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10-29-2026, 04:08 PM
Hi Guys
A dedicated headphone amplifier should have one feature that a standard power amp driving room speakers does not need: a mixer.
The mixer is actually a stereo cross-feed bringing a bit of the right-channel sound into the left side, and the same amount of left-channel sound into the right. This blending achieves a sound similar to what we hear when listening to speakers in a room. In the room situation, each ear hears sounds from both speakers and we can localise instrument and voice sounds that were mixed more-left and more-right and right down the middle.
Using standard headphones and the common style of headphone amplifier, the sonic location of instruments will reflect the true mix designed by the recording engineer, and it will not be too musical unless the engineer mixed using headphones only. In most cases, small room speakers are used to monitor the mix through and the mix is inherently optimised for playback through room speakers.
In the cross-feed headphone amp, one can preset the cross-feed level or have it be variable. One can also decide whether the cross-feed signals are full-bandwidth or slightly "dulled" using a low-pass filter. The latter could be made adjustable, as well. The cross-feed could be switchable giving us the opportunity to hear the hard mix or the compensated "room mix". None of this circuitry takes much space and it is all considered to be low-level.
Solid-state headphone amps are typically just opamp ICs. There may be one per channel, which is functional and not excessively high-fidelity. Opamps can be paralleled for more output and until you get to seemingly outrageous numbers, the fidelity still leaves something to be desired. Also, with any of these options so far, we are limited to opamp supply rails which may not give the best headroom for high-impedance 600R headphones.
So, the next step after using a single opamp per channel is usually to add a discreet buffer within the feedback loop. This is typically a complementary pair of transistors. Pretty good fidelity can be achieved this way and the discreet stage can operate from higher supply voltages.
Opamps have improved remarkably since the 1980s and there are now some very good headphone amplifiers based solely on IC opamps. One factor in the popularity of using ICs is that the waste power is distributed and no heat sinks are required, easing the mechanics of the assembly. Many of the best opamps are only available as surface-mount devices. SM devices need large copper areas on the PCB to dissipate their heat, so sometimes this factor cancels the choice of using a tiny SM device over a much larger through-hole device.
Of course, discreet circuitry allows complete freedom of power supply voltages and topology. Going too simple always results in excessive THD, but the wrong direction of modest complexity can do so, as well. In any case, unmeasurable THD is possible via both the discreet and integrated approaches.
If we incorporate tube circuitry into the headphone amplifier, it will have reduced accuracy but may be pleasant to use.
A dedicated headphone amplifier should have one feature that a standard power amp driving room speakers does not need: a mixer.
The mixer is actually a stereo cross-feed bringing a bit of the right-channel sound into the left side, and the same amount of left-channel sound into the right. This blending achieves a sound similar to what we hear when listening to speakers in a room. In the room situation, each ear hears sounds from both speakers and we can localise instrument and voice sounds that were mixed more-left and more-right and right down the middle.
Using standard headphones and the common style of headphone amplifier, the sonic location of instruments will reflect the true mix designed by the recording engineer, and it will not be too musical unless the engineer mixed using headphones only. In most cases, small room speakers are used to monitor the mix through and the mix is inherently optimised for playback through room speakers.
In the cross-feed headphone amp, one can preset the cross-feed level or have it be variable. One can also decide whether the cross-feed signals are full-bandwidth or slightly "dulled" using a low-pass filter. The latter could be made adjustable, as well. The cross-feed could be switchable giving us the opportunity to hear the hard mix or the compensated "room mix". None of this circuitry takes much space and it is all considered to be low-level.
Solid-state headphone amps are typically just opamp ICs. There may be one per channel, which is functional and not excessively high-fidelity. Opamps can be paralleled for more output and until you get to seemingly outrageous numbers, the fidelity still leaves something to be desired. Also, with any of these options so far, we are limited to opamp supply rails which may not give the best headroom for high-impedance 600R headphones.
So, the next step after using a single opamp per channel is usually to add a discreet buffer within the feedback loop. This is typically a complementary pair of transistors. Pretty good fidelity can be achieved this way and the discreet stage can operate from higher supply voltages.
Opamps have improved remarkably since the 1980s and there are now some very good headphone amplifiers based solely on IC opamps. One factor in the popularity of using ICs is that the waste power is distributed and no heat sinks are required, easing the mechanics of the assembly. Many of the best opamps are only available as surface-mount devices. SM devices need large copper areas on the PCB to dissipate their heat, so sometimes this factor cancels the choice of using a tiny SM device over a much larger through-hole device.
Of course, discreet circuitry allows complete freedom of power supply voltages and topology. Going too simple always results in excessive THD, but the wrong direction of modest complexity can do so, as well. In any case, unmeasurable THD is possible via both the discreet and integrated approaches.
If we incorporate tube circuitry into the headphone amplifier, it will have reduced accuracy but may be pleasant to use.
