The Soul is a DAC, headphone amp and preamp. It’s the best preamp I have owned and a unique piece of kit. It has the transparency of a passive attenuator and the flexibility of a DAC and active preamp. This page summarizes the info I have on it.
- Home page at Meier Audio.
- Review: links to part 1, the introduction.
- Measurements: frequency response, DA filters, noise, distortion, DSP effects, etc.
- Detailed info on its selectable DA 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 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.
- Dual WM8741 chips in mono mode
- The Soul 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
- Switching power supplies
- The Soul has 4 separate power supplies, all switching at about 70 kHz
- Benefit: lower noise and distortion, eliminates 50/60 Hz hum
- 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.
- FF internal feedback pre-emphasis
- The Soul applies internal pre-emphasis to minimize noise & distortion in the frequency range where human hearing is most sensitive
- Benefit: pyschoacoustically shaped (perceptually lower) noise & distortion
- 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 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):
|R (load)||V||I (mA)||P (mW)|
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. This is enough power to drive even the HifiMan HE-6 (one of the least efficient, most power-hungry headphones) to about 110 dB SPL.