CS3-Front-1

 

B.M.C. CS3 Stereo Amplifier

B.M.C.'s CS3 is a Load-Effect Free (LEF) Amplifier with an option to upgrade it to an LEF Stereo Power Amplifier. The crucial secret of the CS3's sound is that it avoids distortion, instead of compensating for it through a negative feedback loop.

LEF = Load Effect Free

The CS3 is a power amplifier without a preamplifier for a short, pure signal path. It features a Volume Control using our exclusive Discrete Intelligent Gain Management (DIGM) system, and an input selector. The lossless DIGM volume adjustment eliminates unnecessary signal attenuation at the input, as well as unnecessary high amplification.

 

CS3 - Rückseite

Aluminium FernbedienungA massive Aluminium made remote control for your convenience of use with a statement of build quality in your hand.

Combining the CS3 with a B.M.C. Digital-to-Analog Converter (DAC) transforms it into a LEF stereo power amplifier that offers DIGM gain adjustment set by the DAC's volume control. In addition, B.M.C.'s balanced Current Injection (CI) input enhances the immediacy of reproduced music by processing the signal current of the source until it reaches the speaker's output voltage. B.M.C.'s LEF output stage avoids distortion before it occurs by relieving the sound-critical LEF single-ended Class-A transistor of all duties other than providing perfect signal reproduction.

Unlike other amplifiers, an LEF amplifier handles a speaker's current demand separately from the voltage demand. The result is an unparalleled mastery of musical complexity that brings to startling life delicate details, rock-shaking power, high dynamics, sonic vitality, and accurate imaging — all on a three-dimensional soundstage.

Load-Effect Free amplification is a new experience that must be heard to be fully appreciated.

The CS3 also boasts solid output power: 2 x 200 watts into 8 ohms, and 2 x 350 watts into 4 ohms.

An electronically stabilized power supply with a 2kW toroidal transformer and balanced current capacitors provide the muscle behind the music.

 

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B.M.C. Audio
CS3 PDF-Catalog

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LEF Amplifier

An innovative, naively low-distortion amplifier circuit without overall negative feedback loop.

Audio engineering gets exciting when following a completely new path with new challenges. There truly was a need for a better solution for music amplification, simply by realizing that the claim of negative feedback loop circuit amplifiers is the complete correction of any error, which implies all those amps would sound perfect and exactly the same - Obviously this was never even close to be true. In the 1990's Carlos Candeias did extensive research for analyzing and improving the dynamic behavior of a negative feedback loop. But after some successes with improvements he realized that this is a dead end of eternal compromises, which is not the aim of high-end audio representing the spirit of true natural music reproduction.

 

Open Amplifier

 

A fresh approach and a new idea led to a new circuitry which solves the distortion problems by removing their cause, instead of trying to correct distortion afterwards. Therefore a negative feedback loop is obsolete with all it's unwanted "contributions" to the music reproduction. This revolutionary circuit we call LEF = Load Effect Free, since the music signal voltage source, which determines the sound quality, is freed from voltage and current swing, so it perfectly delivers the music signal to the speakers.

The significant transistors just care about the music signal, but never delivers any power. Everything related to power is handled by separate external circuits and the unloading of power from the signal voltage source removes the cause of distortion.

LEF amplifier deliver signal voltage and current from separate sources, phase independent! Beside avoiding distortions this also delivers a superior control of the speaker.
This is the basic working principle of LEF = Load effect free.

 

Kringel

 

All About the Music

The consequences of designing an amplifier for consistent, exceptional musical reproduction also lead to test results right out of the textbooks. But the essential thing is the musical experience. The expression "neutral amplifier" makes one think of an amplifier without a character of its own. But it's this lack of characteristics that makes describing the B.M.C. amplifier so difficult, since it can sometimes be brutally dynamic, sometimes highly expressive and full of detail, sometimes raw and discordant, sometimes bewitching and seductively beautiful, detailed and enveloped by its spatial presentation.
In the end, the result is a musical transparency that has never before been heard.

"More of the music and less of everything else."
- Mark Mickelson, Editor, The Audio Beat -

DIGM Volume Control

DIGM = Discrete Intelligent Gain Management

DIGM replaces a traditional lossy volume control in an audio system, delivering a significantly better performance.

Gain control instead of signal waste

The basic idea of DIGM is very different to a traditional sound degrading volume control: The precious source signal does not get divided, but is fully used. Instead DIGM controls the amplification factor of the amplifier (gain) in a way that just the gain needed for the selected volume is applied. Since after the DIGM there is no further gain stage the output noise gets reduced proportionally with the volume level. You experience more quietness.

DIGM Noise

Since normal amplifiers always deliver the maximum signal gain including some headroom, DIGM is improving the sound quality simply due to the fact that lower gain delivers higher signal quality.

DIGM-Diagram

Precision:

Via bipolar transistors DIGM switches precise resistors in different combinations for matching the desired amplifier gain. This way, the input current is turned into the kind of voltage that corresponds to the required speaker output voltage and is adjustable in steps of 1db (PureLine 1.5dB). Since integrated CMOS digital potentiometers cannot be used here because of high requirements on current and voltage strength, a circuit was especially tailored to meet these demands and implemented in SMD equipped modules.

 

Power Supply Concept

M3, CS3The power supply is not the actual amplifier circuit, but has the sole purpose of supplying the amplifier with the necessary energy without contributing any character of its own. This is why the concept and design of the power supply is so very important to the ultimate result offered by a power amplifier.


The requirements can be summarized as followed:
· Low noise and ripple on the DC power
· No voltage drop under load
· Low impedance
· Linear impedance vs. frequency

Kringel
B.M.C.'s M3 and CS3 belong to the absolute world class level concerning power supply size and concept.

A 2kW toroidal transformer is the solid base for a very powerful, dynamic and stable energy supply. Extraordinary musical expansion and transparency are accomplished by storage in a whole battery of custom made Balanced Current capacitors. These exceptional capacitors have the ability to support tonal precision as well as acoustic splendor, and they have a higher degree of purification when confronted with power interferences. However, in contrast to preceding filters they do not achieve this at expense of dynamics, quite the opposite is the case.

An innovative stabilization circuit, even in the power unit, filters remaining power supply ripple and other disturbances out of the supply voltage and keeps it constant even under changing load conditions. The circuit is designed to have low impedance across the full frequency range, so it does not restrict dynamics or interfere tonally with the audible range.

Supply1Neutrality and Quietness

In addition to a large capacitive smoothing the M3 and CS3 have an unique active virtual capacity circuit with a constant current capability of 72A and a peak current of 250A! This circuit eliminates the usual ripple and reduces the noise dramatically. It also minimizes the load voltage drop (reduced from about 4V to 0.3V) and delivers a wide bandwidth flat
low impadance, without the typical inductance of large capacitors. Almost all classical power supplies get inductive and thus unstable within the audio range! Any voltage drop of non­linearity of the impedance directly degrades the sound quality.
The high current headroom reduce the parameter changes for variable loads like music to a minimum. The low­ power and logic part of the amplifier have separate supplies and regulators for avoiding power modulation by the high­ power trunk.

 

Power Supply Ripple:
Ripple

Stability vs. Load:
Power Supply Drop

Impedance vs. Frequency:
Supply Impedance

The extremely sophisticated, stable, clean and unique combination of 2kW toroidal transformer, complete equipping with custom­made "Balanced Current" capacitors, electronic stabilization for the whole amplifier constitutes the foundation for profound quietness and unrestrained vitality. This way, explosive dynamics and energy, as well as fine details, focus and magnificent tones can evolve from a pitch­black background.

B.M.C. Audio

The Sound of Nature