Aurex SC - Λ 99

Commentary

This is a stereo power amplifier that pursues sound quality in all aspects such as Λ power supply, Λ loop, chassis structure, parts and internal layout.

Pure class A operation and class AB operation can be selected for SC-Λ 99 by switching the switch.
In pure class A operation, there is no degradation of sound quality because the distortion is not avoided by varying the bias as in a pseudo class A amplifier. Moreover, the best characteristics of the element can be drawn out because the bias point is placed at the best point of the amplifying element.
In class AB operation, the super f_TThe use of power transistors and low-distortion circuits reduces switching distortion to an undetectable level.

The circuit configuration is a fully symmetrical type with dual FET differential cascode connection, three stage Darlington connection, and triple parallel output stage. The power transistor is a super f of Pc150W._TBy using a power transistor, we can obtain an allowable input with a margin, and by keeping the capacity and number of high-frequency phase correction capacitors small, we have succeeded in obtaining stable gain up to the high-frequency range.
One chip low-noise dual FETs (2SK90A-Nch, 2SJ90A-Pch) with excellent thermal balance are used in a fully symmetrical form. The input stage to the output stage are operated symmetrically to reduce the distortion factor. In addition, in order to ensure stable operation up to the ultra-high frequency range, all the amplification stages are configured as two stage amplification circuits by cascode connection. This improves the SN ratio by 7 to 8 dB compared to the conventional one. 270

When the speaker is driven, the diaphragm moves and a back electromotive force flows into the amplifier and distorts the speaker input signal. The SC-Λ 99 has a high damping factor of 500 and low output impedance, reducing the influence of the back electromotive force of the speaker.

Uses Aurex's unique super Λ power supply.
In class A operation, the collector output impedance of the power stage, driver stage and pre-driver stage becomes small, so that the influence of the impedance of the power supply part appears. In SC-Λ 99, the super Λ power source adopted in SY-Λ 88II is developed to promote low impedance between AC power source and amplifier, and is adopted in the power supply part up to the pre-driver stage. This realizes ultra-low impedance and low noise of only 0.5m Ω from DC to 100 kHz.

The central part of the super Λ power supply section is simplified by using one stage differential, and the power supply section is provided with sufficient space by using parallel control power transistors.
In addition, two large and small transformers, a large power toroidal transformer and a driver toroidal transformer, are installed to further improve sound quality.

In order to achieve low impedance, the power switch is of large capacity, and rectifiers, newly developed electrolytic capacitors and various film capacitors are used in parallel.
Newly developed large-scale electrolytic capacitors for power supply are used. They are equipped with 18,000 μ F/80Vx4, 1.000 μ F/80Vx4, 820 μ F/80Vx8, and 560 μ F/100Vx4. In addition to low impedance, we are also working to reduce contact with dissimilar metals and prevent vibration. Solid capacitors for signal and power supply systems include copper foil styrene capacitors, u Λ -II type Λ capacitors, and copper foil film capacitors. In particular, film capacitors are manufactured by a special manufacturing method to suppress resonance over a wide range and realize high sound quality with little distortion. Electrolytic capacitors are also manufactured by a special manufacturing method based on consideration of film capacitors, and achieve an excellent energy balance.

A high-purity oxygen-free copper 280 μ m thick glass epoxy board is used for all printed circuit boards except for the indicator part. This reduces vibration by increasing the weight of the board while achieving low impedance.

As the emitter resistor of the output stage, a Λ loop including a Λ resistor using copper as a resistor is adopted, so that all the paths for large current flow are unified with elements using copper.

Two large extruded aluminum heat sinks are attached to the heat pipe that uses the heat of vaporization. This heat pipe achieves a high heat radiation effect. In addition, the power transistor in a sandwich structure made of a large aluminum material and a 2 mm thick copper plate. This prevents thermal imbalance in the power transistor and reduces the noise of the transistor as well as a high heat radiation effect.

Aluminum is used for the chassis.

In addition to the DC voltage detection type, the protection circuit adopts a double protection circuit equipped with an abnormal temperature detection of the heat sink.

A 15A AC cord has a polarity indicator to adjust the polarity of the power supply between devices.

Model Rating

Type	Stereo power amplifier
Rated Output (20 Hz ~ 20 kHz)	Class A : 50W + 50W (8 Ω) Class AB : 200W + 200W (8 Ω)
Total harmonic distortion rate (20 Hz to 20 kHz)	Class A : 0.0028% (at rated output) 0.0025% (at 1/2 output) Class AB : 0.003% (at rated output) 0.0028% (at 1/2 output)
Intermodulation distortion factor (50 hz : 7 khz = 4 : 1)	Class A : 0.0028% (at rated output) 0.0025% (at 1/2 output) Class AB : 0.003% (at rated output) 0.0028% (at 1/2 output)
Frequency characteristic	DC ~ 500 khz + 0 -1.5 db
Output Bandwidth (8 ω, -3dB)	Class A : 5 Hz to 100 kHz (0.005% distortion) Class AB : 5 Hz to 100 kHz (0.01% distortion)
Input Sensitivity / Impedance	Class A : 0.67V/50k Ω Class AB : 1.34V/50k Ω
Residual noise (input short)	70 μ V (8 Ω)
Signal-to-noise ratio (IHF, A-network)	-128dB (input conversion)
Damping factor	500 (1 kHz, 8 Ω)
Speaker impedance	4 Ω ~ 16 Ω
Power supply voltage	100 VAC, 50Hz/60Hz
Power consumption	370W
External dimensions	Width 450x Height 172x Depth 473 mm
Weight	30kg