ZeroUno DAC-HPA - DAC & High Power Digital Preamplifier & HEADPHONE amplifier
The ZeroUno DAC-HPA represents a top-quality DAC based on the well accepted ZeroUno DAC - a strong headphone amplifier running in pure Class A and a remote controlled preamplifier, able to drive any power amp or powered speaker – all in one box.
The building blocks of the ZeroUno DAC-HPA are based on a set of high-performance power supplies, giving each part of the machine a rock solid base to perform at top level. Looking at the boards inside the ZeroUno DAC, one can identify almost 70% of their space covered by the circuits for the individual power supplies. For more details about the design of the power supplies for the CanEVER Audio product line, please refer to the detailed technical descriptions of the ZeroUno DAC or the LaScala PowerAmp.
Special care inside the ZeroUno DAC-HPA has been taken to achieve short signal paths with a minimum amount of high-grade components. You will especially experience this in the headphone amplifier since there are no coupling capacitors used in the signal path, and all circuits are free of feedback loops.
Input Connections: 1xUSB, 1x SPDIF via RCA, 1x AES/EBU via XLR and 1x SPDIF via OPTIC
Output Connection: 2x Pairs of unbalanced RCA-Connectors: 1x Direct DAC Output and 1x Preamp Output,
(optional: Preamp Output XLR / balanced)
The CanEVER Audio ZeroUno DAC-HPA is a:
- top quality DAC based on the circuit of the ZeroUno DAC
- headphone amplifier with connections for unbalanced AND balanced connections
- digital preamplifier including remote control with functions for:
volume, balance, absolute phase, input & mute
The analog output stage is based on a discrete topology without operational amplifiers and runs in pure Class A mode.
There are two pairs of RCA output connectors:
One pair of outputs gives access to the analog signal directly at the D/A stage.
The other pair outputs the amplified signal of the preamp stage.
The output stage is designed as a current source with low output impedance able to drive power amps or powered speakers directly, if needed.
The headphone amplifier inside the ZeroUnoDAC-HPA is a dual mono design with a super-linear driver, delivering power of 2,5 Wrms even into 30 Ohm per channel in pure Class A.
The complete signal path inside the ZeroUno DAC-HPA consists of a very limited number of components.
In the amplifier stage there are no:
- integrated circuits
- feedback loops
The ZeroUno DAC-HPA´s DAC board is based on the same topology as the ZeroUno DAC. The differences between the ZeroUno DAC-HPA and the ZeroUno DAC is the analog output stage. The amplifier inside of the ZeroUno DAC-HPA is based on the same concept as the CanEVER Audio LaScala PowerAmp. It is designed as a small dual mono power amp running in pure Class A mode, which delivers an output power of 2,5 Wrms per channel. The amp can drive both, any headphone in the range 30ohm – 600ohm and as well as power amplifiers or powered speakers.
All the design ideas that made the ZeroUno DAC a well respected DAC, at the top level of performance in the market, are present inside the ZeroUno DAC-HPA, as well. The heart of the DAC board is an ESS Sabre32 ES9018S chip, with its eight differential DACs used in a quad-sum configuration. The digital and analog filtering are a special design of CanEVER Audio and incorporate a dedicated output transformer topology inside the D/A interface.
The layout of the main board inside the ZeroUno DAC-HPA is the same as the ZeroUno DAC to keep the “no noise” performances from the original circuit.
The use of several different ground planes shields the unit from electric noise coming from outside and isolates the individual modules inside the ZeroUno DAC-HPA like “islands interconnected by bridges”.
All digital inputs of the ZeroUno DAC-HPA are the same as the ZeroUno DAC. The new USB receiver board incorporates full MQA functionality. The USB board is powered in “battery mode” and comes with a galvanic isolation from the connected computer or streamer. These additions avoid any injection of noise by the external digital sources.
The design philosophy of the output stage for the ZeroUno DAC-HPA is very similar to the CanEVER Audio LaScala PowerAmp. The output stage is a Class A Single-ended Push Pull circuit with a high current audio line amplifier – capable of driving even low impedance headphones or in general, any heavy load as a power amplifier.
The topology is N-NFB (No Negative Feedback) to reach the maximum “naturalness” of the sound reproduced. The topology is classic with a complementary JFET input stage followed by a transistor acting as a driver and a transistor acting as power device.Special care has been taken to avoid the distortions created in a N-NFB solution using a JFET/transistors topology.
In the picture on the left, one channel is shown with the power transistors soldered at the backside of the mainboard.
Super Linear Configuration
A lot of effort was spent to setup a super-linear circuit that overcomes the non-linearity problems of the above described circuit. The concept is based on the crossing of the driving signals, so that distortions will be naturally cancelled when summed at the push-pull driver in the output stage.
In this manner, the non-linearity of the JFETs and BJYTs are absorbed by a reverse non-linearity mode. This technique is not new and implemented with success in very low noise application requiring high linearity.
In a classic push-pull configuration only even harmonics are cancelled leaving only the odd ones present. With the crossed-driver topology (aka “reverse non-linearity mode”) and the selection of the components within a tolerance of 0.1%, the odd harmonics are “cancelled”, as well. Finally, this leads to a “super linear” topology.
Using a feedback network, reduced distortions could be reached as well. But, while “feedback” seems to be simple and inexpensive to implement, it comes with a price. Implementing “feedback” reduces the “natural sound.”
Extended listening tests have proven that feedback loops tend to create certain “patterns” inside the reproduced music, which do not sound pleasant to the ears (better: the brain) of the listeners.
For this reason the feedback in the topology of the ZeroUno DAC-HPA is avoided.
Implementing the crossed drivers of the super linear topology, the stability and the linearity of the amp implemented inside the ZeroUno DAC-HPA are astonishing even. Deleting the feedback loops and capacitors from the signal path let the sound become more “real” and relaxing.
The drawback of this kind of implementation, is the need for carefully selected JFET and BJT in pairs combined with high quality power supplies of laboratory standard.
The selection process starts from groups of 1000 BJT and FET, ending up at only 20 to 30 transistors suitable for the amplifier.
All the solid state devices are specific for audio use and not simple “industrial” components.