Building powerful amplifiers is a relatively simple proposition. While size and heat dissipation are usually considerations, high-powered amps are available at relatively modest prices. So why do some clearly sound better? The answer lies in the control of the power and the degree to which designers optimize the performance of their chosen technologies.
Solid State Design
Most designers who use solid state devices tend to choose a favorite type of device (bipolar, MOSFET, J-FET, etc.) and design around its known strengths and weaknesses. It's a logical approach, since knowing everything about one type of device is easier than knowing everything about all of them. But the Classé Design Team have decades of experience working with many different devices. They have intimate knowledge of the strengths and weaknesses inherent in solid state devices of every major category. This knowledge enables a more creative design approach, where devices of different type are used to maximum advantage in each amplification stage.
In order to achieve consistently high performance across the entire range of amplifiers, Classé designs are derived from a common platform, sharing common circuit blocks and in some cases, entire channel modules. J-FET devices are utilized in the input stage because of their high input impedance and low offset current. As a result, Classé amplifiers are easy to drive and low-noise, they don't interact adversely with interconnect cables, and with J-FET input stages, require no sound-degrading coupling capacitors.
MOSFET devices, like J-FETs, are voltage driven. They were chosen for the driver stage, where they deliver the necessary voltage gain while also being well-suited to meet the current requirements of the output stage. Bipolars, if driven with sufficient current, are excellent high-current output devices for amplifier output stages. Bipolars are also capable of superior low frequency performance and stability compared with the alternatives. All Classé amplifiers share the benefits of these and other design choices where tradeoffs are balanced to achieve uniquely compelling sound.
Class A
For Classé amplifiers, output stage DC bias is set to idle at a relatively low level to minimize heat. As the output increases under load, the bias increases, remaining at about 1/3 of the total output power. So for example, a Classé amplifier delivering 100W into an 8
load will be operating at about 30W Class A, eliminating any effect of switching distortion normally associated with a Class A/B design.
Power Supply
All Classé amplifiers use custom-designed, high-regulation toroidal transformers for low noise and high current capability under load. These large and expensive parts are protected from potentially harmful in-rush current at turn-on by large, series surge resistors. Each transformer is built with separate secondary windings to enhance channel separation while giving all channels the benefit of the massive, over-built transformer core.
Power supply filtering is taken to the extreme in Classé amplifiers. Large banks of small to moderately sized capacitors smooth ripple on the supply voltage and provide a virtually limitless reservoir of power that can be accessed instantaneously by the audio circuits. It is the combination of speed and total size that make this approach particularly desirable in high-performance amplifiers.
Circuit Management
Building amplifiers with exceptional sound that are also reliable is an illusive goal for many designers. The Classé Design Team have developed new techniques for managing circuits without degrading amplifier performance. Gone are the internal fuses that sometimes act too slowly and degrade sound. Gone are the DC blocking caps, used in other designs to protect loudspeakers from harmful DC. In their place is a control circuit, driven by its own independent power supply, devoted to managing the audio circuits without intruding in the signal path.
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Output current is often required in massive amounts for short periods. Knowing the difference between a large, temporary demand and a shorted speaker cable, allows Classé amplifiers to perform their best and also protect themselves from dangerous fault conditions. Hall-effect rings are used to monitor output current, encircling the conductors without lying in the signal path. Their output voltage is digitized and monitored over time, allowing the amplifier to make an intelligent decision about whether the amplifier is handling a demanding piece of music, or wrestling with a fault condition (such as a shorted speaker cable).
A DC servo is used to correct for DC voltages that could degrade the sound or even harm loudspeakers if allowed to pass. Thermal sensors inside, including sensors on every heatsink, monitor operating temperatures and switch the amplifier off if potentially harmful conditions exist. The AC mains voltage, frequency, phase and ground condition are constantly monitored to be sure that normal operating conditions exist.
The Classé Design Team have developed a robust system for ensuring the optimum operation of Classé amplifiers and adequate protection of your investment. The concept is simple. Classé amplifiers either sound their best, or they switch off.
Advanced Mechanical Platform
In high-performance audio systems, every detail matters, including the chassis that encloses the circuitry. Unwanted vibrations caused by the sound of the system itself, can reduce clarity and resolution through microphonic coupling.
Classé amplifier chassis are made of both steel and aluminum. The front panel wrap is an aluminum extrusion with a broad radius on the front corners. The feet are designed with Navcom™ LimbSaver® material, specially formulated to provide the proper durometer (or stiffness) for heavy amplifiers, to reduce the effects of external vibration. As a mechanical system, the chassis provides a rigid, stable, low-vibration platform for the amplifier circuitry.
Balanced and Single-Ended
All Classé amplifiers provide for both balanced (XLR) and single-ended (RCA) inputs. The LEDs on the front panel tell not only the number of channels, but also their mode of operation. Unlike other designs, Classé amplifiers allow both single-ended and balanced connections to be made simultaneously. For example, the user may choose to connect balanced inputs for the left and right channels of a high-end preamp, while the single-ended connections for these channels are connected to a surround processor. The different inputs can then be selected from the front panel, or by RS-232 via PC or an external control system.
CA-M400
While circuit topologies and most signal path parts are identical across the Delta series amplifier range, the CA-M400 monaural amplifier applies those modules in a more advanced configuration. The 400W monaural amplifier is built using two of the 200W channels in balanced mode. The result is a fully balanced amplifier, more closely resembling Classé’s reference Omega series amplifiers. The CA-M400, at the top of the Delta series range, represents a remarkable achievement in amplifier performance and value.
External Control
Digital circuitry manages monitoring and protection circuits as well as operational controls. These circuits are independent of the analog audio circuits, with power being derived from a separate secondary transformer/power supply. Full control is available from the bi-directional RS-232 port on the rear panel, as well as by IR remote. Controls include: Operate/Standby/Standby Toggle, Mute On/Mute Off/Mute Toggle. Amplifier Sequence Number selection and Channel Input selection are available with RS-232 control. DC trigger inputs are also available for remotely toggling amplifiers between operate and standby.
Value
It is often said that "it's not what you pay, it's what you get." As we developed this latest generation of Classé amplifiers, it was clear that the more we put into them, the better they got and the more value they offered. For a company known for its many successful amplifier designs over more than two decades, we are particularly pleased to have established a new benchmark with our Delta series for contemporary, high-value, high-end electronics.
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