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what to listen for when you resume listening to your speakers. If you wish to mute your main speakers not to listen to Headphones but
while a second pair of speakers is active in a multi-room application via the Preamp Output, we recommend adjusting the multi-room
volume with the Level Set attenuator, leaving the Master Volume control at the lowest possible setting. This avoids running the load
resistor of the Headphone circuitry unnecessarily hot. Should
you own Headphones so efficient that the usable gain range is
restricted to just a few “clicks” on the Volume control, select
one of the higher stages of Feedback and/or more treble activ-
ity. This procedure decreases overall output and widens the
usable range of the Attenuator.
WARNING: Similar to the warning signs in your car’s review
mirror ( objects are closer than they appear ), volume levels
during headphone listening are often higher than they might
appear. This is especially true after prolonged listening sessions, when listener’s fatigue reduces
our sensitivity and we compensate by increasing the volume. Abnormally elevated playback levels during headphone listening can
permanently damage your hearing!
The TIGRIS uses cathode biasing for its power tubes and thus no adjustments are ever required. This is one of the invisible features
we mentioned in the Introduction and it is attractive because it removes the need to monitor and maintain the biasing of the power
tubes. Cathode biasing is so effective it is also known as self biasing or Auto Biasing. For the technically minded who want to know
more about Bias techniques, here is a brief explanation:
A tube’s operating conditions are established by striking a balance between attracting and repelling forces. Remember, unlike charges
attract, like charges repel. At the center of the tube is the cathode which, when heated, emits a cloud of electrons. Possessing an
inherently negative charge, these electrons are strongly attracted to the plate (or anode) which is charged to a high positive voltage
from the main power supply. Located in between the cathode and the plate is a spiral of thin wire called the control grid. In order to
restrict the flow of electrons from the cathode to the plate, the plate is made to be more negative than the cathode. Because like
charges repel, negative electrons from the cathode are both repelled by the more negative grid and attracted by the highly positive
plate. A small change in the negativity of the grid can cause a large change in the amount of electrons flowing to the plate. And that’s
the essence of amplification: a small change in the grid voltage causing a large change in the plate current.
But first, a proper zero-signal, static state current flow must be established and that is accomplished by achieving the proper relation-
ship of voltages between the cathode, plate and grid.
In a fixed bias system, such as the BARON, the power tube cathodes are tied directly to ground at zero Volts. A negative voltage from
a separate small power supply is then applied to the control grids and that voltage ( called the Bias voltage ) is set such that a
predetermined idle current flows through the power tubes under zero-signal conditions. The more negative the grid is with respect to
the cathode, the less idle current will flow through the tube to its plate.
In a self-bias system, such as the TIGRIS, the power tube cathodes are tied to ground - not directly - but through resistors. When
current flows through the tubes, a voltage drop occurs across these cathode resistors and this provides a positive voltage on the
cathodes. The control grids may then be operated at a zero D.C. voltage - but they will still be negative with respect to the cathodes
because the cathodes are now slightly positive.
5 - 3 HEADPHONE OUTPUT: (Continued)
HEADPHONE
V
ACUUM
T
UBE
A
UDIO
HEADPHONES
SPEAKERS
5 - 4 AUTO BIAS:
Cathode...........................................0
Plate................................................+ 450
Grid..................................................- 50 (voltage generated by
separate power supply)
FRONT PANEL: TIGRIS
REAR BAY: TIGRIS