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





Graaf GM 70 Phono Preamplifier

The philosophy of GM 7O phono stage design, is the most typical for GRAAF, followed for its whole production. It regards mainly the insertion of the active elements in an environment that is able to let them express their complete potential. The same importance is given to the full exploitation of each component own characteristics, so to avoid the use of additional circuits, which could interfere on the musicality of the performance. Therefore, RF filtering is obtained by the inner characteristics of active components used, and not with the recourse to a passive network. In the same way, in order to obtain the correct input sensitivity for MC cartridges, there is not any additional gain stage. Instead, a variable gain Implement has been chosen, because it has a simpler lay out and is more transparent to music.
RIAA eq is made by a completely passive network, placed after the gain stage. Its components have been calibrated with the greatest care to maximize the response precision and the purity of the musical signal, with the help of critical listening tests as well. Power supply implements the same transformers section of GM 13.5 B II, quite huge, followed by independent filtering for gain and RIAA stage, and for output stage.
The correct electric interface between cartridge and phono stage has been carefully regarded. The knob on the back side of the unit is for the selection of six different impedance loads. Wishing to have a custom load, it is possible to use the upper RCA plugs to connect a resistance of the proper value.
The input stage is based on two pairs of PC 9OO tubes. Gain stage and output buffer stage use a pair of 6922 tubes each, chosen for their linearity, low noise and musical characteristics. The active components used by GM 7O and the whole GRAAF production are subject to a very hard selection, that guarantee the full correspondence of each unit to the reference specifications.
Built manually one by one, with components selected with the greatest care, tested by a severe burn in procedure that go on no stop for several days, each one presented to the definitive approval of the designer in person, given only after a careful listening test, GRAAF electronics have all the qualities to fulfil the most discerning of the listeners, first of all for purity of sound and luminousness of timbre.

SPECIFICATIONS
Frequency response: 20 Hz - 20 kHz
50 KHz Attenuation: 28 dB.
100 khz Attenuation: 34,8 dB
Input Impedance: 38, 56, 100, 500, 1000, 47000. ohm
High Gain: 56 dB
Signal/Noise Ratio: 73 dB
Separation: 60 dB
Low Gain: 46 dB
Signal/Noise Ratio: 82 dB
Separation: 70 dB

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