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

Harman/Kardon HK 725 pre-amplifier

Harman Kardon introduces low negatiwe feedback design for inaudible TIM distortion
For the last few years,, audio manufacturers have been rushing to bring you newer,lower T.H.D. levels in their amplifier sections. And every year, they've accomplished this the simplest way they could. By adding negative feedback, a form of electronic compensation. Unfortunately, this "cure" for T.H.D. - typically 60 - 80 dB of negative feedback - creates another form of distortion. Transient Intermodulation Distortion, or TIM, which does far more to degrade the music than T.H.D. at Harman Kardon, we lowered T.H.D. the right way. With unique circuit design (US Patent #4.176.323) that lets us use just a fracrtion of the negative feedback typically used. The result is our new HK 700 series High Technology Separates. Built around our low negative feedback amp/preamp combination that delivers a crystal clear, totally transparent 65 watts per channel. You can also choose from a full-featured digital tuner, a phase locked analog tuner, and the most advanced cassette deck on the market.

The HK 725 High Technology pre-amplifier
Many of the critics from the most widely recognized audiophile publications consider the HK 725 one of the best preamplifiers on the market
As with all our components, the KH 725 was designed with careful attention to even the finest details. Instead of the typical 4-stage phono section, we used 8 stages. And we used FET front ends on both our low and high level stages. These provide higher Signal-to-Noise ratio than other designs. Instead of conventional rotary tone controls, we used fixed resistor push-buttons because they provide lower distortion. The HK 725 also allows you to defeat the tone controls altogether, giving you the clearest, cleanest sound possible.
Even our volume controls is unique. With twelve wipers instead of the usual four. This extra bit of engineering not only provides a smoother acting, longer lasting control, but also helps lower distortion as well. And we didn't forget convenience. You get facilities for two tape decks, with 2 way tape copy that allows you to monitor any source you like while copying from one deck to another. Plus loudness, subsonic and high cut filters to help you contour your system to your listening environment.
The Harman kardon HK 725 stereo preamplifier is housed in a relatively small metal cabinet that matches its associated model HK 770 power amplifier. Individually, or in conjunction with the power amplifier, the sound quality is best described as "exceptionally clean" particularly with respect to the deep bass. An unusual feature is switch-selected bass and treble equalization, rather than rotary controls. The bass and treble have eight switches each, four providing boost in steps of 2 dB at 50 Hz and 10 kHz; four providing attenuation in 2 dB steps at the same frequencies. An illuminated switch in the center of each row of buttons provides a tone control defeat. Subsonic and high cut filters round out the equalization. Switching is provided for automatic tape duplication from, or to, either of two recorders. A panel-mounted headphone jack allows the signal to be monitored without going through the associated power amplifier. One unswitched and two switched AC convenience outlets are provided.
Frequency Response : less than 1 Hz to beyond 150 kHz   +0 -1 dB
Total Harmonic Distortion: 
Phono :  0,009%
High Level :  0,005%
Intermodulation Distortion:  0,009% at 2 volts output
RIAA Equalization:  ±2 dB (20 -20,000 Hz)
Signal-to-Noise Ratio:
Phono :  90 dB IHF-A
High Level :  106 dB IHF-A
Phono Overload:  250 mV at 1 kHz
Input Sensitivity/Impedance:
Phono :  2,3 mV/47 k Ω
High Level :  145 mV/23 k Ω
Slew Rate:  Greater than 200 volts/µsec to output with IHF standard
Tone Control Range
Low :  ±8 dB at 50 Hz
High :  ±8 dB at 10 kHz
Dimensions (W x H x D):  385 x 72 x 320 mm (15,2 x 2,9 x 12,6 inches)
Weight:  4,2 kg (9,25 pounds)

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