Hitachi SR-903


Hitachi SR-903

Sou fã da Hitachi, esta marca fez bons aparelhos, e este é um excelente exemplar.

Quando se ouve falar da Hitachi, não se associa esta marca ao material áudio criado capaz de competir com grandes nomes do áudio vintage como a Sansui, Pioneer, Kenwood ou Marantz.
Mas, é quando se analisam os rádios da Hitachi, especialmente os topo de gama irmãos gémeos  SR 903/904, que se perceber porquê.
Falo aqui do Hitachi SR-903 de 1977, praticamente igual ao 904, que é uma pequena actualização cosmética do 903, com a adição de medidores VU.
Os medidores VU são fixes, mas gosto mais do estilo anos 70 do 903 e dos botões de alumínio...

Estes aparelhos são grandes, bem construídos, som detalhado, graves limpos e dinâmicos, bem controlados, umas bestas de som.
Todas os componentes foram fabricados pela Hitachi, excepto os condensadores. Transformador maciço e um número excepcional de transístores.

O amplificador utiliza a tecnologia Hitachi Classe-G, de 3 vias que permite oscilações de tensão adicionais e aumentar a potência de pico em certas frequências, outras marcas na altura tentam utilizá-la, mas a Hitachi soube como fazê-lo correctamente. Estável e com um som potente. E é por isso que lá está a designação "Dyanharmony"!
A potência de saída do SR-903 é de 75 watts por canal RMS. No entanto, durante os picos de som, a potência pode chegar aos 160 watts por RMS de canal para evitar o corte e a distorção. Boa!

Citando a revista StereoMagazine:
"Pode produzir um pouco mais de 3 dB acima da potência nominal - ou seja, o dobro da sua potência contínua em picos transitórios sem clipagem, rivalizando neste caso com a performance em muitos super amplificadores. ... o desempenho excede de longe o que se pode esperar de um amplificador convencional de 75 watts. A potencia generosa contribui para uma sensação clareza e nitidez".


















Especificações Técnicas:

Audio Section
Min. RMS Continuous Power Output (both channel driven):
75 W +75 W (8 Ω, 20-20,000 Hz, THD 0,1%)
95 W + 95W (8 Ω, 1 kHz, THD 0,1%)
105 W + 105 W (4 Ω, 1khz, THD 0,1%)
Music Power (IHF): 160 W + 160 W per channel into 8 ohms
Power bandwidth: 10 Hz - 50 kHz
Frequency Characteristics: 10 Hz - 30 kHz ±1 db
Total Harmonic Distortion:
At rated output : less than 0,1%
At ½ rated output: Less than 0,03%
Intermodulation Distortion:
At rated output : 0,1%
At ½ rated output: 0,03%
Input Sensitivity/Impedance:
Phono : 1,9 mV/47 k Ω
Aux : 150 mV/50 k Ω
Tape 1, 2 : 150 mV/50 k Ω
Adaptor : 150 mV/50 k Ω
DIN : 400 mV/120 k Ω
Output level
Tape Out :
150 mV : phono, Aux at rated input;
200 mV : FM 400 Hz, 30% dev. Input; 1 mV;
150 mV : AM 400 Hz, 30% mod. Input ; 1mV
DIN Out : 40 mV (phono at rated input)
Signal-to-Noise Ratio (IHF, Input shorted, A-network, rated power):
Phono : 75 dB
Aux : 87 dB
Tape : 87 dB
Damping Factor: 45 (1 kHz, 8 Ω)
Equalizer: RIAA ±0,5 dB
Bass Control: ±10 dB at 100 Hz
Midrange Control: ±6 dB at 1 kHz
Treble Control: ±10 dB at 10 kHz
Loudness Control: +9 dB at 100 Hz ; +4 dB at 10 kHz
High Filter: -8 dB at 10 kHz
Low Filter: -8 dB at 50 Hz
Semiconductors: 5 Ics; 1 FET; 57 Transistors; 62 Diodes; 1 Thyristor
FM Section
Frequency Range: 88 - 108 MHz
Usable Sensitivity (IHF): 9,3 dBf (1,6 µV)
Signal-to-Noise Ratio [Mono/Stereo]: 74 dB / 68 dB
Total Harmonic Distortion [Mono/Stereo]:
At 100 Hz : 0,2% / 0,3%
At 1 kHz : 0,15% / 0,25%
At 6 kHz : 0,25% / 0,3%
Frequency Response: 30 Hz - 15 kHz ±1 dB
Image Response Ratio: 85 dB
Spurious Response Ratio: 100 dB
IF Response Ratio: 100 db
Altenate Channel Selectivity: 80 dB
Capture Ratio: 1 dB
AM Suppression: 55 dB
Stereo Separation: 45 dB
Sub-Carrier Suppression: 65 dB
SCA Rejection: 65 dB
Muting Threshold: 14 µV
Antenna Input:
Balanced : 300 ohms
Unbalanced : 75 ohms
AM Section
Frequency Range: 530 - 1,605 kHz
Sensitivity: 300 µV/m (S/N 20 dB); 20 µV (IHF, ext. Antenna)
Image Rejection: 70 dB
IF Rejection: 90 dB
Selectivity (IHF): 40 dB
Signal-to-Noise Ratio: 50 dB
Antenna: Ferrite and separate terminal
Tape Monitor: 1,2
Speaker Switch: A, B, A + B
Speaker terminal: One-touch terminal
Power Supply: 100/120/220/240 V 50/60 Hz
Power Consumption: 615 W at 4 Ω; 430 W at 8 Ω
Dimensions (W x H x D): 490 x 144 x 400 mm
Weight: 13,5 kg (29,8 lbs)

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