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ZeroUno HPA

Super Linear Configuration

Super Linear Configuration - CanEVER AUDIO®

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.

Dual Mono Power Supply

Dual Mono Power Supply - CanEVER AUDIO®

The power supply is completely dual-mono, with separated transformers for different power rails. In total six toroidal transformers are used to power the unit.

The picture to the left shows the power supply of one channel, only.

The output is protected against any DC current that might flow at the output in case of a fault. A double contact relay opens and protects the circuit, if needed.

The circuit is also active when the ZeroUno DAC-HPA is powered on or off to protect the attached headphone from the transient noise of the power supply.

This circuit is not part of the signal path!

Grounding and Topology of the circuits

When implementing an audio circuit without feedback loops, the realization of some areas inside the product

have to be treated with special care:

  • the layout of the printed circuit boards
  • the topology
  • the grounding

The final implementation of the headphone amp and the analog output stage of the CanEVER Audio ZeroUno DAC-HPA is the result of many prototypes and associated listening sessions. It incorporates years of experience in the design of amplifiers of any kind, whether tube or transistor based, push-pull or single ended etc.

Inside the cabinet of the ZeroUno DAC-HPA there are two boards stacked above each other. First, there is the main DAC board, which is the one of the ZeroUno DAC minus the components necessary for the tube output stage, including the heating system for the tubes itself. Also, there is the amplifier board that includes the discrete Class A analog output stage. In between both boards is a massive sheet of aluminum. The aluminum plate acts as a heat sink for the four transistors of the Class A headphone amp and shields the analog amp from the digital noise radiated by the DAC board, below.

Protected output

Protected output - CanEVER AUDIO®

The output is protected against any DC current that might flow at the output in case of a fault. A double contact relay opens and protects the circuit, if needed.

The circuit is also active when the ZeroUno DAC-HPA is powered on or off to protect the attached headphone from the transient noise of the power supply.

This circuit is not part of the signal path!

Finally: How does it sound?

Pure Class A amplification with a super-linear driver, no capacitors or integrated circuits in the signal path and no negative-feedback with ability to drive loads even below 30ohms. It really comes close to his “brother” the CanEVER Audio ZeroUno DAC.

Art Dudley wrote about the ZeroUno DAC in his STEREOPHILE review:

 “ But while more flexible choices abound, and while cheaper choices are also thick on the ground, I've heard no other digital product that succeeds quite so well as the ZeroUno at letting music sound like music!

Strongly recommended.