Hitachi SR-903

 Hitachi Class G Stereo Receiver SR-903 (1977)

The SR-903 is a great match for power-hungry speaker systems. The low power output stage of the SR-903 delivers 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.

The SR-903's other outstanding features include:

Dual Gate MOS FET for high quality FM tuner

Auto-lock AFC circuit

High selectivity and low disstortion IF amplifier using ICs and 3 ceramic filters

Quadrature detection

Phase lock loop circuitry for FM/MPX circuit

A ceramic filter, IC in AM Tuner

Two large easy-to-read meters,

Large-sized flywheel tuning knob,

A newly developed high efficiency high power audio amplifier (named series E Amplifier)

Nwe IC in the equalizer,

Mid-range/treble tone controls,

Electronic  protection circuit,

Hi and low filters,

Tape dubbing,

Two speaker syatems connection,

Detent controls.

 Only Hitachi SR-903 has Class G, the very newst class in amplifier operation.

Stereo review went on to explain that this exclusive circuitry " uses a low power and a high power output stage operating together.. At low signal levels the lower power stage drives the speakers. The transition to the more powerful output transistors .. Takes place smoothly at the point where it, becomes advantageous to do so."

The point they're talking about, of course, is where certain portions of the music you listen to demand more than the rated output to sound like they should.  So when your music really gets thrilling, Class G cuts into a standby amplifier. Then, for just a moment, the SR-903 can pump out a lusty 160 watts per channel - without clipping.

As a wrap-up. Stereo review said Class G delivers "much higher overall efficiency than a conventional device, and this brings immediate dividends … in reduced weight, size and power consumption."

 Just read what the experts had to say about the Hitachi SR-903.

"What really makes you sit up and take notice of this receiver is its fantastic power reserve."

StereoMagazine

"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."

High Fidelity Magazine

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)