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)
I have this one - the lights are long gone but the sound is very powerful and balanced. Amazing for an amplifier over 40 years old! I read that all the components were made in-house by Hitachi. They are not hard to find secondhand if you are patient, highly recommended.
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