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 M-50

 Introducing the Pure Zero Distortion Rule Sound
Her, at  last, ia a power amplifier output stage that actually adds no distortion to the music signal. Although the actual technology involved in the Zero Distortion Rule amplifier is quite sophisticated, the basic principle of this incredible high-accuracy amplifier is quite simple. Essentially the Zero Distortion Rule system consists of a distortion detector and a summer. The distortion detector derives a signal corresponding to any distortion products originating in the amplifier itself, and the summer adds this signal back into the original audio/distortion signal - out of phase with the original signal. This effectively  cancels the distortion signal, leaving the audio signal intact and virtually distortion-free. Of course, this system has no effect on distortion originating in the source signal, only on distortion generated within the power amplifier itself. From the above description we can see that if the derived out-of-phase distortion signal were somehoe made larger than the original distotion signal, summing these signals would actually result in a negative distortion product. With this ingenious system, it has become possible to produce a power output stage that actually exhibits no inherent distortion.
 The Yamaha Zero Distortion Rule Amplifier vs. Negative Feedback and Feed Forward Systems
Negative feedback is the most commonly used means for reducing distortion in audio amplifiers. The amount of distortion reduction, however , is directly controlled by the amount of feedback applied. This means that in order to reduce distortion to zero, infinite feedback must be appliedd. Obviously, it is physically impossible to create infinite negative feedback, and therefore also impossible to achieve zero distortion by this method,. Increasing application of negative feedback can only approach the zero distortion ideal, while ZDR actually permits crossing the zero distortion line and creating negative distortion, making it theoretically possible to completely eliminate distortion.
The feed forward system of distortion reduction attemps to cancel distortion by adding an inverted distortion signal to the audio signal to the audio signal at the amplifier's output where signal power levels are high.
This means that expensive, high-power feed forward circuitry is required, and overall power efficiency is extremely low.  Also, the high-power feed forward amplifier required can actually add unwanted distortion. Zero Distortion Rule performs its distortion cancellation ata the amplifier's inputs thereby eliminating the power problem. And since the ZDR circuit is essentially concerned only with low-level signal, it cannot add any distortion of its own.

Linear Transfer Bias Circuit
Another feature of the M-50 power stage is its Linear Transfer Bias circuitry. This unique bias syatem minimizes crossover distortion due to non-uniform linearity between the power transistors in a push-pull power stage. By applying precisely calibrated bias to each transitor in the M-50's cascoded push-pull power circuit and thereby staggering the operating point of each, a perfectly linear composite transfer characteristic is achieved, ensuring negligible crossover distortion levels. The unbeatable combination of the Linear Transfer Bias circuit and Zero Distortion Rule amplifier design results in outstanding low-distortion power performance and incredibly natural source reproduction.
 "X" Power Purity
The concept of "pure power" is extremaly important in achieving the highest power amplifier performance. That is, the power source that supplies power to the actual power amplification circuitry must by capable  of providing extremely stable power, and at the same time supply as much power as the amplifier circuitry demands without "running out".
The Yamaha "X" power supply easily meets the above requirements, with greater efficiency and power capacity than aby other power system of its size or weight. In principle, the "X" power supply controls the amount of power fed from the AC line to the power  supply to precisely match the amount of power consumed by the amplifier at any given instant. Whether the amplifier requires only a small amount of power for average music levels, or a large amount for high-level music levels, or a large amount for high-level music peaks, the "X" power supply feeds precisely the required amount of power to the amplifier circuitry. Naturally, this means that all the supplied power is consumed achieving remarkable power efficiency.
In terms of stability, the "X" power supply affords exceptionally high regulation capabilities. Line supply voltage variations of as much as ±10% have no effect on the "X" power supply's output voltage, and resistance to influence by load variations is similarly high. The "X" power supply system permits the amplifier circuitry to operate at optimum efficiency under optimum conditions at all times, ensuring that the music source is reproduced with maximum accuracy.

Speaker Level Controls
In addition to a speaker A/B selector that permits one-touch selection of two sets of stereo speakers, the M-50 features speaker A and B level controls. These controls let you independently set the maximum power level that will be sent to the respective pair of speakers, protecting low-power-capacity speakers from excessive power levels, or matching the output level of two sets of speakers of different efficiency.

20-LED Peak Power Output Meters
These bright, attractive power meters let you see at a glance just how much power is actually being fed to ypur speakers. This makes it easier to determine the proper setting of the speaker level controls to prevent speaker breakup distortion or burnout due to power levels exceeding the speakers capacity.

Minimum RMS Output per Channel: 
120 Watts (8Ω, 20 to 20,000 Hz no more than 0,002% THD)
200 Watts (4Ω, at 1 kHz, clipping Power)
Power bandwidth (8Ω, Half rated power):  10 to 100,000 Hz (0,02% THD)
Input Sensitivity/Impedence (8Ω, rated power):  1,1 V/25 kΩ
Frequency Response (8Ω Half rated power, 100 kHz):  -0,5 dB
Signal-to-Noise Ratio (IHF A network):  122 dB
Total Harmonic Distortion (8Ω Half rated power):
20 Hz : 0,0005%
1 kHz : 0,0005%
20 kHz : 0,001%
50 kHz : 0,004%
100 kHz : 0,01%
Intermodulation Distortion (8Ω Half rated power 50 Hz : 7 kHz = 4;1): 0,002%
Channel Separation (8Ω Half rated power , Input Shorted):
20 Hz : 100 dB
1 kHz ; 95 dB
20 kHz : 70 dB
Damping Factor (8Ω 1 kHz):  Better than 200
Slew Rate (Sp Out):  200 V/µsec
Power Supply:  Matched to supply voltage and frequency of all area
Power Consumption:
USA and Canada : 350 W/1,200 VA
Europe and Australia : 550 W
Other Areas : 200 W
Dimensions (W x H x D):  435 x 133 x 380 mm (17-1/8" x 5-¼" x 15")

Weight:  11,8 kg (26 lbs)

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