Can someone shed some light on the difference between a pure “line out” and relatively low-powered headphone amp.

For example (to cite a use-case): I still love my trusty Fiio A3 which (to my ears) sounds great as a small, standalone portable headphone amp. Let’s say I want to listen through my iPhone and I plug the standard Apple DAC - 3.5mm dongle into my phone (which by most accounts is an excellent DAC/AMP), but the Apple dongle isn’t powerful enough to power the headphones I’m using, so I output the Apple dongle to the A3 (and then plug headphones into A3).

The Apple dongle is (to my understanding) a DAC/AMP (that can power many IEMs really nicely). So am I double amping here? Am I going to damage the amp by running a non-Line out single into it? And will the sound quality be degraded (compared to a device that can output a “line out” to the amp)?

  • FromWitchSide@alien.topBEnglish
    1·
    11 months ago

    As mentioned headphone amps usually are designed for 2V signal. If the voltage is too high then the amplifier input will clip (distort), unlikely to be the case for Apple dongle since its 0.5-1V. If the voltage is lower then the output from the amplifier will be lower as well as the gain is a ratio (Av for voltage).

    So when you are stacking amplifiers then you are facing an issue of matching output of preceding one with input of the following one.

    Another reason why using multiple amplifiers is not advisable is because every gain stage adds its own noise, and more importantly harmonic distortion. This is actually a trick used by some electric guitar players to get a highly saturated driven sound from a solid state devices :P However this is hardly an issue given how low noise and distortion is from modern headphone amps.

    Also all of that is kind of relative, since DAC chips can output 2V, and dongles like Apple usually output straight from the DAC chip, similarly to how the same chips would output to Line Out in a desktop DAC. To begin with a chip is an integrated circuit, which is made of parts like transistors and contains some amplification. So the idea is more like “do not stack too many of gain stages, especially powerful ones” than “never connect headphone out to the amplifier”.