RSA-BW7 EX IS THE LATEST AMPLIFIER from SPEC CORPORATION. It’s also one of the smallest in their catalog. It is 350 mm wide, 95 mm high and 375 mm deep, yet it offers 100 W (4 Ω). It weighs a moderate 7 kg, because there are no heavy heat sinks in it, and instead of a linear power supply for the entire device, we find a small power supply of this type for the volume control circuit and a switching power supply for the power amplifier.
SPEC CORPORATION amplifiers have a very balanced, very Japanese look. The combination of metal and wood immediately catches the eye. We haven’t talked about it yet, but SPEC encloses their amp cabinets with wood. This is explained by the fact that devices operating in class D, i.e. with high switching frequencies, are very sensitive to vibrations.
And one of the best methods to suppress them is the use of wood. SPEC says that in choosing a particular material, it follows the steps of luthiers building musical instruments. Such a “package” consists of several elements – in this case three: two side walls, which also form the front feet, and a third foot at the back of the device. Each model is carefully auditioned to select the best type of wood for these elements. Metal elements are made of steel and aluminum (front).
It is minimalist amplifier – which again refers us to tube devices because it only offers volume control and input selection. And there are only four of them, all linear: three RCA and one XLR. The device is an unbalanced design, so the latter is added for the convenience of the user but not truly symmetrical. The only two LEDs indicate the status of the device – the white one means it’s on and the red one means it’s turned off. The power supply is turned on using a great, characteristic for this company, toggle switch with a latch, preventing accidental switching off.
The signal from the nice, gold-plated, screwed-on input sockets runs via long Belden interconnects to the switch on the front panel, and from there returns to the amplifier board. At its input there is an integrated Cirrus Logic 3310-KSZ resistor attenuator. It is an analog resistor ladder, no longer produced, but SPEC still values it. However, there is another chip next to it, Tachyonix Corporation – and its symbol is 3310IR01. This encoder is manufactured by this Japanese company under the license of the International Rectifier, and is based on the 3310S06S model. It cooperates with the knob on the front panel and converts its position into a series of signals controlling the attenuator.
After attenuation, the signal goes to the modulator, which together with the MOSFET output transistors is placed on the bottom of the board; transistors were screwed to the bottom of the case, which acted as a heat sink. Voltage stabilizing circuits are screwed to the side of the chassis by means of an aluminum bar.
The output of the amplifier is a key element of the circuit – it is a reconstruction filter. It is made of coils and capacitors. These are core coils. SPEC has been experimenting with capacitors for years. Instead of one, they selects several of different built, checking the sound during listening sessions. In the tested amplifier, there are three different types of capacitors at the output of each channel, and the manufacturer says that these specific capacitors are responsible for excellent bass:
• electrolytic, by Nichicon,
• mica, manufactured for SPEC, belonging to the MC-DA series. They are made of laminates, which is supposed to reduce inductance, and the material which is the best mica of this type, “ruby mica”, comes from India. The electrodes are made of sputtered silver,
• polypropylene from Vishay.
Maximum output | 100 W × 2 (4Ω), 75 W × 2 (6Ω), 50 W × 2 (8Ω) | |
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Frequency response | 10 Hz – 30 kHz ±1dB (6Ω, 1W) | |
Harmonic distortion ratio | 0.02% (at 1 kHz, 80% output) | |
Input sensitivity, gain | 300 mVrms, 37.3 dB (at MAX volume, 6Ω, 1kHz, unbalanced input) | |
Line input terminals | XLR input : 1 RCA inputs : 3 | |
Speaker terminal | 1 | |
Power supply, other | ||
Power voltage | 220V AC,50Hz | |
Electrical consumption | With no signal : 18 W, during maximum output : 180 W (8 Ω, 100 Hz) | |
External dimensions | 350 mm (width) × 95 mm (height) × 375 mm (depth) | |
Weight | 7.0 kg |