Integrated Amplifier

PREMIUM SILVER / PREMIUM BLACK

Every SOULNOTE technique has been lavishly incorporated into the current culmination of our perfectly balanced non-NFB technology. This integrated amplifier is loaded with a variety of monaural drive and power amplifier modes, like the new BTL/bi-amp setting.

Perfectly balanced, discrete non-NFB circuit

SOULNOTE's original perfectly balanced non-NFB circuits have been fully optimized and incorporated to give sound quality the highest priority. Voltage feedback has been completely eliminated in the output stage, the voltage amplification stage, and the power supply circuits. Because of their impact on the sound, circuits of DC servo and current mirror have been eliminated, while both the constant current and bias circuits in the voltage amplification stage employ simple circuitry layouts that only use constant current and voltage elements (2SK209 and LEDs, respectively) carefully selected for utmost sound quality. The voltage amplification stage is perfectly balanced all the way through the emitter follower output. A-2 is designed to reproduce music in a dynamic, open, clear, and soulful way.

Relay-switching balanced attenuator

The volume adjustment is not controlled by electronics or a rotary-type slider volume, but instead incorporates SOULNOTE's original relays in a balanced attenuator system that switches high-precision resistors. This dramatically increases clarity and allows the sound image to emerge in three dimensions. It also significantly improves quality in a low volume level without worrying about gang errors.

An ideal construction

The input signal line has been minimized by concentrating the input terminals, input selectors, volume, and the non-NFB voltage amplification stage onto a single multi-layered board. The board does not use even a single shield or filter that could negatively impact the sound in order to eliminate every factor that reduces sound quality, such as the effects of vibration from connecting cables, inductance components, radiation noise, etc. This ideal construction has been achieved thanks to the relay-switching balanced attenuator.

4-layer board with 70μ thick copper foil

Composed of the output stage and the main power supply, the power block features an inner layer of 70μ thick copper foil substrate inner layer plane as the power supply busbar and thus minimizes high current loops in the commutating capacitor > output transistor > loudspeakers + terminals > loudspeaker terminals > commutating capacitor cycle. Eliminating inductance components in high current lines creates outstanding frequency characteristics and stability.

Direct connection

Connectors have been eliminated in the power supply as well as the signal lines, and cables are instead soldered directly to the boards for direct connections.

Chimney-type heat sink

The heat sink is a newly developed chimney type that pursues a shape with high cooling efficiency and low intrinsic vibration.

Powerful power supply

The power supply utilizes a 600 VA bifilar wound toroidal transformer, the most powerful in SOULNOTE's history. Commutating current loops have been minimized by placing ± independent rectifying circuits from the fast recovery diode close to the transformer winding. The commutating capacitor is supplied by ELNA specially developed for SOULNOTE and selected for its sound quality. Connecting multiple capacitors of small size in parallel helps adjust and optimize high frequency characteristics and overall capacitance.

4 parallel high-speed output transistors

The final stage is composed of 4 high-speed transistors (2SC2837/2SA1186) with low Cob and high FT connected in parallel. This combines with the strong non-NFB power supply to provide generous loudspeaker driving power.

Output transistor selection

The output transistors have been selected and paired by using a specially designed device that measures the Vbe current value while avoiding any influence from rising temperatures in the output transistors. Perfectly aligning the 4 parallel current transistors creates abundant loudspeaker driving power and clear, precise sonic reproduction.

4-step Darlington circuit

High-frequency transistors create a 4-step Darlington configuration to drive the final transistors completely, thereby optimizing the amount of each current. This produces plentiful drive power for every loudspeaker.

Housing design that prioritizes sound quality

A spike grounds the power supply transformer directly, and while combining the spikes with uneven cross-sectional aluminium panels to control resonance has increased rigidity, the aluminum panels are not directly bonded in order to eliminate unwanted resonance. The top cover, which has a particularly large influence on sound quality, features a dual-component construction that joins the base plate and the aluminum panels at three points so that they do not dampen each other. By grounding it at three points without fixing it to the aluminum portions of the housing itself, this design succeeds in keeping the balance of sound while still keeping it expansive.

Single non-NFB differential BTL circuit

The conventional BTL monaural principle that uses the left and right channels of the stereo amplifier in reverse phases can produce powerful sound quality, but the sound impression tends to blur with sounds tending to clump together because of the effects from GND lines or matching two amplifiers. The BTL monaural mode in the A-2, therefore, adopts a new approach that partitions the differential output of one non-NFB differential amplifier each for the left and right final stage. This creates an expansive sound with vigorous, yet delicate BTL driving.

Two types of monaural modes

In addition to BTL monaural mode, the bi-amp monaural mode can also be selected to distribute the monaural input to the left and right channels.

Power amplifier mode

The power amp mode interrupts the power supply to the microcomputer and bypasses the selector and volume. This increases the SN ratio. XLR and RCA input can also be selected in this mode.

Select from six possible use cases

• Stereo pre-main amplifier
• BTL monaural pre-main amplifier
• Bi-amp monaural pre-main amplifier
• Stereo power amplifier
• BTL monaural power amplifier
• Bi-amp monaural power amplifier