We want the device to work as a universal DAC/AMP for both high-sensitivity IEMs as well as high-impedance open-back headphones. We want it simple, small, yet but powerful. In addition to the sound quality and the maximum output power, we also need to consider the battery time as well, concerning the nature of the device.

We've tried many DACs and Amplifier ICs and found ESS9218p is the best option for our goal. Besides the sound quality, the primary advantage of ESS9218p is that the built-in amplifier delivers the maximum output voltage up to 2V RMS. Furthermore, it supports the 1V RMS option at the same sound quality to save power consumption.

For high-sensitivity IEMs, the amplifier noise figure is the most important. The high-sensitivity IEM is so sensitive that it translates every electrical noise or thermal drift into audible acoustic sound, usually white noise.

On the other hands, the high-impedance headphones require a higher power amplifier. Those headphones usually have low sensitivity, and they are free from the white noise affected by the amplifier noise characteristics. Instead, they need higher power from the amplifier output to deliver enough loudness and headroom.

We designed the software and the app to provide full access to every internal option of ES9218p. 

3.5mm Unbalanced (Single Ended)

1VRMS Mode

For the most IEMs, The 2V RMS output would be too much. The 1V RMS mode offers the best power efficiency at the same sound quality as the 2V RMS mode.

2VRMS Mode

For low sensitivity IEMs or headphones, the 2V RMS mode delivers enough headroom and loudness.

2.5mm Balanced (Full Differential)

2VRMS Mode

The full differential direct audio path delivers the best linearity and separation, still with enough battery time.

4VRMS Mode

The maximum output power


2V RMS mode vs. 1V RMS mode

  • Both modes provide the same sound performance.
  • 2V RMS mode provides a +6dB greater output level at a little higher background noise floor.
  • Both modes could sound a little different from each other. But, it doesn't mean that which one is better.
  • In most cases, it is highly recommended using the 1V RMS mode, which provides longer battery time and the lower noise floor.


Best Practice:

For high sensitivity IEM, the 1V RMS mode offers the best noise performance and power efficiency. There's no reason to keep the low gear on the highway.


In addition to the output power mode option, 5K provides two different operating profiles, to trade off the battery time and Sound Quality, 

  • Standard Profile:
    • Standard DAC Operating Clock
    • Standard Output Bias Current
  • Performance Profile:
    • Highest DAC Operating Clock
    • High Output Bias Current
  • The performance profile provides the best sound quality.
  • For the mobile and outdoor use cases, the standard profile provides the best power efficiency and good enough sound quality, by trading off 2~3dB degradation in sound performance.


The operating profile automatically switched to the performance mode upon the presence of any USB VBUS connection. 

NOTE: The 2.5mm Balanced mode fully uses two ES9218p, while the 3.5mm unbalanced works with single DAC.