UESUGI U / BROS-25

Commentary

A tweeter system that combines a power amplifier and an electronic crossover network in addition to a dedicated tweeter.

The electronic crossover network is a two stage CR-type filter with a good connection between the low-frequency and high-frequency sides.
Since the signal output on the low frequency side is high impedance, a cathode follower feed amplifier using a vacuum tube is installed to prevent external noise including hum components from entering.

All the amplifiers are vacuum tube type, and all the vacuum tubes used are select tubes manufactured in the heyday of vacuum tubes.
The 6L6GC power tube is made by GE Corporation of the United States, and the 6189 driver tube (highly reliable 12AU7/ECC82 tube) is supplied to the United States Army.

The first stage of the power amplifier section is ECC83/12AX7, and the driver and phase inverter stage is a 6189 type cathode coupling type. By directly coupling the first stage with the driver and phase inverter stage, the time constant in the low frequency range is eliminated and excellent low frequency transient characteristics are obtained.
The power stage is a 6L6GC self-bias system ultra linear connection push-pull system designed to provide stable operation over a long period of time.

The tweeter section of the U ・ BROS-25 has an impedance of 8 Ω. However, considering the case where the U ・ BROS-25 is set to the full range and a full-range speaker is connected, the output matching impedance is set to 4 Ω and 16 Ω in addition to 8 Ω.

As with other Uesugi amplifiers, we use transformers jointly developed with tamura Manufacturing.
The output transformer is designed with excellent phase characteristics, and the negative feed back is connected to the cathode of the first stage from the exclusive winding, so the operation is stable.
The power transformer is completely sealed with a short ring and a ham proof belt to prevent leakage flux.

As for the chassis, after bending a 1.6 mm thick high-grade steel plate, solder is poured into all the welded parts and polished to create the rounded corners of the four corners.
The bonnet cover is also treated in the same way.

In consideration of the unique noise generated when a printed circuit board is used, no printed circuit board is used for the wiring, and the wiring is done manually by veteran craftsmen.

The tweeter section is equipped with a 3 cm soft dome type tweeter made by Dinavio.
This unit has excellent directional characteristics, similar response curves for on-axis 0 °, 30 °, and 60 ° characteristics, excellent distortion factor characteristics, and wide range.
Although a cabinet is not required for operation, it is contained in a special cabinet for stable setting. This cabinet is designed for high mechanical strength and uses solid walnut as a surface treatment material.
The front net can be attached and removed, but tuning is done with net.

To connect the U ・ BROS-25, first connect the output signal from the preamplifier to the input of the amplifier section of the U ・ BROS-25 using a pin cord, and then connect the low-frequency output signal of the U ・ BROS-25 to the input of the power amplifier using a pin cord and to the main speaker.
The tweeter section of the U ・ BROS-25 is connected to the 8 Ω output terminal of the amplifier section with a speaker cable.

The amplifier section of the U ・ BROS-25 is equipped with a frequency range selector. In normal use, the high position provides a low-cut output signal.
When this position is set to the full position, it outputs the whole band like a general power amplifier, so if you connect the tweeter section of the U ・ BROS-25, it will be damaged.

If you are using a power amp, set the level control to the maximum value, and adjust the volume with the U ・ BROS-25 level control.
If the high range is insufficient even if the U ・ BROS-25 level control is set to the maximum value, set the U ・ BROS-25 level control to the maximum value and adjust the power amp level control.

Model Rating

Type	Tweeter system
Amplifier Unit
Crossover frequency	2.5kHz
Slope characteristic	-12dB/oct
Input sensitivity	560mV
Input impedance	About 70k Ω
Low-pass signal output impedance	About 600 Ω
Rated output	25W + 25W (continuous output)
Output impedance of power amplifier section	4 Ω, 8 Ω, 16 Ω
Distortion factor	Not more than 0.1%
Damping factor	About 10
Residual noise	0.2 mV or Less (8 Ω)
Vacuum tube used	6L6GC : 4 pcs (Rice / GE) 6189W : 2 units (US / JAN) ECC83/12AX7 : 2 (West Germany / Siemens)
Power consumption	Approx. 150W
External dimensions	Width 320x Height 199x Depth 337
Weight	Approx. 16 kg
<Tweeter Part>
Units Used	For High Range : 3 cm Dome Type (manufactured by Danudio)
Impedance	8 Ω (5 kHz)
Frequency characteristic	2.5 kHz to 45 kHz
Output sound pressure level	90dB/W/m
External dimensions	Width 305x Height 196x Depth 175 mm
Weight	Approx. 4 kg