Peavey Peavey ReValver MK III, Руководство пользователя

Страница: 41 / 45

The coupling capacitor removes the high voltage DC offset from the output signal of the tube
stage. This high-pass frequency is usually between 5-10 Hz, but if it is set higher then a user can
change the tonal and dynamic properties of the stage.
The grid resistor value is an all-in-one resistor used to calculate the effects of the stage’s band pass
limitation. Inside each tube there is an internal capacitance called “Miller capacitance.” The
greater the resistor, the lower the bandwidth. The bandwidth can be calculated at 1/(6.28*RC)
where R is the “grid resistor” and C is the Miller capacitance (usually around 150pF). In a normal
triode stage with a 12AX7 tube, the bandwidth is around 15 kHz if the grid resistor is 68 kOhm.
The slider for Class A/B is used for pentodes in push-pull configuration only. (The Bias voltage
slider can be used as an alternative.) This sets the bias of the tube stage such that it corresponds
more to a Class A or B stage.
Some of the non-physical tweaks:
Normally, a tube’s output swing is determined by the VPP, along with the various loads in the
cir cuit. Setting
Clip Limit to something higher than 1.0 gives the circuit a greater dynamic range.
The output gets higher and the distortion on one side decreases. Clip softness is used to smooth
out the sharp dynamic edge and gives the distortion a smooth sound.
The default value of the Dynamic Bias offset amount is 1.0, and scaling this value changes the
dynamics of the signal. The signal is usually not entirely free to move through the tube, and strong
transients and high volumes affect the bias of the tube, moving up and down, as a function of
volume.
Cathode biased treble boost (where applicable) changes the “filter effect” that the cathode
resistor & capacitor has on the frequency response.
The Bias adjust slider simply adds or subtracts a certain voltage to or from the tube’s bias. Other -
wise, this bias is defined by the tube and its surrounding components.
Extra input headroom gives the stage more dynamic headroom, making the tube distort later if
given a greater headroom. For a triode this means the signal is “attenuated” before the input and
“amplified” after the output, thus restoring the signal strength to the following tube.
The tube Tweak GUI features the following graphical displays: A “ bode plot” (frequency& phase
response) an oscilloscope (with input and output signal display overlaid) and “transfer function”
(a snapshot of the static input-to-output relationship).
The whole tube component can be disabled via the Disable circuit checkbox.
40