The BMC Concept:
• No Inflated Retail
• High Value for Money
• Innovative Designs Serving Music
• Benefits in Sound by Technology with BMC sets
B.M.C. Phono MCCI
• Ultra Quiet Performance
• No Load Matching Needed
• Balanced Current Injection Design
• Outstanding Dynamic Performance
• Perfectly Balanced from Input to Output
B.M.C. applies exceptional concepts to their components to make technical innovation and perfection serve music reproduction.
B.M.C.'s Phono MCCI is a truly balanced, global feedback free, passively equalised moving coil phono pre-amplifier with the exceptional Current Injection input and LEF single ended class-A output stages.
Amplifier Features
1. Balanced Current Injection input
2. Common base circuit for highest bandwidth
3. Widely automatic gain adjustment
4. Feedback free circuit with very short signal path
5. Full balanced circuit
6. Balanced LEF single ended class-A output
EQ and Other Options
1. Passive equalisation with the I/V converter
2. Neumann corrected RIAA, or traditional RIAA
3. RIAA options for low end extension and warmth
4. 3 selectable gains
5. Subsonic filter selectable
High End Parts and Exteriors
1. Special ultra-low-noise transistors with very high Hfe, 10 in parallel
2. “Balanced Current” capacitors for precise and colourful sound
3. Induction-free Polystyrene capacitors
4. Metal-thin-film resistors with 0.5% tolerance
5. Fully gold plated 4-layer printed board
6. Copper plated iron shield cover
Amplifier Circuit
“Current Injection” (CI) means a current input, in which the pickup cartridge itself becomes part of the amplifier. The MC-cartridge is a generator injecting its current into a system of balanced DC-currents, directly creating an amplified output voltage. CI uses the original current of the cartridge and therefore the amplified voltage has a very precise analogy to the source signal. Actually this CI is rather an I/V converter than an amplifier in the traditional sense. Dynamic losses and distortions are remarkably lower compared to common voltage amplifiers.
The Current Injection input circuit is an unusual application of the common base circuit, which is known for widest bandwidth, lowest distortion, best dynamics and musical performance. In common applications the disadvantage would be a low input impedance, but fortunately this matches perfectly to our most important audiophile sources: MC-cartridges and current output digital/analogue converter. Already, for decades some, of the best phono MC amplifiers use common base circuitry, but just with the balanced CI input circuit such an idea can be applied without compromise.
The current for the CI-operation is determined by the cartridge's impedance and the phono amplifier's input impedance. This way the resulting gain in a wide range adjusts automatically to different MC-cartridges as a high-output MC may generate a higher voltage, but due to the higher impedance it reduces the current.
The whole signal proceeding is done in two short gain stages. Due to the fact of no feedback there is also no need for excess gain.
Generally there are many ways of designing low-distortion voltage amplifiers, but at lastly there is always a current driver required. Dynamically there are no alternatives to single-ended (opposite: push pull) designs, but those require a mandatory full class-A operation and also deliver higher grades of even-order distortions. LEF (Load Effect Free) applied to a single-ended class-A design avoids distortions by not moving the transistor through it's un-linear characteristic curve. Additionally the fully balanced design widely rejects even-order distortions.
A truly class-A balanced design is a constant non-moving load to the power supply. However much energy one signal requires, the balanced mirror signal requires less. In theory this way there would be no modulation of the power supply by the music signal at all any more, and in our existing applications the power supply modulation is decades smaller compared to an un-balanced circuit.
Furthermore balanced designs have a natural rejection of common-mode power supply disturbances. This results in a remarkably improved “inner quietness” of the music reproduction. In consequence there is more space left for sound details, colours and 3-dimensional sound-stage.
RIAA and Other Options
Due to the absence of global feedback, the RIAA equalisation can not be an “active-type”, which usually would be inside the feedback loop. The precisely made RIAA filters are applied in two decoupled stages in a “quasi-passive” manner, which means a frequency dependent passive I/V converter. Excess gain, which is a traditional disadvantage of common passive RIAA solutions, is not required. B.M.C.'s Phono MCCI combines the dynamic neutrality of a passive equalisation while avoiding excess gain.
The common RIAA rolls off with endless damping for high frequencies. Logically a perfectly matched LP was cut with an infinitive gain before, which is obviously impossible. Consequently the common RIAA is never truly accurate. For the treble emphasis limitation in recording for decades there is a quasi-standard defined by the leading record-cutting-machine manufacturer Neumann. Applying a correction according to Neumann makes a small but very well audible difference in voltage. The correction of the phase shift is even more obvious. Optionally the Neumann-correction can be disabled so it is easy to check out the difference. There is simply more breath and transparency within the music.
For matching cartridges with low-level-extension problems or too less “body” it is possible to extend the lower bass or adding “body” plus lower bass.
Although the gain between different cartridges differs less than usual, according to the construction of the MC there might be level differences. Phono-MCCI allows the setting of 3 different gain levels.
Ideally the cartridge should match to the tonearm and the system is well damped. In other cases a subsonic-filter can be selected.
High End Parts
Phono-MCCI's very special transistors feature a super high Hfe and a super low typical noise figure of 0.3dB which is at the limit of today's possibilities. Each functional group uses 10 in parallel which reduces the statistical noise by 10dB. There should hardly be any more quiet solution for a phono amplifier.
The “Balanced Current” electrolytic capacitors have a balanced characteristic for charge and discharge. The important ESR-bandwidth is far beyond common electrolytic capacitors. This results in an improved musical performance, precision, detail and beauty, starting from the very low frequency, covering the whole spectrum.
Induction-free Polystyrene capacitors feature the lowest losses of all film capacitors and show no resonances. Used in audio circuits they deliver very open and pleasant treble.
Metal-thin-film resistors with 0.5% tolerance represent the highest part level within this group. SMD types do not have clamped contact wires and show lowest inductance.
The core part is build on a fully gold plated 4-layer PCB. The solder is lead-free and includes silver. The sensitive core module has its own copper plated shielding box.
New Standards
The digital music reproduction over the years challenged the analogue technology to deliver better phono components. This improvement process should not be limited by old standards. In this sense an un-balanced phono input and circuitry is no longer state-of-the-art. With all the limits in noise and the related detail resolution it limits in-depth listening. All aspects of the circuitry should serve dynamic fine resolution all-over the whole frequency range for really unveiling the advantages of Vinyl-reproduction. Part of this philosophy is the abandonment of global feedback also for RIAA amplifiers and the related own dynamic actions. Then music can blossom and catch emotionally while being relaxing; leading us into a different world, touches and may seduce us.
B.M.C.'s Phono MCCI is exceptional, and easily among the best MC phono preamps available today at any price. Its sound was startlingly good, and in some ways seemed to surpass that of virtually every other phono preamp I've heard, especially in terms of transparency, and of not imposing its own strong character, or any character, on the music.
- Michael Fremer, Stereophile June 2013
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