The ZeroUno PLUS is a high end pre amp, which can handle all kinds of digital and analog sources.
All analog input signals are operated by a separate circuit implemented in one additional board stacked to the main board of the ZeroUno DAC.
The analog input board comes with a dedicated power supply and works totally independent from the digital circuit of the DAC section.
In addition to the digital inputs of the ZeroUno DAC there are two pairs of single ended RCA connectors for analog sources available on the backside of the ZeroUno PLUS.
The digital interface of the ZeroUno PLUS is exactly the same as that of the ZeroUno DAC. There are digital inputs for S/PDIF signals via RCA, XLR (AES/EBU), TOSLINK or USB in PCM and DSD formats. A true 75 Ohms input via a BNC connector is optional as a replacement for the AES/EBU input.
Both analog and digital signals, managed by the ZeroUno PLUS, are operated by the same tube output stage already introduced for the ZeroUno DAC.
All input signals are coupled to the volume control by interstage transformers custom made by Lundahl for CanEVER AUDIO®.
The volume control module works 100% in the analog domain for both digital and analog input signals. It is based on a ladder network of pure 0.1% high precision thin film resistors for the lowest possible noise, channel separation and perfect balance between the left and right channel and independently from the volume level. With each volume setting selected there are only TWO resistors operating the music signal. In total there are 127 different positions for volume setting in steps of 0.5dB possible, reaching a dynamic range of 127dB!
In addition to the volume control, there is a level control implemented. This feature let the user adjust the signals from all analog and digital sources to exactly the same level to avoid any increase or decrease in loudness while switching between input channels. The level can be adjusted in steps of 0.5dB in a range of -26 to +17dB.
Each input channel can be activated or muted. So the user can toggle between only those input channels, which are actually connected to a source. Or, if the user wants to compare the sound quality of two different inputs (e.g.: analog records vs digital sources), he can mute all input channels beside those two, which he would like to compare and switch only between them.
To switch between the active input channels the user can push the INPUT button on the front plate or use the MENU button on the RC.
Following the volume control stage is the heart of all ZeroUno products: the tube output stage!
The topology of this tube stage is different from standard circuits. Here the two triodes of one 6SN7GT are connected in a way to auto cancelling the residual ripples from the rectifier stage of the power supply. Using this topology the power supply does not need a huge capacitors to filter those ripples. The value of the filter capacitors can be small, because the main filtering is done by the two triodes inside the 6SN7GT.
Described in a more technical way: The design philosophy of the tube output stage works as a single ended stage for the audio signal, but as a “push-pull like stage” for the power supply as the auto cancelling capability of a push-pull circuit regarding the ripples from the power supply is well known.
In total the signal path inside the ZeroUno PLUS is very short and makes use of a minimum number of components for both analog and digital signals.
The final signal of the tube output stage is present via one pair of single ended RCA connectors and a pair of balanced XLR connectors. To balance the output signal a pair of high quality transformers produced by Lundahl due to CanEVER AUDIO® specifications are in use. Both pairs of output connectors can be used in parallel for bi-amping or to connect an active subwoofer.
Finally a few word about the power supplies implemented inside the ZeroUno PLUS.
Basically the power supplies inside the ZeroUno PLUS cover about 70% in number of components and board space.
The digital part of the circuit inside the ZeroUno PLUS is exactly the same as that of the ZeroUno DAC. It consists of 13 separate ultra-low noise power supplies fed by two toroidal transformers followed by a pre-filtering stage plus 13 discrete analog power supplies designed around four AD797 operational amplifiers.
The analog part of the circuit inside the ZeroUno PLUS is based upon three independent power supplies and is designed with the same philosophy in mind as the digital circuit: two dedicated toroidal transformers - one for the analog stage and one for the digital volume actuator – followed by three pre-filtering stages, the left analog channel, the right analog channel and the digital volume actuator, plus two ultra-low noise discrete analog power supplies designed around three AD797 to power the analog circuits.
All analog and digital paths are rigidly separated and powered totally independent to avoid any interference or cross talk.
Finally: All the ZeroUno DAC produced after March 2017 can be upgraded to a ZeroUno PLUS!
- The circuit of the ZeroUno PLUS is based on four integrated hardware platforms: Cirrus CS3308 Analog Volume Control, ESS Technology SABRE32 ES9018S DAC, XMOS XU216-512-TQ128 and Atmega1284p
- For optimum performance the hardware platforms run on a proprietary implementation of special developed firmware, stored in a flash memory, easy to update
- 2 motherboards based on a four-layer PCB with extra thick copper traces to achieve ultra-short signal paths with minimal wiring, to avoid electromagnetic induction of noise and to insure perfect grounding
- Discrete built power supplies for the digital and the analogue section using 6 toroidal transformers, last generation of ultra-low noise rectifier diodes and high quality audio operational amplifiers AD797
- Discrete built ultra linear power supplies for the heating power and for the high voltage of the tube output stage using two toroidal transformers with last generation of ultra-low noise rectifier diodes, double π filter, audio grade resistors and capacitors
- Dedicated discrete filters for digital noise suppression
- Comprehensive noise regulation for all analog & digital circuits
- Analog volume control with digital actuator, with a precision higher than 1/100.000
- Voltage swing at the outputs, balanced and unbalanced, is 3.2Vrms / 9Vpp
- On board output level setup to match different sensitivity of the direct connected power amplifiers
- Input impedance of the power amplifier not below 20Kohm, recommended at least 47Kohm, to do not lose bandwidth
- True Class A discrete built analog tube output stage with zero negative global feedback for use with 6SN7GT tube family, including the CV181 tubes
- Jitter free operation by patented high performance algorithm
- PCM and DSD digital roll-off filters as well as asynchronous sample rate conversion of the Delta-Sigma DACs are Voltage-compensated, ultra-low phase noise and low jitter crystal oscillators (clock) acts as master clock. Two separated clocks for sampling families of 44.1, 88.2, 176.4, 352.8 kHz and 48, 96, 192, 384 kHz
- DAC output stage with shortest possible signal path based on custom made amorphous audio transformers produced by Lundahl with first order discrete analogue filter for best THD and digital noise suppression
- Separately powered USB chip by a “quasi battery power supply” using a 1,0 Farad super-cap to avoid any distortion induced by the connected computer (no connection to the +5V powerline of the USB cable)
- USB input based on XMOS xCore audio chip with bit perfect transfer for 16bit, 24bit or 32bit data in PCM format up to 384 kHz including support for native DSD and DoP
- 4 Digital-Inputs: 1x USB 2.0; 1x true S/PDIF 75 Ohm BNC or, optional, true AES/EBU 110Ohm XLR; 1x S/PDIF RCA; 1x S/PDIF OPTICAL
- USB input compatible with following audio formats via PC and MAC:
- PCM: 44.1; 48; 88.2; 96; 176.4; 192; 352.8 and 384 kHz up to 32 bits
- DSD (DoP): 2.822 MHz / DSD64, 3.072 MHz, 5.644 MHz / DSD128
- SPDIF inputs (AES/EBU, BNC, RCA) compatible with PCM signals from 44.1, 48, 88.2, 96, 176.4 and 192 kHz, up to 24 bits. The OPTICAL input accepts music files with a resolution up to 24/96 kHz
- LCD Display with variable brightness, changing letter size for better reading from listening position
- Infrared remote control with direct function keys for volume, balance, absolute polarity, mute and input switch
- No drivers required for LINUX or MAC OSX - USB Audio 2.0 driver available for Windows XP/Vista/7/8/10
- Dimensions (W x H x D): 400 x 198 x 360 mm
- Weight: 11.5 kg
- Power Supply: AC 220-240 V~ (or alternatively 100-120 V~), 50/60 Hz
- Power Consumption: MAX 30W at startup – MAX 7W after 1 minute (MAX is depending on the tube used)
- Infrared Remote Control: 38KHz - Standard CR2032 battery for the controller
∞ Analog & Digital Inputs
The ZeroUno PLUS offers two analog inputs.
The user can assign an individual name for these inputs corresponding on the type of equipment, which is connected to the individual input. Every time an analog input is selected, the assigned name will presented in the display on the front.
The names of choice for the analog inputs are:
The individual input names can be selected from the SETUP menu!
The digital inputs are:
- 1x RCA, 1x XLR (AES/EBU) and 1x TOSLINK for S/PDIF signals
(optional: 1x BNC instead of the XLR input)
- 1x USB Audio 2.0 port for a direct connection to a computer or a network bridge / streamer
All the S/PDIF digital inputs have a galvanic ground insulation from the connected components.
Each input channel can be activated or muted. So the user can toggle between only those input channels, which are actually connected to a source. Or, if the user wants to compare the sound quality of two different inputs (e.g.: analog records vs digital sources), he can mute all input channels despite those two, which he would like to compare.
Although the ZeroUno PLUS is offering high performance technical data, it is impossible to judge it´s value based on these only. The result of the management of the input signals in the ZeroUno PLUS is a natural, warm, not harsh and a very dynamic sound, which is not polished to exhibit the last possible details, but to let the music play…………..
Looking at directly heated triode based tube amps (e.g. 300B, 2A3 or 211 and 845) or tube amps in general one can make similar observations. From a pure engineering point of view, there is no reason to prefer a tube amplifier over a transistor based amplifier. Most of the technical measurements are even voting against a tube amp. However, if we do not leave it up to the instruments alone to qualify such an amp and instead we use our ears to listen and feel our emotions, the picture in many cases can change a lot!
Have fun with the ZeroUno PLUS!