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 ES9219C. 


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


User-selectable amp gain mode

  • Normal 1V RMS
  • High 2V RMS
  • Both provide the same sound performance.
  • They could sound a little different from each other. But, it doesn't mean that which one is better.

Normal 1V RMS mode

  • Recommended for the most IEMs
  • Longer battery time and the lower noise floor

High 2V RMS mode

  • +6dB higher maximum output level
  • Recommended for headphones

*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.


Auto Volume Correction

  • The firmware adjusts the volume and keeps the current output level when switching the gain mode.
  • You will experience no difference in loudness when switching the mode to 2VRMS. But you will have the max volume extended by +6dB.


In addition to the output power mode option, Qudelix's proprietary software drives ES9219C DAC/AMP in two different ways, to trade off the battery time and Sound Quality.

  • Standard Profile (ECO mode)
    • Standard DAC Operating Clock
    • Standard Output Bias Current
    • Best Efficiency with good enough sound quality
    • The best trade-off for battery time and sound quality
    • Good for mobile and outdoor use cases
  • Performance Profile (SPORT mode)
    • Highest DAC Operating Clock
    • High Output Bias Current
    • Best Performance
    • Best Sound Quality with lesser battery time
  • USB powering to the device overrides the current profile and switches it to PERFORMANCE mode temporarily.

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 ES9219C, while the 3.5mm unbalanced works with single DAC. 

*ESS discontinued ES9218. From Nov 2021, 5K DAC/AMP is manufactured with ES9219C, which is pin-to-pin compatible with ES9218P.



Florin Andrei

The Distortion Compensation option is still not explained. What does it do?

Mau Lopez

Great post. Very clear explanation. I think this explanation is way better than the one in the iOS app. I hope you consider updating the explanation in the app. Regards

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