This circuit is derived from the Portable Headphone Amplifier featuring an NPN/PNP compound pair emitter follower output stage. An improved hasil 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.
Class-A Headphone Amplifier Circuit diagram:
The above 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.
Note:
Before setting quiescent current rotate the volume control P1 to the minimum, Trimmer R6 to zero resistance and Trimmer R3 to about the middle of its travel.
Connect a suitable headphone set or, better, a 33 Ohm 1/2W resistor to the amplifier output.
Connect a Multimeter, set to measure about 10Vdc fsd, across the positive end of C5 and the negative ground.
Switch on the supply and rotate R3 in order to read about 7.7-7.8V on the Multimeter display.
Switch off the supply, disconnect the Multimeter and reconnect it, set to measure at least 200mA fsd, in series to the positive supply of the amplifier.
Switch on the supply and rotate R6 slowly until a reading of about 100mA is displayed.
Check again the voltage at the positive end of C5 and readjust R3 if necessary.
Wait about 15 minutes, watch if the current is varying and readjust if necessary.
P1 : 22K Dual gang Log Potentiometer R1 : 15K R2 : 220K R3 : 100K R4 : 33K R5 : 68K R6 : 50K R7 : 10K R8,R9 : 47K R10,R11 : 2R2 R12 : 4K7 R13 : 4R7 R14 : 1K2 R15,R18 : 330K R16 : 680K R17,R19 : 220K R20,R21 : 22K C1,C2,C3,C4 : 10?F/25V C5,C7 : 220?F/25V C6,C11 : 100nF C8 : 2200?F/25V C9,C12 : 1nF C10 : 470pF C13 : 15nF D1 : LED D2,D3 : 1N4002 Q1,Q2 : BC550C Q3 : BC560C Q4 : BD136 Q5 : BD135 IC1 : 7815 T1 : 15CT/5VA Mains transformer SW1 : 4 poles tiga ways rotary Switch SW2 : SPST slide or toggle Switch
J1_____________RCA audio input socket J2_____________6mm. Or 3mm. Stereo Jack socket PL1____________Male Mains plug
