Yamaha
M-70
The Pure
Zero Distortion Rule Sound
Here, at
last is a power amplifier output stage that actually adds no distortion to the
music signal. Although the actual techno;ogy involved in the ZDR (Zero
Distortion Rule) amplifier is quite sophisticated, the basic principle of this
incredibile high-accuracy amplifier is quite simple. Essentially the Zero
Distortion Rule system consists of a 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 somehow made larger than the original distortion 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.
Zero
Distortion Rule vs. Negative Feedback
Negative
feedback (NFB) 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 applied. 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.
Zero
Distortion Rule vs. Feed Forward
The feed
forward system of distortion reduction attemps to cancel distortion by adding
an inverted distortion signal to the audio signal at the amplifier's output
where signal power levels are high. This means that expensive, hig-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 at
the amplifier's inputs, thereby eliminating the power problem. And since the
ZDR circuit is essentially concerned only with low-lwvel signals, it cannot add
any distortion of its own.
Linear
Transfer Bias and the "X" Amplifer
In
addition to the ZDR system, the M-70 feature Linear Transfer Bias circuitry and
Yamaha's remarkable "X" Power Amplifier system. The Linear
Transfer Bias circuit minimizes the problem of crossover distortion due to
non-uniform linearity between the power transistors in a push-pull power stage.
By applying precisely calibrated bias to each transistor in the M-70'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
"X" Power Amplifier achieves extremely high amplification efficiency
by switching the power supply voltage between two voltage levels - low and high
- according to the size of the signal being processed. For average signal
levels, for example, the lower supply voltage is used, while the high supply
voltage is instantaneously switched in whenever a high-level music peak is
detected. This system eliminates the power wasted in the form of heat that
conventional systems must dissipate with large, finned "heat skins".
The fact that the "X" Power Amplifier permits true high-power music
amplification with maximum efficiency and minimum heat generation means that
the entire amplifier circuit operates under optimum conditions at all times,
ensuring the cleanest most accurate music reproduction. The unbeatable
combination of the Linear Transfer Bias circuit, "X" Power
Amplification, and Zero Distortion Rule amplifier design results in outstanding
low-distortion power performance and incredible power efficiency for unmatched
reproduction precision and exceptionally natural sound quality.
"X"
Power Purity
The concept of "pure power" is extremely important in
achieving the highhest power amplifier performance. That is, the power source
that supplies power to the actual power amplification circuitry must be capable
of providing extremely stable power and at the same time supply as much power
as the amplifier circuitry demends without "running out".
The Yamaha "X" power supply easily meets the above
requirements, with greater efficiency and power capacity than any 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 supply to precisely match the amount of
power consumed by the amplifier requires only a small amount of power for
average 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 speaker A/B selectors that permit one-touch selection of two sets
of stereo speakers, the M-70 features independent level controls for the left
and right speakers in two stereo pairs. That is, you have independent left and
right speaker level controls for speaker pair "A", and left and right
level controls for speaker pair "B". 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. Independent control over left and right speaker level lets you
preset the balance of your system for optimum stereo imaging depending on the
positioning of your speakers and the acoustics of your listening room.
20-LED
Peak Power Output Meters
These
bright, attractive power meters let you see at a glance just how much power is
acctually being fed to your 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 speaker's capacity.
zFor easier reading, these advanced meters feature dual switchable ranges and s
peak hold function that displays the highset encountered power levels for
considerably longer than the overall meter fall time.
Specifications
Minimum RMS
Output per Channel:
200
Watts (8 Ω, 20 to 20,000 Hz no more
than 0,002% THD)
250
Watts (4 Ω, at 1 kHz, clipping Power)
Power
bandwidth (8 Ω, Half rated
power): 10 to 100,000 Hz (0,025 THD)
Input
Sensitivity/Impedence (8 Ω, rated
power): 1,41 V/25 k Ω
Frequency
Response (8 Ω Half rated power, 100
kHz): -0,5 dB
Signal-to-Noise
Ratio (IHF A network): 124 dB
Total
Harmonic Distortion (8 Ω Half rated
power):
20 Hz :
0,0005%
1 kHz :
0,0005%
20 kHz :
0,001%
50 kHz :
0,003%
100 kHz :
0,006%
Intermodulation
Distortion (8 Ω Half rated power 50
Hz : 7 kHz = 4;1): 0,002%
Channel
Separation (8 Ω Half rated power ,
Input Shorted):
20 Hz : 100
dB
1 kHz ; 95
dB
20 kHz : 70
dB
Damping
Factor (8 Ω 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 : 600 W/1,200 VA
Europe and
Australia : 900 W
Other Areas
: 550 W
Dimensions
(W x H x D): 435 x 133 x 380 mm
(17-1/8" x 5-¼" x
15")
Weight: 13,7 kg (30 lbs 3 oz)
