Portable 9v Headphone Amplifier

High Quality One-IC unit, Low current consumption. After several requests by correspondents, the decision of designing a 9V powered Headphone Amplifier was finally taken. The main requirement was to power the circuit by means of a common, PP3 (transistor radio) alkaline battery. So, implementing a low current drawing circuit was absolutely necessary, though preserving a High Quality performance.

Portable 9v Headphone Amplifier Circuit Diagram:

Amplifier Circuit Diagram


Parts:
P1 = 22K
R1 = 18K
R2 = 68K
R3 = 68K
R4 = 68K
R5 = 18K
R6 = 68K
C1 = 4.7uF-25v
C2 = 4.7uF-25v
C3 = 22pF
C4 = 220uF-25v
C5 = 220uF-25v
C6 = 4.7uF-25v
C7 = 22pF
C8 = 220uF-25v
J1 = 3.5mm Stereo Jack
B1 = 9V Alkaline Battery
IC1 = NE5532-34
SW1 = SPST Toggle Switch

The appearance of the 5534 low-noise op-amp at a reasonable price was much appreciated by audio designers. It is now difficult or impossible to design a discrete stage that has the performance of the 5534 without quite unacceptable complexity. 5534 op-amps are now available from several sources, in a conventional 8-pin d.i.l. format. This version is internally compensated for gains of three or more, but requires a small external capacitor (5-15pF) for unity-gain stability. The 5532 is a very convenient package of two 5534s in one 8-pin device with internal unity-gain compensation, as there are no spare pins.

The 5534/2 is a low-distortion, low-noise device, having also the ability to drive low-impedance loads to a full voltage swing while maintaining low distortion. Furthermore, it is fully output short-circuit proof. Therefore, this circuit was implemented with a single 5532 chip forming a pair of stereo, inverting amplifiers, having an ac gain of about 3.5 and capable of delivering up to 3.6V peak-to-peak into a 32 Ohm load (corresponding to 50mW RMS) at less than 0.025% total harmonic distortion (1kHz & 10kHz). If we consider that the mean current drawing at a power output of 15mW per channel is around 12-13mA (both channels driven), this Headphone Amplifier will become a 'must' for many DIY enthusiasts needing a High Quality, High Performance portable device.

Technical data
Sensitivity:
    200mV RMS for 15.6mW RMS output
    350mV RMS for 50mW RMS output
Maximum undistorted output: 3.6V Peak-to-peak
Frequency response: flat from 40Hz to 20KHz; -2.3dB @ 20Hz
Total harmonic distortion @ 1KHz: <0.025% at all power outputs up to 50mW RMS
Total harmonic distortion @10KHz: <0.02% at all power outputs up to 50mW RMS
Total current drawing @ 9V supply (both channels driven):
    Standing current: 8.5mA
    Mean current drawing @ 15mW RMS per channel: 12mA
    Mean current drawing @ 35mW RMS per channel: 17mA

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