BAlabo – BC-1 MK-II Control Amplifier from Bridge Audio Laboratory
The BAlabo BC-1 MK-II control amplifier (aka linestage) sports a radical new design concept in preamplification. With power supply voltage secondaries running internal components at an amazing 120 volts, the BAlabo BC-1 MK-II offers explosive musical peaks, unbelievably nuanced micro dynamics and a silky smooth top end. At first listening, the BC-1 MK-II offers a sense of complete control and rightness of dynamic presentation – both aspects, immediately evident. Further listening reveals a level of transparency and liquidity that is virtually unknown in all but the finest tube components with one important difference – the BAlabo BC-1 MK-II is a 100% solid state design. As a result, soundstaging is incomparable and at minus 110 dB, its noise is essentially non-existent.

Improvement of Low Level Linearity by Post Attenuation Scheme
A typical preamplifier circuit uses the pre-attenuation method - input signals are attenuated at the first stage of an amplifier, before the signal is amplified. This method, however, degrades sound quality, since low-level signals, once attenuated, are lost in the thermal noise and fluctuations of small, board-level components. No matter how excellent an amplifier is, the original signal can never be restored once it has been attenuated at low levels.

The BC-1 uses a “Post Attenuation” scheme to avoid signal degradation – particularly low level signals and corresponding microdynamics. Line level signals are amplified at the input stage of BC-1 prior to reaching the volume control. The high voltage power supply of the BC-1 facilitates this method and preserves dynamic range and low-level linearity. The result is nothing short of stunning. Even experienced listeners express disbelief at first.

58 Position Volume Attenuator
The BC-1 control amplifier uses a volume control with a highly reliable switch that consists of 8 circuits with 58 positions - accurate to 0.2 dB at every position. All resistors are custom made by an experienced manufacturer with a long history of providing superior quality components to the audio industry.  In addition, copper plates are installed between each section of the volume control for shielding and absorbing acoustical vibration – sometimes associated with electrical contact vibration and always resulting in deterioration of audio quality. The switch assembly itself employs anti-vibration material in conjunction with copper plates to avoid the possibility of any mechanical resonance. The switch is mounted to the chassis of with additional vibration isolation to offer complete immunity from external vibration.

Low Impedance Power Supply by w/ 3D Construction
In a typical control preamplifier, the power supply feeds necessary voltages to multiple points in the circuit. Therefore it is impossible to arrange a single sensing point for feedback to the voltage regulator.  A feedback type voltage regulator can reduce its internal impedance by reversing additional energy.  Even though reversed energy is correctly generated at the sensing point, the reversed energy has a negative effect on the PCB board which is electrically separate from the sensing point since the impedance of the copper trace's is not true "zero" even though it is only a few millimeters in length. The BC-1 doesn't try to lower the impedance of the reversed energy, but the three-dimensional structure acts to decrease the effective impedance by arranging the specially designed capacitors in close proximity to the actual electric current load point in order to supply instantaneous power.  In other words, the separate PCB with BY-PASS capacitors joins the amplifier PCB to achieve the shortest distance in each section of the amplifier by using a three-dimensional wiring scheme.

Moreover, the circuit board is set up as a shield layer. Since it is designed compactly, the supply loop is minimized in length for ultra-low impedance. The BC-1 can therefore realize superior impulse response and stability over an extremely wide frequency range.

Precision Balanced Amplification
The BC-1 employs six blocks of amplifiers in each channel, in a perfect balanced circuit with high S/N and high input/low output impedance.  The amplifier’s first stage works as a buffer amplifier that utilizes a combination of a DIAMOND CIRCUITRY and FET source followers. The second stage is a differential amplifier with current feedback.  The third stage uses the same design construction as the first stage.  Since signal imbalance between plus and minus polarity in a balanced circuit degrades THD, every BC-1 is carefully tuned at the factory with hand-matched feedback resistors, that perfectly reject common mode noise and drive THD to an absolute minimum.

Mechanical Grounding of Chassis
The four corners of the chassis are constructed with heavy-duty, extruded aluminum for superior mechanical integrity. The chassis is designed to aid in the dispersion of the resonant frequencies by the use of various materials (Aluminum/Steel/Corian) each with their own properties of absorption and transmission. External vibration is never propagated to the internals of the amplifier. Vibration attenuation is achieved with the use of CORIAN® resin (high tech thermo-plastic material which is hardened by the powder of oxidized aluminum) which is located along the top and bottom edges lengthwise so that side wall,  top cover and the bottom plate are all dampened. As the result, the local resonance of each structural member is suppressed to an absolute minimum.

Noise Reduction for AC Line and Power Rectification
In home environments, electronic equipment like personal computers, add noise to the power mains and degrade the AC waveform - this can deteriorate the performance high quality audio components.  The BC-1 employs a power line filter that is a ‘closed type’ at the location of the AC inlet. The filter cuts the external noise and reshapes the AC wave form.  The transformer of BC-1 has a very advanced shielding scheme when compared to most conventional transformers with toroidal cores.  Most toroids have difficulty in creating a true ‘static shield’ using conventional construction methods.

The BC-1 MK-II has adapted an insulating copper foil to act as a shield between the primary and secondary windings – and the chassis – completely shielding the transformer and eliminating electromagnetic couplings. Rectification noise is also reduced with a BYPASS capacitor that is carefully selected for quality sound.  The rectifying diode is a high-speed type, selected for its very low noise. Off the shelf capacitors after the rectification stage can have a negative influence on audio quality.  Therefore the BC-1MKII uses custom-made capacitors developed specifically for this application. Radiation noise generated by leakage flux from charging current flow in the capacitor is prevented by means of three dividing shield blocks made of aluminum with a floating mechanical support that shunts vibration away from the transformer. The result is an astonishing 20dB mechanical noise suppression at the transformer.

Signal Switching by Relay
For switching audio signals, relays are used to optimize the internal construction and improve operational feel. These relays are custom made and have gold plated contacts with a mirror surface finish to prevent signal degradation from oxidized or pitted surfaces.  The L/R balance adjustment circuit has an eleven-step resistance changeover enabled by relays.  Thus, any signal deterioration by use of the channel balance circuit is negligible.

Stand-by Function
A stand-by switch is located on the front panel so the BC-1 is ready at all times to provide the optimal sound quality without the need for a warm up period. Electrolytic caps remain charged during standby. Main on/off is located on the rear of the chassis.

Remote Power On/Off for Amplifiers
The remote power on/off scheme is employed in all BAlabo products.  The BC-1 has a pair of RJ11 jacks on the rear panel for use with external equipment such as power amplifiers, for the remote control power on/off of those units. This system is completely isolated from the audio signals.

PowerKon AC Inlet
The AC inlet connection is very important for proper operation. The BC-1 uses PowerKon connector made by Neutrik Corporation of Germany. The PowerKon inlet for the AC mains offers superior reliability and product safety.  The PowerKon has one-third the contact resistance of conventional connectors and a larger maximum current rating (20A). The PowerKon is a bayonet, snap-in mechanism and is designed to prevent unexpected disengagement of the AC cord.

Integrated Spikes for Rigid Installation
The feet of the BC-1 are coated with Teflon with an under cushion material to prevent shipping damage. Once the BC-1 is installed, spikes (included) can be threaded into the base of each foot for additional mechanical grounding.

Custom Components Throughout
For the ultimate in sound quality, components must be selected through careful listening tests. The BC-1 uses many custom components, such as all electrolytic capacitors in the power supply section, fixed resistors for the audio signal, copper foil capacitors for phase compensation and the relays. As a result of these selections, audio improvements are easily heard when compared to bulk style, off the shelf components.