Solid State Logic Alpha VHD Pre Manuel D'installation page 9

Using VHD
VHD – Variable Harmonic Drive™ – allows a signal (microphone or line) to be over driven from subtle harmonic
colouration through to full on distortion. The level of the incoming signal will have an affect on the VHD circuit, as will
the PAD button which offers 20db of gain reduction for loud signals, allowing the Alpha VHD Pre to work with line as
well as microphone level signals.
Each Alpha VHD Pre input features a control labelled 'VHD' with a range of adjustment indicated as '2
Adjusting the VHD control changes the character of the added distortion from predominately 2
entirely 3 harmonic when fully clockwise; interesting blends between the two can be achieved at intermediate settings.
rd
The character of 2 harmonic distortion is akin to the warmer sound produced by overdriven valves whilst 3
nd
harmonic distortion is associated with the harder, brighter sound achieved from solid state devices.
The VHD control will have a far more noticeable effect at higher gain settings so the input gain should be used in
combination with the VHD control to affect the amount of distortion being added to the input signal. The PAD button
will glow red when the input stage is starting to overload; the VHD circuit is designed such that this is part of the
normal operation, though this should be avoided for a cleaner signal.
An over driven pre-amp may obviously have an effect on the gain of all parts the signal chain which follow the unit
and the output gain may need to be taken down to interface correctly with other equipment. The output level control
makes this adjustment a simple process.
' to '3 '.
nd rd
harmonic to almost
nd
rd
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