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Two band interactive Passive EQ
:
The two band passive EQ is intended as a final sweetener before the
signal is sent off to the output stage.As these hit the valve circuitry at different
points , enhancement takes place in the amount of harmonic content.The EQ
amounts intereact with the pad/gain control to provide an organic response
curve that includes both air and deep bands.By increasing the pad/gain control
the amount of air is decreased subtlely and the amount of deep is increased
proportionally.
*
Air Switch
.....Air is roughly situated over 10 khz , the amount of air interacts
slightly with the pad/gain control.As the pad/gain dial is turned up the amount
of Air is reduced approaching a more classic sound.
*
Deep Switch
....Deep is below 80 hz and increases as the pad/gain control is
increased (opposite of Air).
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Pad/Gain control
:
This function is based on negative feedback around the first stage of
the valve.With the pad/gain dial turned right down the Vamp four can handle
line signals of over +4dbm.By varying this parameter the amount of colour and
gain can be adjusted.With minimal gain the signal is clean and transparent
and is represented by the green LED.When the gain is turned up the signal
becomes increasingly coloured or distorted and this is evident when the yellow
LED begins to flicker or stay on.
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LED indicators
:
The LED indicators on the Vamp-Four are designed to give a visual
representation of the degree at which the valve is being driven.
Unlike Transistors and integrated circuits the nature of the valve is not to clip
immediately when driven past its linear region. Rather, valves tend to bend or
‘soft-clip’ any signals that push its input limits.This can have the effect of
slightly compressing the signal and generates warmth to the signal.
To indicate the degree at which the valve is being driven the two LEDs
are calibrated approximately 20db apart which is roughly the window of the
valves linear region.
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Output level
:
The output level controls the signal flow to the final output stage and is
used to properly set amount of signal sent to the next unit in the signal chain.
Additional gain is attained here so that the very front end can run transparently
without the loss of overall gain.
4/ Controls and indicators