“I have the simplest tastes. I am always satisfied with the best.”Oscar Wilde

During development of the Sonoma Model One (M1) electrostatic headphone system, particular attention was paid to every aspect of the design to ensure that the system, as a whole, met two critical criteria: to deliver High-Resolution Audio in unparalleled sound quality and to provide the ultimate in listener comfort.

Warwick Acoustics has brought together some of the world’s leading professional audio engineers to create the Sonoma Model One (M1). An integrated headphone system (DAC, amplifier/energizer and open-backed headphone unit), the Sonoma M1 has been optimised from the ground up with one single minded goal. To deliver uncompromising, astonishing HiRes AudioTM performance in a truly exclusive package.

An unparalleled listening experience of unrivalled transparency and tonality that will breathe fresh life into your music.

From the pioneers of high-resolution audio (Hi-Res Audio).

Discover the multi-award winning Sonoma Model One (M1) electrostatic headphone system.


Designed for comfort and optimised for today’s Hi-Res Audio formats, The Sonoma headphone unit employs the finest materials and the latest transducer technology to deliver outstanding acoustic performance.

HPEL Transducers

The patented High-Precision Electrostatic Laminate (HPEL) audio transducer ushers in a new paradigm in the field of electrostatic drivers, and the Sonoma M1 is the first headphone system in the world to use it.

Unlike a traditional electrostatic panel, the sound you hear from a HPEL does not pass through a grid! To take full advantage of this feature, everything has been done in the design of the M1 to keep the areas in front of and behind the transducer as clear as possible so as not to impede the sound waves. Each cell is acoustically independent, but driven in parallel. Thanks to a proprietary Finite-Element Analysis software package, Warwick Acoustics is able to fine tune the characteristics of the ‘drum-skins’ such that they have different resonant frequencies.

The HPEL ensures an extended frequency response, with the panel remaining linear to over 60 kHz. and delivers unprecedented consistency and matching between transducers (< ±0.8 dB difference between left and right channels).

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Injected magnesium earcups

The ear-cups of the M1 are made from Magnesium, the ideal material in which to house the HPEL transducer to ensure optimum performance.

Formed by precision injection moulding at very high pressure. The result is a weight of 10.7 ounces (303 grams) which contributes to outstanding headphone comfort (compared to Aluminium, Magnesium is about ⅓ lighter). Combining excellent strength-to-weight ratio, high stiffness and outstanding EMI/RFI shielding.

Handmade carbretta sheepskin ear-pads

To ensure maximum listening pleasure, comfort in a headphone is of paramount importance.

The pads on the M1 are all handmade from top-grain Cabretta sheepskin leather. Cabretta leather is renowned for its light weight, smoothness, suppleness, and durability. The hides are then tanned by Pittards in the UK, who have been tanning leathers since 1826.

The headband contains stainless steel parts which have a vapour-deposited titanium coating to ensure strength and smooth operation. Made from Nylon 12, it combines sufficient flexibility to adjust to different head sizes, in addition acts to dampen noise and vibration.

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Custom low-capacitance cable

In collaboration with Straight Wire Inc., a totally new, ground-up design was done for the M1. The goal was to meet the following criteria:

– Capacitance is a low 50 pF/m.

– Minimum mechanical noise pick up.

– Maximized signal purity.

The cable, thin, flexible and light is composed of very fine strands of silver-plated oxygen-free high conductivity (OFHC) ultra-pure copper. The insulation is a foamed polyethylene chosen because it has a suitably high dielectric constant, and is well damped. To ensure excellent strength, two Kevlar® fibres are woven into the cable.

At the amplifier end, the jack is electrically isolated from the amplifier chassis, while on the headphones high-precision self-latching connectors are used to ensure a secure connection. A sense loop built into the cable runs to each ear cup, and if the cable is disconnected at either the amplifier or headphone ends then the amplifier automatically shuts itself down.


Delivering performance without compromise, ESS SABRE reference DACs, an AKM Premium ADC, and custom 64-bit double-precision fixed-point DSP, sit at the heart of a high precision, ultra-low noise, low distortion system.

The Sonoma system supports all of the Hi-Res Audio formats an audiophile would expect from a class-leading audio product.

Discrete Single-Ended Class-A Amplifier

To ensure isolation from all interference sources, the amplifier is encased in a completely shielded, machined aluminium enclosure.

High-performance, single-ended, discrete FET Class-A amplifier with very low distortion and wide bandwidth which is optimally matched to the HPEL.

The Class-A output stage is operated at a high bias level, and delivers a very high slew-rate. Operating at such high bias levels results in improved linearity.

The drive signal has a maximum amplitude of 145 V (rms), which is superimposed on the 1350 V DC bias. Maximum signal of 850 mV (rms).

The amplifier provides the following inputs:

USB 2.0 (digital)

Hi-Res Audio formats up to 32-bit/384 kHz PCM and DSD via DoP (DSD64/DSD128)


Coaxial S/PDIF (digital)

PCM formats up to 24-bit/192 kHz


‘high-level’ RCA (x2) jacks (analog)

Maximum input signal of 2.1 V (rms)


‘low-level’ 3.5 mm stereo jack (analog)

Maximum signal of 850 mV (rms).


ESS sabre reference DAC

The Sonoma M1 system was developed to deliver true high-resolution performance. For the critical digital-to-analog conversion stage, we turned to an established leader in the field. ESS Technology is universally recognised as the world’s premier DAC chip manufacturer, and we have opted for their 32-bit Reference DAC. Two stereo DAC chips are used in a special mono mode to deliver a measured 129 dB signal-to-noise ratio (SNR).

Custom 64-bit Fixed-Point Digital Signal Processing

Helping us to achieve the desired response at the output of the headphone, we digitally process all signals using custom 64‑bit double-precision fixed-point arithmetic, running within a high performance, multi-core XMOS processor. It is well‑known in the field of audio processing that fixed-point arithmetic is best, and the 64‑bit arithmetic used in the Sonoma M1 exceeds the performance of most professional audio workstations. All the filter responses within the DSP are minimum-phase, slow roll-off and are optimised for excellent time-domain response.

Fully-digital interpolated volume control which dramatically outperforms all the pure-analog:

– Perfect left/right channel matching.

– No loss in fidelity and no loss in dynamic range.

– No potentiometer/attenuator non-linearities at the end of range

– No noise issues like ‘zipper’ noise, clicks/pops, etc.

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AKM 32‑bit/384 kHz Premium ADC

All incoming analog signals must first be converted to digital. This is undertaken in a multi-channel 32-bit/384 kHz AKM Premium ADC chip. As the amplifier has both low-level (3.5 mm) and high-level (RCA) inputs, separate ADC channels are used depending on the input selected. The full dynamic range capability of the ADC is achieved regardless of the input selected.

The measured SNR of the ADC stages exceeds 120 dB.

Crystek Ultra-Low Phase-Noise Oscillator

Particular attention was paid to circuit board layout to ensure the lowest noise and distortion levels possible. Through careful component positioning, we were able to maintain an ultra-low noise-floor of -129 dB!

To guarantee the highest performance regardless of the input signal format, the Sonoma M1 is built around an ultra-low phase-noise oscillator from Crystek. Operating at 100 MHz, it features extremely low close-in phase-noise (<90 dBc/Hz) and an industry-leading rms jitter level, at 100 MHz, of 82 femtoseconds (82 x 10-15 s). All clocks used throughout the M1 are derived from this exceptionally accurate master oscillator via a sophisticated clock distribution scheme using Texas Instruments frequency dividers.


Precision CNC-machined aluminium case

A special 3D-wave pattern is then cut into the base and top-plate by CNC-machine to facilitate heat dissipation. Starting with a solid billet of high purity Aluminium 6063. The metal walls which remain are 5/16th of an inch thick. A top-plate of the same thickness is similarly produced, along with ½ inch thick end-plates to form the complete enclosure. To obtain the desired finish in the metal, the machined parts are then blasted under high pressure with fine glass beads before being clear anodized.

The entire M1 chassis is electrically conductive, and acts as an ideal EMI/RFI shield. Care was taken to ensure a low impedance. The signal ground is kept isolated from this protective shield, and all these features together contribute to the ultra-low noise floor and freedom from external interference.

Superior USB Data Cable

In collaboration with Straight Wire Inc., we developed the supplied USB cable. Featuring gold-plated connectors and a silver-plated data path, it is the ideal connection between your digital music source and the Sonoma M1 system.


Custom Universal Power Supply Unit

Custom-designed for the M1. Universal voltage, outboard switch-mode power supply unit capable of delivering about 3.5 times the maximum power the amplifier is designed to draw under steady-state conditions. In addition, the unit uses a fixed frequency-switcher (operating at over 85 kHz) to avoid the possibility of the switching-frequency dropping into the audio band as the power draw changes.

It is connected to the amplifier via a custom, high-quality, shielded cable, and, to ensure an ideal connection, it is fitted with a high-performance, Switchcraft locking DC power connector. A massive ferrite core filter has been added to the DC cable to reduce EMI.



Energizer & DAC