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Sonoma Model One: A revolutionary electrostatic headphone system

By Kenny Yeo - 16 May 2017

The Sonoma Model One headphone system - Part 2

The Sonoma Model One Energizer/DAC

The Sonoma Model One headphones come with its special energizer because of its unique energy requirements.

Now let’s talk about the energizer and DAC combo. Because the headphones use Warwick Audio’s patented HPEL transducer, it requires a special energizer from Sonoma Acoustics and cannot be mixed and matched with third-party energizers. Mainly, the issue lies with the Sonoma Model One’s need for a very high 1350V DC bias voltage, which I believe is a consequence of its single stator design. Most other electrostatic headphones only require about 500V to 600V.

The energizer and DAC combo unit is made out of a solid billet of aluminum, weighs about 2.5kg, and looks handsome and minimalistic. It does take up quite a bit of desk space, but that’s par for the course when it comes to high-end desktop amplifier and DAC combos. On the front panel, there’s a chunky flip switch that lets users choose between analog and digital inputs, a large volume control knob, and the headphone outputs.

The energizer features USB and digital coaxial inputs, and also analog inputs via RCA and a 3.5mm audio jack.

Round the back, there’s two digital inputs in the form of USB and digital coaxial and two analog inputs in the form of your standard RCA jacks and a single 3.5mm audio jack. The power switch is located on the far end and there’s another switch that selects between the two analog inputs. There are no RCA outputs so you cannot use this as a standalone DAC or as pre-out to your powered speakers or your speaker amplifier.

The energizer uses a discrete single-ended Class-A design. Audiophiles typically prefer Class-A amplifier design because of their simpler design and inherent lack of distortion, since the output device is always conducting and drawing current at all times throughout the full 360-degree cycle of the waveform. This also means that the output stage is always active, regardless of whether there is a signal or not, which in turn means that the energizer gets fairly hot during operation.

Vents above help keep the energizer cool because of its Class-A output design. The special wave patterns are similar to the ones found on the ear cups.

The energizer also features an integrated digital-to-analog converter (DAC) that accepts digital inputs via USB or digital coaxial. It uses two ESS Sabre Reference DAC chips (one for each channel) that support PCM up to 32-bit and 384kHz as well as DSD up to DSD 128 (5.6MHz) via USB, and PCM up to 24-bit and 192kHz via digital coaxial.

So far so good, all pretty standard stuff for any high-end energizer/amplifier and DAC combo. But this is where things start getting interesting because the energizer and DAC unit also features a 32-bit/384kHz AKM analog-to-digital converter (ADC), which digitizes analog signals coming in from either the RCA analog input or 3.5mm analog input. Why the need for this? That’s because the Sonoma Model One also features a custom-designed 64-bit double precision fixed-point arithmetic digital signal processing running on a multi-core XMOS processor.

The Sonoma Model One relies on a multi-core XMOS processor for its DSP to attain its target frequency response. (Image source: Sonoma Acoustics)

The general consensus, at least amongst diehard audiophiles and purists, is that digital signal processing ruins the purity of the recording and is therefore frowned upon. However, Sonoma Acoustics say that digital signal processing is crucial to achieving their target frequency response of the headphones. 

Unlike most high-end energizers and amplifiers which use an analog potentiometer to control the volume, the Sonoma Model One uses a completely digital volume control system.

In addition, because audio signals are now digitally processed, they were able to also implement a fully digital volume control system, which, Sonoma says, outperforms all pure analog implementations they tested. According to Sonoma, some advantages of this fully digital volume control system include no loss in fidelity and dynamic range, perfect left and right channel matching, no potentiometer irregularities, and no noise issues.

True enough, the volume control knob works well. Some amplifiers I have tried have exhibited channel imbalances at low volume levels, but not the Sonoma Model One.

In any case, it is the use of a DSP that makes the Sonoma Model One unique in the world of high-end audio. Where most high-end audio systems place great emphasis on analog purity, the Sonoma Model One is unashamedly digital in its approach to good sound. But does it succeed? I put on some music to find out and detailed my findings over the next page.

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9.0
  • Design 8.5
  • Performance 9
  • Features 8.5
  • Value 8.5
The Good
Highly detailed and textured sound
Incredible soundstage
Great build quality
Advanced DSP
Comes with energizer and DAC combo
Extensive PCM and DSD music support
The Bad
Excessive clamping force
Energizer runs hot
Energizer has no outputs
Can sound harsh on EDM tracks
Cannot be paired with third-party energizers
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