While the ZeroUno DAC acts as a stand-alone DAC as well as a remote controlled digital pre amp, the ZeroUno PLUS comes with a fully fledged analogue pre amp section on top of the digital main board of the ZeroUno DAC packed in the same cabinet.
The ZeroUno PLUS has been designed, to work as a top class pre amp with digital and analogue signal processing including a remote control for all important commands (like: Volume, Balance, Mute, Input and Phase) to be operated from the listening position. Same as the ZeroUno DAC, the ZeroUno PLUS offers four digital inputs (S/PDIF; AES/EBU; TOSLINK and USB) and in addition to those two pairs of RCA input connectors for analogue sources as well as two pairs of analogue output conncetors: 1x unbalanced RCA and 1x balanced XLR. All connectors are professional NEUTRIK connectors from Germany. In a cabinet made of high grade aluminium coated with several layers of metallic paint and coated with a surface of additional two layers of transparent acrylic.
Its internal electronics make the ZeroUno PLUS a digital and analogue pre amp to operate as the central component in a high quality audio system. As a basis of all following circuits there are not less than 6 separate power transformers, which feed the all linear power supplies of the digital and analogue parts of the DAC, the heating and operating power of the tube output stage as well as the analogue board and its special volume control. Based on those power supplies there are in total 13 separately regulated power sources to drive the individual circuits. As the central “brain” for the DAC inside the ZeroUno PLUS, there is acting the ES9018S from SABRE using the same firmware developed individually for this chip by CanEVER Audio.
All incoming analog signals as well as those prepared by the DAC stage are amplified by an interstage transformer, which is produced By Lundahl based on CanEVER Audio specifications. Due to this, the signal path inside the pre amp stage is very short and phase shifts usually created by capacitors in the signal path are reduced to a minimum.
The volume control is another special feature of the ZeroUno PLUS. Usually for the volume control in a pre amp or integrated amp there are used potentiometers. But even high quality potentiometers often cause different levels of attenuation at lower levels shifting the balance of the stereo image as well as limiting channel separation. Instead, some manufactures of high end audio gear use stepped attenuators made of discrete resistors. Based on their mechanical construction those switches offer only a limited number of steps, which makes it difficult to adjust the volume exact to the desired level. Unfortunately, in the long run those switched attenuators tend to have problems with increased contact resistance too. The ZeroUno PLUS uses a different technical approach to reach a high quality volume control. The heart of that control is the CS 3308 chip from CIRRUS LOGIC. Also for that chip CanEVER Audio developed a proprietary firmware to control it. Inside the CS3308 there is a ladder of high precision 0.1% resistors. Simply speaking, the firmware running that chip, selects for each value of volume only one single thin film resistor per channel. This leads to a difference of volume between the two stereo channels of 0.005 dB independent of the volume level! Defined by the firmware, each step for the volume is set to 0.5 dB. Based on the very low thermal noise of the integrated ladder of resistors the volume control of the ZeroUno DAC reaches a level of 0.0001% for THD and a dynamic range of 127 dB. To avoid any kind of electronic noise induced into the music signal, the circuit for the volume control is based on a separated power supply using another isolated power transformer. Described in musical terms: based on these specs, the ZeroUno PLUS offers a very precise and acoustically transparent volume control resulting into a surprisingly wide and deep soundstage.
Beside the precise volume control, the CS3308 offers a level control for all input channels as well. Supported by the set-up menu the user can easily adjust the level of all input channels to reach a perfect balance between the connected sources while switching between the different input channels. For convenience, the user can assign to each input channel a special label like: TAPE, PHONO or TUNER as well as LINE 1, LINE 2, AUX 1 oder AUX 2. Those labels will show up in the display in tall letters each time the corresponding input has been selected.
Furthermore, the user can mute those input channels, which are currently not connected to a source. Last, but not least, for better comparing the signal quality of two connected sources (e.g.: CD player vs. analog record playback) only those two channels are activated in the set up menu. Then the user can toggle between those two inputs by simply pushing the input button on the remote control of the ZeroUno PLUS. After the volume control, the signals reach the tube output stage of the ZeroUno PLUS. The specific way, in which both double triode systems inside the CV181 (compatible with the 6SN7 family of tubes) are connected, lead to a very high signal to noise ratio of that output stage. Independent measurements have shown a S/N ratio of about 110 dB. The tube output stage of the ZeoUno PLUS is designed as a current source with a low output impedance.