% tol., 1/8W);
R4/8 15K carbon resistor (5% tol., 1/8W);
R5/9 10Ohm carbon resistor (5% tol., 1/8W);
S1 SPDT switch;
S2 SPST switch.
Notes:
- C1 is only for improving power supply filtering. Its capacitance values is the half of the needed for a filtering with 20% ripple.
- To avoid motorboating, C2 and C3 should be kept close to the respective amplifiers ICs (respectively IC1 and IC2).
- Version 2 has a smaller gain to avoid distortion.