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

Denon PMA-770 amplifier

Zero Dynamic Distortion

A Non-negative feedback amplifier design is ideal for driving speakers properly. Since audio signals are amplified in one direction only, the primary causes of dynamic distortion, such as time delay, are eliminated. Static distortion, which is caused by the non-linear amplification characteristics of amplifying components such as transistors, is reduced to almost theoretical limits by Denon's Distortion Servo Circuit.

Because of Denon's Non-Negative feedback technology and Distortion Servo-Circuit, the dynamic or pulsive music signals (those that change every moment in level and frequency) can be driven at high power through the widest variety of loudspeakers with surprising clarity and resolution.

The circuit is made up of 3 stages of low noise FET differential amplifiers. In the first stage current mirrors operate as the voltage amplification stage. The complementary emitter follower permits low impedance to be obtained; and is separated completely from the current amplification stage. The current amplification stage, a push-pull output configuration uses high quality, high speed power transistors, providing the speed and accuracy required for accurate reproduction of the original signal.


High Efficiency "Direct-A"  Power Amplifier

At the output stage, the Denon developed "Zero-Cross Linear Bias Circuit" eliminates switching distortion caused by the turning On and Off of the power transistors. This circuit enables the PMA-770 to combine both the sound quality of Class A with the high efficiency associated with Class B amplification.


Clean Layout and Simple Circuit Construction

The basic construction of the PMA-770 circuit has purposely been kept clean and simple as possible. The entire signal route is totally capacitorless. Even when using MC cartridges, the PMA-770 does not place a single capacitor in the main signal route, all the way from the input to the speaker output. This design speeds up while maintaining the purity of the signal and is what Denon describes as totally "DC construction"

The amplification circuit is of the dual FET differential type, resulting in greatly improved Signal-to-Noise Ratio and reduced distortion. Additionally, the employment of Denon's Direct DC Servo Circuit shut out DC drifts and stabilizes the ultra-low frequencies.



Power Amplifier Section

Circuit Type:  All stage direct DC servo circuit

Rated Output Power (Both Channel Drive)

100 W + 100 W at 20 Hz to 20 kHz 8 0hm load (DIN, U.K. Europe, USA)

150 W + 150 W at 1 kHz , 4  load (DIN, U.K. USA)

50 W + 50 W at 1 kHz, 4   Load (IEC)

Total Harmonic Distortion :

0,008% (20 Hz - 20 kHz at -3 dB rated output 8   Load)

0,02% (20 Hz - 20 kHz at rated output 8   Load )

Intermodulation DIstortion :  0,002% below 7 kHz/ 60 Hz : 1/4 (at amplitude output equivalent to rated output)

Output Bandwidth:  5 Hz - 100 kHz (IHF T.H.D. 0,035%)

Transmission Characteristics:  1 Hz - 250 kHz +0 dB -3 dB (at 1 W output)

Input Sensitivity:  150 mV

Input Impedance:  47 k

Output Impedance:  0,08   (1 kHz)

Output Terminals: 

Speaker A and B Load 4 - 16 or A + B Load 8 - 16

Headphone/Stereo headphone

Equalizer Amplifier Section

Max. Output:  10 V (at 47 k   load)

Rated Output :  150 mV

Total Harmonic Wave Distortion :  below 0,002% (at 1 kHz, 8 V output)

Input Sensitivity/Impedance

Phono MM :   2,5 mV/47 k

Phono MC :  125 µV/100

Tuner :  150 mV/47 k

Aux, Tape :  150 mV/47 k

RIAA Deviation:

Phono MM :  within ±0,2 dB (20 Hz - 100 kHz)

Phono MC :  within ±0,2 dB (20 Hz - 100 kHz)

Overall Characteristics

Signal-to-Noise Ratio (IHF A network)

Phono MM 1, 2 :  90 dB (input terminals short-circuited for 2,5 mV input)

Phono MC :  73 dB (input terminals short-circuited for 250 mV input)

Tuner, Tape, Aux :  110 dB (input terminals short-circuited)

Tone Control Adjustable Range

Bass :  ±8 dB at 100 Hz

Treble :  ±8 dB at 10 kHz

Subsonics:  18 Hz at 6 dB/oct


Low Frequency :  +7 dB at 100 Hz

High Frequency :  +6 dB at 10 kHz

AC Outlet:  switched x 2 100W Total, unswitched x 1 250 W

Power Requirements:  AC 120 V, 200 V, 220 V, 240 V 50/60 Hz

Power Consumption:270 W (USA); 400 W (IEC); 290 W (Hong Kong); 800 W Maximum Output

Dimensions (W x H x D):  434 x 132 x 407 mm

Weight:  12 kg


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