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 C-70

 The Ultimate in Control and Performance
The Yamaha C-70 Stereo Control Amplifier reflects an immense amount of research and development, vast technological resources and years of accumulated experience in Natural Sound amplifier design. The remarkable C-70 features a new Extended Rolloff Equalizer that eliminates much of the high-frequency phase deviation of conventional phono equalizer designs, a New Linear Transfer circuit that minimizes current distortion caused by semiconductor non-linearity in class-A amplification stages, completely independent preamplifier stages for moving magnet and moving coil cartridges ensuring the best possible performance with each type, a unique Varigain volume control system that completely obviates the problems associated with conventional attenuator-type volume controls, a full two-band parametric equalizer for precise response tailoring, and a unoque inverted output feature that makes it easy to set up a number of top-performance reproduction systems. In addition to all these advanced performance and versatility oriented features, the C-70 features the most exacting, highest-quality design and construction throughout. Careful attention has been paid to the smallest details, like making sure that the connector terminals are non-magnetic, in addition to being gold-plated, so magnetic fields generated by the audio signal in the connector terminals cannot affect sound quality.  In the Yamaha C-70 you get a sophisticated stereo control amplifier capable of providing the finest reproduction performance in any sound system - even fully professional setups.
 2-Band Parametric Equalizer
The parametric equalizer format is undoubtedly the most comprehensive, precise means of tonal response tailoring available today.  Although it is a fairly recent development in the sound reproduction field, the parametric equalizer is preferred for response control in the world's most sophisticated professional recording studios. The reason for the parametric equalizer's popularity in professional circles is that, unlike previous equalizer systems, it provides independent, continuously variable control over frequency, bandwidth and level. That is, you can set any center frequency for a range of frequencies you need to equalize, you can set the bandwidth to precisely cover the frequency range to be equalized, and like conventional equalizer systems, you can precisely set the desired amount of boost or cut in the frequency range determined by the frequency and bandwidth controls (Bandwidth is called "Q" in some professional parametric equalizer systems). The parametric equalizer system provided in the C-70 gives you the same type of response tailoring flexibility offered by professional systems. Two bands of equalization are provided: one which covers a frequency range of fron 31,5 Hz to 800 Hz, and the other with a frequency range of 800 Hz to 20 kHz. You have continuously variable control over the bandwidth of each frequancy band (Q = 0,3 - 3), and +/_12 dB boost/cut control in each band.  This equalizer system gives you incredibily broad control over reproduction response, letting you create precisely the response you need for the most accurate music reproduction in any listening environment.
 Varigain Volume Control
The volume controls used in conventional amplifiers are "attenuators". This means that they perform their volume reduction function by shunting an appropriate amount of the audio signal to ground. Unfortunately, this type of volume control has a number of limitations in terms of achieving optimum sound reproduction quality: 1.Volume reduction generally reduces only the level of the audio signal, leaving the amplifier's residual noise to obliterate musical detail when listening at low volume (the Yamaha four-gang volume control used in the C-50 eliminates this problem). 2.Using a potentiometer to shunt portions of the audio signal to ground results in mid-circuit impedance variations that can affect response and distortion characteristics.  The Yamaha Varigain volume control system overcomes the above problems by actually varying the gain of the amplifier to control volume instead of bleeding off a portion of the music signal. Since the gain of the amplifier is reduced to lower volume, the amplifier's residual noise is naturally reduced, while at the same time maintaining the highest possible signal-to-noise ratio at all volume levels. Further, the Verigain system produces no impedance variations so distortion and response characteristics are optimum at aall volume settings. Although this seems to be a relatively obvious improvement in amplifier design, it took Yamaha ingenuity and attention to detail to implement the Varigain volume control for your listening pleasure.
 New Linera Transfer Circuit
Although push-pull class-A-bias amplification stages offer overall reproduction accuracy greater than classB configurations, conventional versions of this circuit suffer from current distortion due to the fact that the "gm" (mutual transconductance) curve of any semiconductor is distinctively non-linear outside its ideal flattest portion.  Signals falling outside the transistors flattest gm range become distorted.  Yamaha engineers found a way to minimize this type of distortion in the New Linear Transfer circuit. This advanced circuit adjusts the bias to the size of the input audio signal, thereby ensuring that the semiconductors linear gm range always corresponds to the audio signal being processed. This means that an absolute minimum of current distortion is assured with any input signal. In the C-70, all amplification stages from the phono equalizer to the output stage feature the Yamaha New Linear Transfer system.
ERE (Extended Rolloff Equalizer)

With the vast improvements in overall amplifier performance, the time has come to provide an RIAA equalizer capable of equally fine performance. Today's low-level flat-response amplifiers easily achieve virtually distortion-free response up to 100 kHz or more. Conventional RIAA equalizer amplifiers, however, come nowhere near this outstanding performance. The Yamaha Extended Rolloff Equalizer meets the modern performance standards by eliminating phase variation beyond the range where conventional equalizers begin to deviate from the RIAA curve. This type of extended equalizer accuracy was previously impossible to achieve because of high-frequency instability limitations. The Yamaha ERE completely eliminates this instability while providing an accurately extended high-frequency curve, permitting greater reproduction precision than has ever been possible. The ERE circuit further incorporates a built-in 12 dB/oct subsonic filter that makes clean, unmuddied reproduction possible down to a low 10 Hz. The Yamaha ERE circuit makes a difference in phono reproduction that you can hear. And it's a difference you'll really appreciate because you'll discover nuances and subtleties in the music on your favorite records that you may never have heard before.

Inverting Preamplifier Outputs

This highly original Yamaha feature gives you incredible flexibility in planning and setting up a true "audiophile class" sound reproduction system. Used in conjunction with the C-70's standard non-inverting outputs, the inverting preamplifier outputs let you use two stereo power amplifiers - one for each channel - to achieve pro-class power output and aound quality; you can couple the left and right channels to your power amp in invers phase, and reverse the phasing of your speakers to increase power efficiency and achieve incredibly natural bass reproduction. You can experiment to find the system that is just right for ypur listening needs. Whether you end up with one of the advanced systems described here, or a standard component setup, the C-70 guarantees you the finest, most "live" music reproduction performance available.
Direct Phono Inputs
For the purest, most natural disc reproduction performance, the C-70 provides input terminals for moving magnet and moving coil cartridges that feed directly to their respective head/EQ amplifiers without being routed through the phono 1 / 2 switch as are the Phono 1 and 2 inputs. This means that switch contact resistance in this critical low-level high-gain stage cannot affect disc reproduction quality.

Other Features:  
Selectable MM cartridge load capacitance.  Rec Out selector.  Disc Direct function.  Solenoid/relay function switching.  Dual AUX terminals.  Flip-down control cover.  Switchable 10 kHz high filter.  Switchable 15 Hz subsonic filter.  Phono 1/2 selector.  Stereo/Mono mode selector.  Optional EIA rack mount adaptors.

Input Sensitivity/Impedance: 
Phono MC : 100µV/100 Ω
Phono MM : 2,5 mV/100 Ω
100 / 220 / 330 pF : 2,5 mV/47 k Ω
Aux, Tape, Tuner : 150 mV/47 k Ω
Input Sensitivity (New IHF):
Phono MC : 33µV
Phono MM : 0,83 mV
Aux, Tape, Tuner : 50 mV
Maximum Input level (1kHz, 0,01% THD/New IHF)
Phono MC : 13 mV/11 mV
Phono MM : 300 mV/260 mV
Output Level/Impedance:
Rec Out : 150 mV/470 Ω
Pre Out : 1,5 V/47 Ω
Maximum Output level (20 -20,000 Hz, 0,1% THD)
Pre Out : 10 V
Headphone Maximum Output level/Impedance (1 kHz,0,01% THD, Output Impedance 68 Ω):
0,48 V /8 Ω
4,5 V /100 Ω
Frequency Response  (Aux, Tape, Tuner to Sp Out):  5 to 100,000 Hz +0 -0,5 dB
RIAA Deviation:
Phono Mc : 20 to 20,000 Hz ±0,2 dB
Phono MM : 10 to 100,000 Hz ±0,3 dB
Total Harmonic Distortion:
Phono MC to Rec Out 3 V output : 0,001%
Phono MM to Rec Out 3V output : 0,001%
Aux, Tape, Tuner to pre Out 5V output (Tone switch Off) : 0,001%
Intermodulation Distortion (Aux, Tape, Tuner 5V output. Tone Switch Off):  0,002%
Signal-to-Noise ratio (IHF-A Network/New IHF)
Phono MC (500 V, Input Shorted) : 90 dB / 80 dB
Phono MM (500 V, Input Shorted) : 94 dB / 82 dB
Aux, Tape, Tuner (Tone switch Off) : 105 dB / 104 dB
Residual Noise (IHF-A Network):  1,8µV
Channel Separation
Phono MM/Aux, Tape (5,1 k Ω, Input Shorted)
40 Hz, 1 kHz, 10 kHz : 85 dB/100 dB;  80 dB/70 dB;  70 dB/60 dB
Parametric Equalizer Characteristics
Frequency Control  (Low / High) :  31,5 -800 Hz / 800 Hz - 20 kHz
Level Control (Low / High):  ±12 dB
Bandwidth Control (Low / High):  Q: 0,3 to 3,0
Subsonic Filter Characteristics:  15 Hz , -12 dB/oct
High Filter Characteristics:  10 kHz, -12 dB/oct
Audio Muting:  -20 dB
Tone Control:
Bass (boost/cut)
Treble (boost/cut)
Turnover Frequency:
Power Supply:  110 -120 V, 220 - 240 V AC 50/60 Hz
Power Consumption:  50 W
Dimensions (W x H x D):  435 x 96,5 x 369 mm (17-1/8" x 3.¾" x 14-½")
Weight:  7,2 kg (15 lbs 13 oz)

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