The Cheapest and Simplest Audiophile Headphone Amp

This small amplifier finds its use not only with headphones for listening to your favorite tunes in good quality or for playing the electric guitar without causing any annoyance to your close ones.

It can also amplify line-level audio if any of your audio system components have too low sensitivity or output levels.

Our amplifier also has a low output impedance and a reasonably high input impedance—50 kilo-ohms. So, the amplifier serves dual purposes as a buffer with gain and as a power amplifier for headphones.

The design is inexpensive and quite compact, so it can be used in almost any project. The bipolar power supply is not required; any stabilized power source or 12 to 18-volt battery is sufficient.

This amplifier has a linear stereo input, not a Hi-Z instrumental input, for connecting an electric guitar. Therefore, if you play the guitar, you will need an additional preamp.

Headphone amplifiers are assembled using transistors, tubes, and microchips. The tubes add a pleasant warmth to the sound by adding even harmonics to the signal. We have already looked into this in a post on the DIY tube amplifier.

That sweet little amplifier is an excellent buffer for a hi-fi audio system. It can happily work with an electric guitar. But its output power is not enough for headphones. (Yet it can be an excellent preamp for our headphone amp today.) A tube amplifier needs to be powered with an AC transformer, which is not a portable solution.

Discrete transistor amplifiers can be decent, but they contain many elements. They need to be carefully configured, pairs of transistors with the same parameters must be picked, and a large quantity of high-quality capacitors must be used.

Some audiophiles say the best sound is created only with special carbon-fiber resistors. If the influence of the design and materials of capacitors on the quality of sound reproduction is objectively proven and has been measured, valuable parameters for resistors, from a technical standpoint, are accuracy and temperature stability. Metal film resistors are primary candidates, as they are known for this feature.

If you didn't already know, low-power carbon resistors are usually beige (modern film) and brown (vintage composite), and metal film resistors are often blue. But there are many exceptions.

Be that as it may, music is for pleasure. Music is an art, and this applies not only to composing and performing but also to playing back, listening, and making musical instruments and equipment. Therefore, subjective opinions and feelings must be respected because music is just about them. And the components should fit the person who creates the amplifier and the person who will listen to it.

Any way you approach it, creating transistor and tube amplifiers costs money and time, takes up space, requires skills, and sometimes requires special equipment for adjustment. Integrated circuits make everything much more compact, accessible, and simpler.

And if we talk chips for audio processing, first, we need to discuss operational amplifiers.

By the way, LM386 is an op-amp, too, designed to work with a loudspeaker or a headphone. I'm sure you've already used LM386 on your devices. Clearly, it is not at all an amplifier for high-quality sound reproduction through headphones or a small speaker.

Although, oddly enough, with a large 12-inch guitar speaker (not the 80-watt Celestion Seventy 80, better something like a 25-watt Greenback), the LM386 can sound very good in the room, it has just enough volume to be used as a bedroom amplifier.

But guitar amplification is a totally separate thing. You need to amplify specific guitar frequencies; the LM386 can handle this fine. And when you need to reproduce with high fidelity the sound of an entire orchestra, a rock band, or birds chirping in the forest, you'll need something bigger.

So, we will use NE5532.

The best op amp for audio

"There is probably no music on the planet that has not passed through a hundred or more 5532s on its way to the consumer."
Douglas Self, British electronics engineer

Please do not confuse NE5532 for NE532. The NE532 is just a complete analog of the good old LM358, developed in 1972 as an industry standard for operational amplifiers.

Surprisingly, the LM358 circuitry is built into many other integrated circuits. For example, the TL494 PWM controller contains two error amplifiers constructed according to the LM358 diagram.

We often use the LM358, sometimes even for audio processing, but in most cases, we still prefer the TL072 and NE5532. Why is that? This is precisely what we will talk about today.

NE5532 are considered operational amplifiers for enthusiasts, and rightfully so, one can find them in even the most expensive and prestigious audio equipment. From 1979 to 2007, that is, for 28 years, NE5532 was unattainable—the best in class! And then LM4562 came along.

There are several more expensive and more advanced operational amplifiers for audio, including those assembled on a printed circuit board from discrete components rather than an integrated chip design. After all, progress never stops, and there is no limit to perfection.

In fact, in the vast majority of cases, the characteristics of the NE5532 are more than sufficient for high-quality audio signal processing. This is confirmed by its application in various professional music and sound recording equipment and household high-fidelity audio systems.

This is all thanks to the fact that the NE5532 has very low noise, extremely low harmonic distortion (THD) with an appropriate switching circuit, and, very significantly, a high slew rate. It is equal to 9 V/uS versus 0.3 9 V/uS for the LM358.

It would seem that even LM358 has a gain bandwidth of 1 MHz (according to datasheets from different manufacturers, from 700 to 1200 kHz). However, gain bandwidth does not mean the effective gain band but just the frequency at which the unity gain is preserved.

When the voltage is amplified by +20 decibels, i.e., 10 times, the LM358's gain begins to decline already at a 10 kHz frequency. In contrast, for the NE5532, this frequency is 200 kHz.

Why does an audio signal need wide bandwidth anyway? An average human cannot hear sounds with a pitch above 20 kHz. Besides frequency, the attack of sound matters. The wave's shape matters, too, and to avoid distorting it, you need a bandwidth 10 times wider.

So, our amplifier is called "47" and consists of two identical channels - left and right. Each channel is built on a dual NE5532 operational amplifier. Resistors R1 and R2 divide the supply voltage in half, forming a common virtual ground for both channels.

Op-amp U1A is used in a non-inverting configuration: the input signal is applied to the non-inverting input, and resistors in the feedback loop set the gain from the output to the inverting input.

In our case, the coefficient equals (4.7 + 10) / 4.7 = 3.13, 9.9 dB.

Operational amplifier U1B is connected as a repeater with unity gain and simply doubles the channel output current. Resistors R8 and R9 limit the current to protect the headphones and amplifier.

The second channel is assembled according to the same diagram as the first one on a separate U2 chip. If you don't need a second channel, you can build just one using one chip.

This amp sounds very clean. Unlike guitar equipment, it does not alter the sound but simply reproduces the input signal with high quality.

So, high fidelity is not always difficult and expensive. Sometimes, you can achieve excellent results simply by finding a suitable scheme.