Hitachi SR-903

Hitachi SR-903

Well… I like Hitachi, I think they made great stuff, and this, is one excellent receiver.

When you ear Hitachi you don't think that this company had created audio stuff that could compete with big names in vintage audio like Sansui, Pioneer, Kenwood or Marantz.

You have to check Hitachi receivers, specially the TOTL twin brothers SR 903/904 to understand why.

This is the 1977 Hitachi SR-903, the 904 was a small cosmetically update to the 903 and addition of VU meters.

VU meters are cool, but I like more the 70s look of the 903 and the aluminum knobs…

They are big, well-built, crispy in details, clean and dynamic, well controlled bass, a sound beast.

All the parts inside of them where manufactured by Hitachi except the filter caps. Massive transformer and an outstanding number of transistors.

This receiver uses the Hitachi Class-G topology, it has a 3 rail which allows additional voltage swings and increase peak power output at certain frequencies, other brands at the time try to use it, but Hitachi know how to do it right and this receiver is one stable beast that sounds great. And that is why there is a "Dyanharmony" badge!

The power output stage of the SR-903 is rated at 75 watts per channel RMS. However, during musical peaks, the high output stage automatically produces 160 watts per channel RMS to prevent clipping and distortion. Nice!

StereoMagazine sayd:

"It can produce a little more than 3 dB above rated power - that is, twice its continuous wattage rating on transient peaks without clipping, rivaling in this case the performance on many a superamp. … performance far exceeds what can be rightfully expected of a conventional 75 watts amplifier. The generous headroom contributes to a sense of ease, clarity and crispness."

Specifications

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)