Stereo headphone amplifier
Posted on Dec 25, 2012 3177
Under: Audio Amplifier Circuits
The ping of the cymbals, crack of the snare drum, thonk of the bass - none of these comes through on my low-budget speakers. Sometimes they sound so fuzzy I want to hide behind the couch until it’s over. But headphones...ah, heaven! There are probably as many headphone amp designs as there are headphones, but all aren’t created equal. The cheesy headphone-amp circuits in most stereo gear aren’t up to the standards of the main amp components, and many CD players and cassette decks don’t even have them. This do-it-yourself stereo headphone amp sounds clean and clear, and uses just two, inexpensive chips. It’s great for practice, multitrack monitoring, or just plain listening as a receiver/integrated-amp substitute.
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he circuit gets its zip from two National Semiconductor LM386 Low Voltage Audio Power Amp ICs, one for each side of the stereo path. The left and right channels are identical. Refer to the schematic, Fig. 1, using the left channel as a guide. Dual potentiometer R1A serves as variable input-attenuator (the dual pot controls both channels); R2 isolates C2, which capacitively couples the input. Cl bypasses high-frequency input noise to ground; C3 bypasses the inverting input. R3 and C4 bypass the power supply. R6 and C7 bypass the output; C8 capacitively couples it. The LM386 is internally configured to provide a gain of 26 dB: this is a bit too much for line-level inputs. R4 reduces the gain by -6 dB. If you want to tailor the response for guitar signal input, you will have to add some additional components (indicated with dotted lines), because the guitar output is a low-voltage signal with a predominance of high frequencies. C5 (which substitutes for the indicated jumper) rolls off the high frequencies at -6 dB/octave, with a cutoff frequency of about 5kHz. R5 and C6 provide about +6dB of gain recovery to boost the signal. The sound quality you’ll get from your headphone amp will be directly proportional to the quality of the passive components it incorporates. Use the best poly and low-leakage electrolytic capacitors you can obtain. Metal-film resistors help maximize the signal-to-noise ratio, though I’ve had good results...