The Soul is a DAC (digital to analog converter), headphone amp and preamp with DSP (digital signal processing). It’s the best preamp I have owned and a unique piece of kit. It has the transparency of a passive attenuator with the flexibility of a DAC and active preamp. This page summarizes the info I have on it.

• Home page at Meier Audio.
• Measurements: frequency response, DA filters, noise, distortion, DSP effects, etc.
• Subjective listening review: links to part 1, the introduction.
• Detailed info on its selectable DA filters.

More specifically, the Soul is an AIO or “all in one” device providing 4 functions:

• Fully balanced analog line-level preamp
• Fully balanced analog heaphone amp
• DAC: Digital Analog Converter
• DSP: Digital Signal Processing with features like tone controls, image crossfeed, and notch filters

So what’s the deal? DACs, headphone amps and preamps have improved a lot over the past 20 years and nowadays SOTA sound quality is commodified. What’s so special about the Soul? Jan Meier incorporates both engineering and psychoacoustics into his designs. Without getting into subjective impressions, here are some its engineering features.

• Stepped gain-volume control
  • The volume knob is a stepped attenuator that sets the analog gain ratio, instead of attenuating a fixed gain ratio. In other words, it swaps the resistors in the gain-feedback loop.
  • Benefit: lower noise & distortion and perfect L-R channel balance, especially at low-medium volume settings
• 100% balanced/differential both D and A
  • The Soul is fully balanced/differential from the DAC chip to the analog outputs.
  • Benefit: lower noise and distortion, no ground loops
• Switching power supplies
  • The Soul has 4 separate power supplies, all switching at about 70 kHz
  • Benefit: lower noise, eliminates 50/60 Hz hum
• Dual WM8741 chips in mono mode
  • The Soul DAC uses a pair WM8741 chips, each in mono mode, one for each channel (instead of using a single WM8741 chip in stereo mode).
  • Benefit: lower noise and distortion
• Maximum oversampling at all rates
  • The Soul sets the WM8741 chip in “OSR high” mode which oversamples all data to the chip’s max rate (44.1k is 8x, 192k is 2x).
  • Benefit: lower noise & distortion, smoother high frequency response
• FF internal feedback pre-emphasis
  • The Soul applies internal pre-emphasis to minimize distortion in the frequency range where human hearing is most sensitive
  • Benefit: pyschoacoustically shaped (perceptually lower) noise & distortion, improved clarity and detail/resolution
• Top quality parts: Neutrik, Alps, Lorlin, AD797 opamps, BUF634, WM8804, Nichicon caps, etc.
  • The Soul uses top quality parts and build quality, made by Lake People in Germany.
  • Benefit: reliability, durability, longevity

The Soul’s analog stages and DSP are state of the art. You cannot get anything better for any price. The Soul’s DAC is very good but not state of the art. The WM8741 is old and has been eclipsed by newer chips. Whether one can hear the difference is a different question. However, the Soul has a switchable loop that enables one to use an external DAC. Thus, it is future-proofed.

The Soul’s maximum output level is 8 V and 600 mA. Eight volts is what you get for a full-scale digital signal with the volume knob maxed, and it has enough current to support that down to about 14 ohm loads. This gives the following max power levels (of course, you can interpolate using V=IR, and P=IV):

In the above you can see that the Soul is not current limited for most headphones; its 600 mA max current capability is enough to support its 8 V max output voltage down to 14 ohms, where it can deliver 4.6 watts of power. For example, consider the HifiMan HE-6 (one of the least efficient, most power-hungry headphones). The Soul can deliver 8 V, 160 mA and 1.28 W of power to this headphone. The HE-6 voltage sensitivity is 1.25 V for 94 dB, so 8 V is 16 dB louder, which gives 94 + 16 = 110 dB.