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6V battery operated Class-B circuitry with low distortion. Some fans of high-fidelity headphones would rather employ battery-operated headphone amplifiers for "table" applications at home as well as portable devices. Their needs are the focus of its design. Making this a push-pull Class-B setup improves the output driving capabilities. With low standing and mean current consumption, output power can reach 100mW RMS into a 16 Ohm load at 6V supply, enabling extended battery life.
Resistors:
P1 = 22K Potentiometer
R1 = 15K Resistor
R2 = 100K Resistor
R3 = 100K Resistor
R4 = 47K Resistor
R5 = 470R Resistor
R6 = 500R Resistor
R7 = 1K Resistor
R8 = 18K Resistor
R9 = 18K Resistor
R10 = 2.2R Resistor
R11 = 2.2R Resistor
R12 = 33R Resistor
R13 = 4.7K Resistor
Capacitors:
C1 = 10uF-25V Capacitors
C2 = 10uF-25V Capacitors
C3 = 100nF-63V (PF)
C4 = 220uF-25V Capacitors
C5 = 100nF-63V (PF)
C6 = 220uF-25V Capacitors
Semiconductors:
Q1 = BC560C PNP Transistor
Q2 = BC560C PNP Transistor
Q3 = BC550C NPN Transistor
Q4 = BC550C NPN Transistor
Q5 = BC560C PNP Transistor
Q6 = BC327 PNP Transistor
Q7 = BC337 NPN Transistor
Miscellaneous:
J1 = RCA Audio Input Socket
J2 = 3mm Stereo Jack Socket
B1 = 6V Battery Rechargeable
SW1=SPST Slide or Toggle Switch
Notes:
- All components (apart from P1, SW1, J2, and B1) must be doubled for the circuit to be used in stereo.
- Turn the volume control P1 to the lowest setting, the trimmer R6 to the greatest resistance, and the trimmer R3 to around the midpoint of its travel before establishing the quiescent current.
- A 33 Ohm 1/2W resistor is a better option than headphones when connecting to the amplifier's output.
- Turn on the power and use a multimeter set to roughly 10Vdc fsd to measure the battery voltage.
- Attach the multimeter between the negative ground and the positive end of C4.
- To read precisely half of the previously measured battery voltage on the multimeter display, rotate R3.
- Turn off the power, disconnect the multimeter, and reconnect it in series with the amplifier's positive supply, calibrated to measure around 10mA fsd.
- Turn on the supply and slowly turn R6 until a reading of roughly 3mA appears on the screen.
- Recheck the voltage at C4's positive end and, if required, adjust R3.
- After around 15 minutes, check to see if the current is changing, and make any required adjustments.
- The amplifier can be driven to its maximum output power and R3 adjusted to get a symmetrical clipping of the sine wave displayed by those fortunate enough to have access to an oscilloscope and a 1KHz sine wave generator.
- 100mW RMS at 16 ohms
- 60mW RMS at 32 ohms
- 35mW RMS at 64 ohms
- 22.5 mW RMS at 100 ohm
- 8.5mW RMS at 300 ohms
Sensitivity: 32 Ohm load (31 mW) at 160 mV input with a 1 v RMS output.
200mV input onto a 32-ohm load (50mW) yields a 1.27V RMS output.
At 1V RMS, the frequency response is flat between 45Hz and 20 KHz, -1dB at 35Hz, and -2dB at 24Hz.
Total harmonic distortion at 1 KHz into a 16-ohm load:
RMS voltage of 1V (62mW) 0.015 percent 1.27V RMS (100mW, clipping start) 0.04%
1V RMS (62mW) is the total harmonic distortion into a 16-ohm load at 10 KHz. 0.05 percent 1.27V RMS (100mW, clipping start) 0.1%
Indestructibly steady under capacitive loads