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GainStation 1
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An output stage, which also operates in class A mode with over
6 mA of closed-circuit current, functions as a current amplifier.
The transistors and resistors utilized also had an enormous
effect on the audio quality. To facilitate selection, we assem-
bled several models and subjected them to extensive listening
tests. All this trouble more than paid off: the final GainStation 1
op-amp has a slew rate of over 100V/us—several times faster
than industrial op-amps. This is an absolute prerequisite for
clean, transparent and dynamic audio. Transients are depicted
with unparalleled accuracy, resulting in an open, airy and reali-
stic sound.
The clean stage is based on a fully discrete, balanced instru-
ment amplifier and also operates in class A mode. The special
circuit configuration ensures consistent frequency response at
virtually every gain setting. With its slew rate of over 200 V/us, it
is able to amplify fast transients and extremely high frequencies
with almost no distortion. An op-amp subsequently converts
the instrument amplifier‘s output signal into an unbalanced
signal, which is fed to the tube.
The tube type—a Sovtek® 12 AX7 LPS—was also selected after
extensive measurements and listening tests. This tube type
delivers an open, transparent sound, excellent noise values
and is especially reliable. A generously proportioned 2.2 µF
WIMA-MKP decoupling capacitor is utilized to ensure clean,
punchy low frequency response. An impedance converter adapts
the tube‘s high-impedance signal to the output stage, which
also utilizes fully discrete op-amps and can easily drive extreme
cable lengths. Coupling condensers were used as sparingly as
possible to avoid their inherent disadvantages such as diffuse
sound, slurring and loss of dynamics. Instead, servo circuits
were utilized to eliminate DC artifacts.
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