Learning Electronics

Learning Electronics

Learn to build electronic circuits

Pure Class-A Headphone Amplifier Schematic

400mW RMS into 32 Ohm load, Single-rail Supply - Optional Tilt Control

This design is derived from the Portable Headphone Amplifier featuring an NPN/PNP compound pair emitter follower output stage. An improved output driving capability is gained by making this a push-pull Class-A arrangement. Output power can reach 427mW RMS into a 32 Ohm load at a fixed standing current of 100mA. The single voltage gain stage allows the easy implementation of a shunt-feedback circuitry giving excellent frequency stability.

Tilt control:

The mentioned shunt-feedback configuration also allows the easy addition of frequency dependent networks in order to obtain an useful, unobtrusive, switchable Tilt control (optional). When SW1 is set in the first position a gentle, shelving bass lift and treble cut is obtained. The central position of SW1 allows a flat frequency response, whereas the third position of this switch enables a shelving treble lift and bass cut.

Circuit diagram:
  Pure Class-A headphone Amplifier Circuit Schematic Diagram
Class-A Headphone Amplifier Circuit Diagram


P1 = 22K Dual gang Log Potentiometer (ready for Stereo)

R1 = 15K 1/4W Resistor
R2 = 220K 1/4W Resistor
R3 = 100K 1/2W Trimmer Cermet
R4 = 33K 1/4W Resistor
R5 = 68K 1/4W Resistor
R6 = 50K 1/2W Trimmer Cermet
R7 = 10K 1/4W Resistor
R8 = 47K 1/4W Resistors
R9 = 47K 1/4W Resistors
R10 = 2R2 1/4W Resistors
R11 = 2R2 1/4W Resistors
R12 = 4K7 1/4W Resistor
R13 = 4R7 1/2W Resistor
R14 = 1K2 1/4W Resistor
R15 = 330K 1/4W Resistors (Optional)
R16 = 680K 1/4W Resistor (Optional)
R17 = 220K 1/4W Resistors (Optional)
R18 = 330K 1/4W Resistors (Optional)
R19 = 220K 1/4W Resistors (Optional)
R20 = 22K 1/4W Resistors (Optional)
R21 = 22K 1/4W Resistors (Optional)

C1 = 10µF 25V Electrolytic Capacitors
C2 = 10µF 25V Electrolytic Capacitors
C3 = 10µF 25V Electrolytic Capacitors
C4 = 10µF 25V Electrolytic Capacitors
C5 = 220µF 25V Electrolytic Capacitors
C6 = 100nF 63V Polyester Capacitors
C7 = 220µF 25V Electrolytic Capacitors
C8 = 2200µF 25V Electrolytic Capacitor
C9 = 1nF 63V Polyester Capacitors (Optional)
C10 = 470pF 63V Polystyrene or Ceramic Capacitor (Optional)
C13 = 15nF 63V Polyester Capacitor (Optional)
C11 = 1nF 63V Polyester Capacitors (Optional)
C12 = 1nF 63V Polyester Capacitors (Optional)

D1 = 5mm. or 3mm. LED
D2 = 1N4002 100V 1A Diodes
D3 = 1N4002 100V 1A Diodes

Q1 = BC550C 45V 100mA Low noise High gain NPN Transistors
Q2 = BC550C 45V 100mA Low noise High gain NPN Transistors
Q3 = BC560C 45V 100mA Low noise High gain PNP Transistor
Q4 = BD136 45V 1.5A PNP Transistor
Q5 = BD135 45V 1.5A NPN Transistor

IC1 = 7815 15V 1A Positive voltage regulator IC
T1 = 220V Primary, 15+15V Secondary-5VA Mains transformer

SW1 = 4 poles 3 ways rotary Switch (ready for Stereo)
SW2 = SPST slide or toggle Switch

J1 = RCA audio input socket
J2 = 6mm. or 3mm. Stereo Jack socket
PL1 = Male Mains plug


Technical data: