Discrete Single-Ended Class-A Amplifier

Like all electrostatic transducers, the HPEL requires a high-voltage drive amplifier in order to function. In the case of the M1, the drive comes from a high-performance, single-ended, discrete FET Class-A amplifier with very low distortion and wide bandwidth which is optimally matched to the HPEL. The amplifier was designed and optimised to drive the inherent capacitive load of an electrostatic transducer, and 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.

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

Anyone who is familiar with loudspeaker or amplifier measurements will undoubtedly have seen plots of flat frequency response from a few tens of Hz all the way up to 20+ kHz. A flat frequency response is the ultimate goal for those components, and is quite easily achieved in an amplifier, but more difficult to achieve in a loudspeaker, especially in a real-world listening room (as opposed to an anechoic chamber).

Precision CNC-machined aluminium case

In contrast to the M1 headphones, where every effort was made to minimise weight, the M1 amplifier is a very substantial unit. Starting with a solid billet of high purity Aluminium 6063, the material is first extruded, and then CNC-machined to produce a shallow U-shape comprising the base and side walls of the amplifier. 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. A special 3D-wave pattern is then cut into the base and top-plate by CNC-machine to facilitate heat dissipation

• USB Input USB 2.0, type B; accepts digital audio formats up to 32‑bit/384 kHz PCM and DSD via DoP (DSD64/DSD128)

• Digital Coaxial Input S/PDIF; accepts digital audio formats up to 24‑bit/192 kHz PCM

• Analog Input (High Level) Dual RCA; 2.1 Vrms

• Analog Input (Low Level) 3.5 mm; 850 mVrms

• DAC Dual mono, 32-bit/384 kHz DACs with balanced outputs

• ADC 32-bit/384 kHz multi-channel ADC with balanced input buffers

• Digital Signal Processing (DSP) 64-bit (double-precision) fixed-point processing at native sample rates

• Amplifier/Energizer Discrete FET, single-ended, high-bias Class-A output

• Distortion + Noise < 0.05%

• Bandwidth > 65 kHz

• Enclosure CNC-machined 6063 aluminum

• Power Supply External: 24 VDC, 60 VA, fixed frequency, class B-compliant SMPS;

• Internal: fully isolated, ultra-low noise linear regulation

• AC Mains World voltage compatible (90-264 V, 50-60 Hz); IEC-60320 C14, earth-grounded power cable; 1.5 meter length

• Dimensions H x W x D: 57 mm (2.24 in) x 190 mm (7.48 in) x 290 mm (11.42 in)

• Weight 2.45 kg (5.40 lbs)