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La Scala Power Amplifier

The Interstage Transformer

The interstage transformer separates the voltage driver stage from the current output stage. As there is no coupling capacitor, the dynamics of the audio signal are preserved. This transformer is wound up 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 bifilar winding scheme creates a perfect symmetry on its secondary side – in other words, the interstage transformer creates two signals as a “mirror image” of each other. This allows the use of one pair of IDENTICAL N-Type MOSFET transistors, different from usual push-pull configurations, where the mix of not perfectly matched n-type and p-type transistors are standard. 

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

Why is this Type of Interstage Transformer so important?

Usually push-pull configurations make use of two “complementary” types of transistors – “N” type and “P” type. Unfortunately, the specifications of those devices are NEVER exactly complementary! This creates some very “nasty” types of distortions in a push-pull amplifier.

As the interstage transformer inside the CanEVER LaScala PowerAmp creates two “mirror images”, it is possible to use two power transistors of exactly the same type. CanEVER Audio uses two lateral N-channel MOSFETs of the latest generation. This type of MOSFET does not need any kind of feedback for the thermal stabilization!

Class A Mode

As all stages inside the power amp are running in pure class A mode, no distortions are created in the crossover section. Specially designed BIAS control circuits manage the symmetry of the signals of the tubes and the MOSFETs. The result is a perfect symmetry in the processing of the audio signal, even if some SPECs of the active element are different. The BIAS for all stages is fix without feedback. The individual BIAS is independent from the power generated, the impedance of the connected loudspeakers and the processed audio signal!

The BIAS Control Circuits

The BIAS Control Circuits - CanEVER AUDIO®

What makes the LaScala PowerAmp truly unique are the microprocessor driven “Bias Control Circuits”. These constantly control all stages of the amp. Without the firmware to run these microprocessors, a design like the LaScala PowerAmp would be impossible.

A basic problem in any push-pull configuration is that the two active components in these circuits (whether tubes or transistors) NEVER come with exactly the same specs, even if they were paired before and, last but not least, they always work at a different temperature because of the position at the heatsink. 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 always work in a perfectly balanced and symmetric way. Important: The BIAS CONTROL CIRCUIT does NOT affect the audio signal NOR create any feedback loop at the audio frequencies! It works below 0.1Hz, or, in other words, with a time constant of 10 seconds.

As a special feature, the microprocessors running the BIAS modules offer the functionality to switch the output power of the CanEVER LaScala PowerAmp between 50W and 100W per channel even while switched on. As the electric circuit is “floating”, it is possible as well to switch (bridge) the amp from 2-channel STEREO mode into one channel MONO mode. Of course, in this mode the LaScala PowerAmp delivers DOUBLE the output power compared to that in the 2-channel STEREO mode.

On the left the "tracking" BIAS Control Units inside the LaScala Power Amp

The result is a perfect symmetrical design with a minimal amount of components in the signal path, which minimizes odd order harmonics usually “hurting” our ears during listening.

A minimal number of parts in the signal path

The LaScala PowerAmp is made of two amplification stages only – one for voltage and one for current. Please note that there is NO CAPACITOR and NO FEEDBACK implemented in the complete signal path!