Class one Headphone Amplifier Circuit diagram. This circuit 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.
Class one Headphone Amplifier Circuit diagram :
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.
Parts List :
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 : 10µF/25V C5,C7 : 220µF/25V C6,C11 : 100nF C8 : 2200µF/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 3 ways rotary Switch SW2 : SPST slide or toggle Switch
