What is stereo?

There are now two system of high fidelity, monophonic (monaural) and stereophonic. Monophonic is a system that starts from one microphone and is fed through a single high fidelity set. Stereophonic is a double system. Two separate microphones are placed at different sides of the orchestra and two different systems are used to keep the two signals or channels separated. Two separate speakers are used, placed on different sides of you room. Stereo is much like 3-D photography, two slightly different sound reach your ears giving you a new dimension in sound.

H.H. Scott '59

Yamaha A-550

 The Latest Technology for the Best In Sound and Convenience
The Yamaha A-550 is a top-performance integrated amplifier offering the very latest in sound reproduction technology. The preamp section is constructrd with the lowest noise components and design for the cleanest possible reproduction with an absolute minimum of distortion. Whether your input is phono, tuner or tape, every delicate musical detail is brought to you with stunning accuracy.
The power amplifier is a pure complementary SEPP (Single Ended Push-Pull) design with current mirror circuitry and a bipolar power supply for exceptionally stable, accurate reproduction under even the most demanding conditions.
Direct coupled circuitry and an OCL (Output Capacitor Less) output stage assure that the signal sent to your speakers is as close as possible to a perfect image of the original input signal.
The A-550 specifications alone cannot give you an accurate idea of its superb sound quality, but your ears will certainly hear the difference. For convenience, the A-550 front panel is arranged so you can start up your system to monitor any input source by pressing just two buttons: power and the Input Select button of your choice. The Power and Input Select buttons are easy-handling illuminated types that show you the amp's operating mode at a glance.
The A-550 also offers fully independent recording and listening: a feature that lets you listen to any input source while recording from any other. There's even a convenient tape monitor/copy function that makes recording and dubbing continuously variable loudness control ensures that you get proper perspective tonal balance at any listening level.

For top-quality sound and convenience the A-550 is hard to beat. And its surprising affordability makes it a best buy.
 Ultra-Low-Distortion Design
In any sound system, distortion is the most detrimental element to accurate reproduction. The more distortion is present, the more the shape of the original music waveform will be altered, resulting in only a vague representation of the actual sound. And, of course, any distortion that appears at your speakers is the sum of all the distortion levels throughout your system. One weak link in the chain can make your expensive system sound like a bargain basement special.

The A-550, however, offers exceptionally low distortion throughout every stage - phono equalizer, preamp, tone control, and power amp - from input to output. Total harmonic distortion is no more than 0,02% at full power, from 20 Hz to 20 kHz. So no matter how hard you drive it, the A-550 delivers super clean, accurate sound.
 To maintain the A-550's superb 0,02% distortion figure even at full 40 watts per channel output, the power amp section is an advanced direct coupled OCL design with pure complementary SEPP, current mirror and bipolar power supply circuitry. There are no capacitors in the signal path to cause phase shift and distortion of the music waveform. And transient response is exceptionally fast so the sound is always crisp.

Since the cartridge output signal is so small, any noise present in this critical stage will be amplified many times before reaching your speakers. The A-500 phono equalizer provides the outstanding signal-to-noise ratio of 98 dB (IHF A Network). And since only the highest quality components are used in the RIAA equalization network, frequency response is ruler flat. This kind of superior equalizer performance lets you take full advantage of the high signal-to-noise ratio and extended frequency response of the latest direct-cut and PCM recorded discs.

Independent Recording and Listening
With most preamps and integrated amplifiers, when you record a source, or dub from deck to deck, you're stuck with the source you're recording or dubbing, i.e. you can't listen to anything else. Not so with the A-550. yamaha's original Rec Out selector lets you send any source to your tape deck while you listen to any other selected by the Input Select buttons. You can tape a friend's record while listening to your favorite FM program, dub tapes from deck to deck while listening to a record, or any other convenient combination.
 Built-in Subsonic Filter
High-level low frequencies generated by warped records or other sources can cause damge to your speaker system and sap vital power from the power amplifier. To eliminate this potential proble, the A-550 features a built-in subsonic filter that sharply cuts out these damaging frequencies without affecting overall sound quality.

Power Protection / Muting Circuitry
Since the A-550 power amplifier section can accurately handle signals virtually down to DC, a special power protection circuit has been incorporated which shuts down the output stage and speakers if any potentially damaging DC leakage is sensed at the output. This circuit also functions to prevent damage to speakers and the output stage due to the power shock surge that occurs when the unit is switched on.
Minimum Output Power (Continuous RMS Power per Channel):
40 W at 8 Ω, 20 - 20,000 Hz (IHF)
45 W at 4 Ω, 20 - 20,000 Hz (IHF)
53 W at 8 Ω, 1 kHz (DIN)
Total Harmonic Distortion:
Phono to Rec Out (3 V, 20 - 20,000 Hz) :  less than 0,005%
Tuner to Sp Out (20 W, 20 - 20,000 Hz) :  less than 0,01%
Intermodulation Distortion:
Tuner to Sp Out (8 Ω, 20 W, 60 Hz : 7 kHz = 4:1):  less than 0,005%
Power Bandwidth (8 Ω, 20 W, 0,05% THD):  10 Hz to 70 kHz
Damping Factor:  over 50 (8 Ω, 1 kHz)
Frequency Response:
Tuner, Aux, Tape 1 & 2 to Sp Out:  4 Hz to 70 kHz (+0 -2 dB)
RIAA Deviation:  40 Hz to 20 kHz (±0,2 dB)
Input Sensitivity/Impedance:
Phono :  2,5 mV/47 k Ω (220 pF)
Tuner, Aux, Tape 1 & 2 :  150 mV/47 k Ω
Maximum Input level:
Phono (1 kHz, 0,005% THD) :  over 200 mV
Tone Control Characteristics:
Bass (500 Hz) :  ±10 dB at 20 Hz
Treble (3 kHz) :  ±10 dB at 20 kHz
Output Sensitivity/Impedance:
Rec Out :  150 mV/600 Ω
Signal-to-Noise Ratio (IHF A network/New IHF):
Phono :  better than 98 dB (10 mV)/69 dB
Tuner, Aux, Tape 1 & 2 :  better than 104 dB / 83 dB
Residual Noise (volume minimum):  120 µV
Channel Separation (1 kHz):
Tuner to Sp Out (Input 5,1 k Ω) :  better than 65 dB
NDCR, phono to Sp Out:
IHF-A network, 0,1% distortion, vol at -20 dB:  12 mW to 40 W
Headphone Output:  50 mW (8 Ω, rated output)
Power Supplies:  models available for all supply voltages and frequencies
Power Consumption:
U.S.A. and Canada :  240 W, 310 VA
Australia and Britain :  290 W
Germany :  260 W
Other Areas :  240 W
Dimensions (W x H x D):  435 x 112 x 338 mm (17-1/8" x 4-1/2" x 13-1/4")

Weight:  7,8 kg (17 lb 2 oz)

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