ZeroUno PLUS is a preamplifier with integrated the popular ZeroUno DAC. The tube output stage designed by CanEVER AUDIO® has got the same design philosophy as that of the popular ZeroUno DAC.
At the time, when the ZeroUno DAC was introduced, the main design goals of CanEVER AUDIO® regarding that product have been explained in detail. Now the ZeroUno PLUS comes with all the building blocks making the ZeroUno DAC a great digital preamp, while adding a high end analog preamp section with two analog inputs inside the same cabinet.
Now the ZeroUno PLUS can act as the central preamp in a modern high end audio system to connect all kinds of digital AND analog sources!
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.
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!
FULL TECHNICAL DESCRIPTION HERE