The B.M.C. MCCI Signature ULN is a balanced, passively equalized moving coil (MC) preamplifier lacking negative feedback. It features natural distortion-free and Load-Effect Free single-ended Class A output and a Current Injection input, which optimally reads the signal current of the moving coil cartridge.

The MC System at CI Current Input Compared with Voltage Input

When amplifying a signal from an MC type cartridge, the interaction between the MC cartridge and the input is a critical element, due to the very small MC signal output and it's electromechanical characteristic. Let us compare the traditional voltage input with the CI current input in terms of signal strength, damping, and amplification:

1. Signal Strength:

Comparing Moving Magnet (MM) and Moving Coil (MC) Cartridges at voltage and current Inputs MM cartridges have the advantage, at the voltage amplifier input, with an output voltage almost ten times higher than MC cartridges. It is the other way round at the CI input: MC cartridges can provide up to ten times higher currents than an MM cartridge, while also delivering low inductance. Consequently, an MC cartridge is the stronger not the weaker system at the CI current input.

2. Damping an MC Cartridge as an Oscillating System

A phono pick-up cartridge is an oscillating electro-mechanical system. Using a voltage input, the cartridge voltage signal will be read, but the cartridge emits practically no energy to the amplifier circuit. With a high-impedance input, the oscillation energy of an MC cartridge stays undamped and is especially noticeable in the high-frequency range. Cartridge loading resistors are connected in parallel to the input to damp these oscillations. Music signal energy is always wasted in these resistors, so optimising a system is a compromise: The resistance must be low enough to damp system oscillations to a bearable level, yet high enough for the system not to sound completely de-energized.

At the other end of the transmission path, with an amplifier driving the speakers, there is good reason not to use an amplifier with a high-impedance output, and to connect parallel resistors to damp the natural oscillation of the speakers. Power amplifiers which simultaneously drive the speakers and, through their low-impedance output, dampen their oscillations, are a well established standard which makes perfect sense: Driving and damping the speaker as an oscillating, electro-mechanical system goes hand in hand.

Using a low-impedance current input is unusual but makes perfect sense for the use of MC cartridges: Signal processing and damping the oscillating electro-mechanical system through an amplifier input allows the MC cartridge's energy to flow as current into the input. Energy is discharged this way but not destroyed. In fact, it is used for signal amplification and to create a vitality in sound not previously heard.

3. Use of the Original Input Signal Current

The original current that the MC cartridge feeds into the low-impedance CI input flows right through the amplification stage. At its end it creates a defined signal voltage through the termination. The termination can be a simple resistor, or in regard of phono usage, a part of the RIAA filter network. At the CI circuit output, you can actually find the same electrons that has been fed into the input. The original signal is used instead of a copy. In this way, the very delicate, finely tuned MC signal experiences the most sensitive method of amplification, and is conserved in all its richness and tonal diversity. The wakest point of the MC voltage amplification has been turned to a virtually lossless amplification by the CI (Current Injection) technology.

ULN Advantage

Already the predecessors of the MCCI Signature ULN were considered to deliver a very low noise floor and, according to the German Stereo, even "close to the laboratory record". On top of that the new ULN version delivers another dramatic improvement in noise. This is important because it represents the main disadvantage of MC cartridges, which is now completely eliminated, since only the remaining noise of the empty groove represents the limit of silence.
Here is an illustration of the difference from the previous version:

 

Explanation: A 1 kHz test tone is used which is set to 0 dB. Then the entire frequency spectrum is measured. In the impossible ideal case, there would be nothing else than the tip at 1 kHz. Multiples of 1 kHz represent the harmonic distortion. Due to the perfect symmetry of the circuit, the even multiples cancel out (for example, 2 kHz) and you only see a tiny THD peak at 3 kHz, which is below 90 dB and therefore inaudible!
The noise increases significantly at low frequencies due to the RIAA (standarised equalization filter for record playback). Peaks at 50 Hz, 100 Hz ... are the familiar hum (for countries with 60 Hz AC power frequency it would be 60 Hz, 120 Hz...), the rest is a rather dark sounding noise.
Such a large difference as shown is dramatic and the noise, as well as hum of the phono preamplifier is thus, in relation to the groove noise, absolutely irrelevant.
This is the fulfillment of a long-cherished dream of MC cartridge users, through better technology!

 

Amplifier Circuit

1. Balanced Current Injection input.

2. Common base circuit for highest bandwidth.

3. "Automatic" gain adjustment.

4. Feedback-free circuit with very short signal path.

5. Fully balanced circuit.

6. Balanced LEF single-ended Class-A output.

 

The Current Injection Circuit

The Current Injection input circuit is a remarkable implementation of the principle of the common-base circuit. It is known for having the widest broadband, the least distortion, the best dynamics, and the most musical sound of the three baic transistor circuits by not making a copy of the input signal. CI is rather more like an I/V converter than an amplifier in the traditional sense.
The original current of a MC cartridge gets "injected" into a balanced static system of currents, and the first amplified signal is made from the original current, virtually lossless. This way the MCCI Signature ULN turns the weakest point of a phono MC amplifier into a very low loss processing stage. Dynamic losses and distortions are remarkably lower compared to common voltage amplifiers.
Beside this remarkable advantage the first RIAA pole is done by making this I/V conversion stage frequency dependet and thus combining the advantage of a passive RIAA without the need of excess gain.
The MCCI Signature ULN has a low-impedance input. Fortunately, the circuit is a perfect match for MC pick-ups and D/A converters, our best audiophile sources. For decades, some of the best MC amplifiers in the world have used the common-base circuit. However, only balanced input independent from the electrical ground allow the MC cartridge to be coupled directly with a common-base circuit without risk or comprises. The Current Injection circuit, compared with traditional circuits, significantly reduces dynamic loss, and signal distortion and discoloration.

LEF Output Stage

Because the Current Injection circuit has a high-impedance output, a stable buffer is required to drive the load. Seen dynamically, there is no alternative to single-ended amplifiers, which run in Class-A drive. In a Load-Effect Free drive, the single-ended Class-A transistor, which is decisive for the sound, is freed from the work of driving the load. This is why we say it is Load-Effect Free. The quality goes through the natural lack of distortion up and above the classical Class-A mode, and therefore eliminate the need for negative feedback.

Truly Balanced Circuit

In balanced Class-A mode, the supply voltage is not modulated through the music signal. One must keep Phono in mind. The output of a phono-amplifier produces a few volts at high levels, but the input has a sensitivity in the μVolt area. The balanced Class-A mode leads to a distinct increase in the inner tranquillity of the sound pattern, leaving more room for fine details, dynamic leaps, relaxation of the performance, and three-dimensional spatial illustration. In other words, an intense, in-depth music listening experience.

RIAA Equalization and Adjustment Options:

1. Three selectable gain levels.

2. Neumann-corrected RIAA or traditional RIAA.

3. Selectable subsonic filter.

4. RIAA options for low-end extension and warmth.

5. Virtually lossless passive equalization within the I/V converter.

Because all B.M.C. analog circuits work without negative feedback, there is no "active" equalization for the RIAA specification. For a precise RIAA correction, the equalization takes place in a passive manner in two stages uncoupled from each other, which calls for a frequency-dependent current/voltage converter. The B.M.C. MCCI Signature ULN combines the neutrality of passive filtering with the avoidance of unnecessary amplification.

The classic RIAA equalization is wrong because when doing the master-cutting EQ there is no endless rise in the high frequencies as they are corrected. Correction takes place In the MCCI Signature ULN with the help of the quasi industrial standard of disk-cutting lathes by the Georg Neumann company. LP playback following this standard simply possesses more air and openness. One can deactivate the Neumann correction and easily hear its advantages.

It is even possible to slightly raise the lowest deep bass as well as the "warmness" level to correct recording errors or slightly bass-poor pick-up/pick-up arm combinations.

Ideally the cartridge should match to the tonearm and the system should be well damped. In other cases a soft subsonic-filter can be selected.

Although the gain between different cartridges differs less than usual, according to the construction of the MC there might be level differences. The MCCI Signature ULN allows the setting of 4 different gain levels.

Components of the Highest Value

1. Special ultra-low-noise transistors with very high Hfe, ten in parallel.

2. Balanced Current capacitors for precise and colorful sound.

3. Induction-free polystyrene capacitors.

4. Metal thin-film resistors with 0.5% tolerance.

5. Fully gold-plated four-layer printed circuit board.

6. Copper-plated iron shield cover with effective vibration damping.

7. Massive aluminum chassis with resonance damping.

8. Extremely clean and silent power supply.

MCCI Signature ULN'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 built 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.

Time for 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 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 over the whole frequency range for really unveiling the advantages of Vinyl-reproduction. Part of this philosophy is the abandonment of global feedback for RIAA and other amplifiers. Then music can blossom and capture our emotions while being relaxing; leading us into a different world, touching and possibly even seducing us...

 

The Sound of Nature