Augustica
®
T e c h n o l o g i e s
Page 4 of 7
forms the load resistance, while the voltage division provided by the resistor pair allows
the grid bias to be set to the proper level. The bias voltage is decoupled from the load and
stabilized by resistor R9 and capacitor C3 before being applied to the grid of the second
section of 6922. The anode current flowing through resistor R6 to the triode, which
depends on the grid voltage and corresponding characteristic curve, generates a voltage
across the combination of R7 and R8 that is exactly proportional to the current. This
voltage is in turn fed to the headphone via coupling capacitor C5. Resistor R12 holds the
output at ground potential for DC signals in order to avoid crackling noises when the
headphone is plugged into stereo jack.
P
OWER
S
UPPLY
-T
HEORY OF
O
PERATION
The power supply for the headphone amplifier Corvette
®
is shown in
Figure 1
. The
power supply uses two transformers (not shown on the schematic). The first transformer
is employed to provide high B-plus voltage applied to anodes of both sections of 6922
tubes and is connected to the terminal block K2. The second transformer is employed to
provide low voltage applied to filaments of 6922 and is connected to the terminal block
K3.
The high AC voltage produced by the first transformer is rectified by the rectifying
bridge D1-D4 and then smoothened by capacitors C15, C16, C17, and C18. The
capacitors connected in parallel with the diodes of the rectifying bridge D1-D4 suppress
high-frequency noise generated by the diodes of the rectifying bridge. The high DC
voltage then is applied to a MOSFET transistor that serves as a voltage regulator and AC
filter. Resistors R24 and R25 are responsible for a 15 second delay during which the high
B-plus DC voltage reaches its maximum level of 310 Volt. This delay is significantly
increases longevity of the 6922 lifespan. Finally, additional smoothening of the high B-
plus DC voltage is provided by capacitors C19 and C20. Red LED D7 serves not only as
high B-plus DC voltage pilot light, but also, together with resistors R26 and R27,
provides a minimum load and ensures that the high capacitance capacitors C16, C17,
C18, and C20 are discharged once the power supply is switched off, even if no load is
connected to the power supply.
The low AC voltage produced by the second (filament) transformer is rectified by the
rectifying bridge D8–D11 and then smoothed by capacitors C25, C26, C27, and C28. The
capacitors connected in parallel with the diodes of the rectifying bridge suppress high-
frequency noise generated by the diodes of the rectifying bridge. High stability filament
voltage of 6.3 Volt is produced in a simple manner using a low drop voltage regulator
IC2 LD1084V. Green LED D10 serves not only as a pilot light, but also, together with
resistor R30, provides a minimum load and ensures that the high capacitance capacitors
C26, C27, C28, and C30 are discharged once the power supply is switched off, even if no
load is connected to the power supply.
