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, 4700
Ω
High
Gain: 56 dB
Signal-to-Noise
Ratio: 73 dB
Separation: 60 dB
Low
Gain: 46 dB
Signal-to-Noise
Ratio: 82 dB
Separation: 70 dB