NEW CANEVER LASCALA POWERAMP!


"How to design the „perfect“ Amplifier? by Mario Canever; CanEVER Audio. The “perfect” amplifier is basically impossible to design, but with engineering skills based on a strong background in vintage amplifier design AND a deep knowledge of recently developed components as well as modern circuits, it is possible to get very close to an amplifier, which works almost perfectly."


 Fig.1: The ZeroUno PLUS – a Tube Preamp with integrated DAC introduced in 2017

CanEVER Audio, with its smart engineering approach, has already proven that introducing highly competitive products in the overcrowded market of High End Audio is possible. The ZeroUno DAC, introduced in 2016 and the ZeroUno PLUS, shown for the first time at the High End Show in Munich 2017, are a perfect example of this. Both products are a combination of a high quality DAC including full MQA decoding and a preamp with a seriously designed tube output stage working as a current source! While the ZeroUno DAC is a preamp accepting input from digital sources only, the ZeroUno PLUS comes with a top class analog preamp build in, in addition to the ZeroUno DAC circuit.

 Fig.2: The LaScala Power Amp coming in two cabinets containing power supply and the amplifier

During the High End Show 2018 CanEVER Audio will introduce the LaScala PowerAmp to complete the audio chain. The power amp design is the result of over 30 years of research and experience made in the design and building of amplifiers based on single ended, push-pull and hybrid circuits, using tubes and/or transistors.

In the initial design phase of a power amplifier, which type of audio circuit to implement is one of the most important and basic decisions that needs to be made. It was clear from the beginning: Class A mode was essential in order for the sound of the amp to be as natural as possible. To reach a clean sound - free from any distortions - the decision to use a fully symmetric design was the only choice possible. To obtain the best performance in channel separation and power handling, the power supply and the amp itself are designed in a dual-mono configuration, in which the power supply and the amplifier come in two separate cabinets.

Other important aspects of the LaScala PowerAmp design are the absence of coupling capacitors in the signal path as well as any kind of feedback loops.

The amplification of the signals is done by a smart combination of a tube driver stage for voltage amplification, coupled by an interstage transformer to the output stage, which is based on the latest generation of MOSFET ́s for the current amplification. Both stages operate in push-pull mode. Output transformers couple the current stage to the connected speakers in order to match the output impedance of the MOSFET ́s to that of the speakers.

The CanEVER Audio LaScala PowerAmp is running in pure Class A mode. It delivers 50W or 90W per channel depending the settings done by a switch on the backside of the power supply.

Fig.3: Transformers used inside the LaScala PowerAmp

Another important aspect worth noticing is that the La Scala Power Amp works as a current source amplifier, which guaranties the capability of the amp to drive all kinds of loudspeakers – even those with an irregular and current demanding impedance curve across the listening bandwidth.

What makes the LaScala PowerAmp truly unique and different from “similar” designs available on the market are microprocessor driven, “Bias Control Circuits”, that constantly control all stages of the amp. Without the firmware to run those microprocessors, a design like the LaScala PowerAmp would be impossible.

The LaScala PowerAmp created by CanEVER Audio is a power amplifier resulting from the combination of engineering skills in the technology of tubes and transistors, a deep knowledge in computer programming and the design of high quality linear power supplies as well as transformer winding.

You can have a look at the extreme low number of parts forming the amp in the figure below:

 Fig.4: The Basic Circuit of the LaScala PowerAmp (one Channel)

So let us start to have a deeper look at the main building blocks of the LaScala PowerAmp.

THE POWER SUPPLY

As with any other electronic device, the power supply is the heart of a power amplifier. Without a properly designed power supply, a power amplifier will never reach its full potential.
The primary design goals for the power supply of the La Scala PowerAmp were to create an extreme clean DC as well as fast current delivery, even while performing the most demanding dynamic musical program.
Fig.5: The Circuit of the La Scala PowerAmp Power Supply

The two channels of the amp make use of two separate power transformers, each preserving a power reservoir of 900VA!

The type of diodes forming the rectifier bridge represent the latest technology. They have no recovery at turn-off and their “ringing patterns” are negligible.

In the next step, the DC passes a CLC filter, where the inductor of that filter has a value of 40mH. The special winding of those inductors follows very strong tolerances, leading to a high bandwidth. The capacitors of the filter are types of high quality, long life industry grade to manage high current in high temperature environments.

Finally, there is a shunt filter, which acts as a low pass filter based on a capacitance multiplier architecture representing a filter capacity of about 470.000uF.

Although it is not a quality spec per se, it is worth mentioning that the weight of the complete power supply of the LaScala PowerAmp alone is about 25kg!

THE VOLTAGE AMPLIFICATION

The voltage amplification is based on two high gain 6N6P tubes in a specially designed push-pull configuration, followed by an interstage transformer.

THE CURRENT AMPLIFICATION

The current amplification inside the La Scala Power Amp works with a pair of last generation MOSFETs, with a high linearity in the audio band. Using the MOSFETs as a current amplifier only, the driving troubles of the MOSFETs in the classic configurations are avoided. In this way, the interface with the tube voltage driver is excellent.

THE INTERSTAGE TRANSFORMERS

The interstage transformer separates the voltage driver stage from the current output stage and, as no coupling capacitor is needed, preserves the dynamics of the audio signal. That transformer is wounded on a 75% nickel double C core to use in audio applications. It works as a phase splitter to drive the output stage. The special winding scheme creates a perfect symmetry on its secondary side. This allows the use of one pair of IDENTICAL MOSFET transistors, different from usual push-pull configurations, where the mix of not perfectly matched n-type and p-type transistors are standard.

Because the configuration of the MOSFETs, the interstage transformer has to transfer only a voltage signal and not any current. The dynamic and transparency is better preserved benefitting a natural sound.

THE BIAS CONTROL CIRCUITS

A basic problem in push-pull configuration is that the two active components in those circuits (whether tubes or transistors) NEVER come with exactly the same specs. As a result, an amp like this creates additional distortion, which need to be avoided.

Inside the LaScala PowerAmp, the microprocessor-based BIAS CONTROL CIRCUITs manage the current and the voltage stage constantly, to make sure that all parts of the push-pull circuit work always in a perfectly balanced and symmetric way. Important: The BIAS CONTROL CIRCUIT does NOT affect the audio signal nor creates any feedback loop!

THE OUTPUT TRANSFORMERS

While standard in most tube amps (beside OTL designs), in power amps based on transistor circuits there are only a few companies worldwide using output transformers. The benefits of those transformers once they are skillfully designed and wounded are well-known facts to most of the experienced designers. However, to find a manufacturer, which is skilled enough to produce those transformers in high quality - especially the high bandwidth needed – is not an easy task. Finally, the cost, weight and size prevent most companies to make use of such transformers.

The main purpose of the of output transformers is their capability to “transform” the output impedance of the power amp to match with the impedance of the connected speakers. In tube amps, the output impedance of the circuit can be several hundred ohms compared to the 4/8 Ohms of the speakers. In MOSFET based amps, there is still an output impedance of about 30/40 Ohms, which needs to be matched with that of the connected speakers.

As result of the impedance matching based on output transformers, the amp can work at higher voltage and lower current! The less current is drawn from the power supply, the less distortions are created by the switching of diodes inside the bridge rectifier.

Furthermore, the output transformers in a push-pull design, as that of the La Scala Power Amp, cancel effectively any distortion created in the power supply by the design. This effect reduces the values needed for the filter capacitors in the power supply, which, in return, decreases the current needed for charging those caps and leads to further reduction of noise created by this process.

Since the primary and the secondary windings of a transformer are not physically connected, no DC voltage can reach the output connectors of the amp. Therefore, a coupling capacitor, usually implemented at this point of the circuit to block DC from the outputs, but having negative effects on the sound, is NOT necessary inside the LaScala PowerAmp!

HOW TO GET OFF THE HEAT?

Beside the many benefits regarding sound, an amplifier running in pure Class A mode gets very hot! To make sure a long-lasting lifetime of the electronics and a stable running amp, is a true challenge for the designer. That’s, why most Class A amplifiers come with huge heat sinks, which in many cases get still very hot and are unappealing to the eyes. For the La Scala PowerAmp the design goal was to use smarter solutions to reduce the heat from the amp.

Fig.6 and 7: Combination of Heat Sinks and Heat Pipes to cool the La Scala PowerAmp

The pictures above show a row of four heat pipes, including temperature controlled vans mounted from the downside, and four massive heat sinks mounted on top of the MOSFETs. Looking at the LaScala PowerAmp from the outside, only the heat sinks on top are visible. The elegant style of the cabinet gives no sign that a massive Class A amp is hidden inside!

CONCLUSION

With the LaScala PowerAmp, CanEVER Audio has once again proven its skills in offering extremely innovative products to the world of high end audio. Thanks to the ability to combine well-known and proven engineering concepts with innovative ideas, CanEVER Audio has been able to create a product with amazing sound quality, able to compete with the best amps on the market today.

For further information about the La Scala PowerAmp and other products from CanEVER Audio, please visit our website www.canever.eu or send your request to sales@canever.eu
During the High End Show 2018 in Munich You are welcome in our booth P08 in Hall 3!