We introduce our first integrated dual-mono vacuum tubes amplifier based on a modernized Williamson circuit. It is a 27 Watt per channel Push-Pull, operating in ultra-linear mode, optionally switchable to triode mode.
Soviet triodes 6N8S are used as steering vacuum tubes at the pre-amplifier stage. The power stage operates on excellent GU-50 transmitter vacuum tubes, Soviet-made for the military in the 1960s (NOS).
In order to minimize distortion, the power supply is separated from the amplifying section by placing it in a completely separate, screened case.
While designing the circuit we managed to achieve identical topography of the left and right channels, which resulted in a fully symmetrical signal path.
It should be noted that loudness control does not employ a common potentiometer, but a 64-step attenuator (based on relay switches) by Khozmo Acoustic, which minimizes signal inequalities in both channels of the amplifier. The circuit employs a small number of condensers in the signal path, which also improves sound quality.
The web server, audio file player and DAC base on a 24-bit Burr-Brown PCM1794 chip. Inside there is an integrated computer with an SSD disc, connected to a D/A converter board through USB.
PCM 2704 (sampling frequency 32kHz; 44,1Khz and 48kHz) is used as a USB DAC. It decodes the digital signal from the computer into an S/PDF signal, which is then fed into WOLFSON MICROELECTRONICS WM8804 S/PDIF receiver/sender.
WM8804 accepts 16 and 24-bit signals and frequencies between 32 and 192 ks/s.
SRC4192 upsampler converts a 16-bit signal into 24 bits.
The analogue output is built on 6N23P vacuum tubes in SRPP circuit.
Each module: computer, DAC digital section and DAC line section has independent power supply. Management of the computer is performed in open Volumio software on any device with a web browser, i.e. smartphone, tablet, laptop…