Introduction
Congratulations on your purchase of this API 500 format compatible
SSL VHD
TM
Pre Module.
This module has been specically designed to operate in a 500 format
rack such as the API lunchbox® or equivalent. In common with many
such modules, the nominal input/output level is +4dBu.
The VHD Pre is an immensely versatile recording and processing
device. It can deliver ultra clean SSL SuperAnalogue
TM
grade
recordings but also features a switchable VHD mode. SSL’s patented
Variable Harmonic Drive (VHD) system uses a 100% analogue signal
path to generate rich harmonic distortion. As you increase VHD input
gain, the Variable Harmonic Drive process introduces either 2nd or 3rd
harmonic distortion or a blend of the two to your source material. At
lower gain settings it adds gentle valve-style warmth or a touch of
transistor edge. As the gain is increased the more extreme the
distortion becomes until at high gain settings it delivers erce trashy
transistoresque grunge.
Operation
Please refer to the illustration opposite.
Signal LED
➊
The signal LED is a tri-colour LED that indicates level according to the
following table.
* The LED scale is selected from a jumper on the module PCB.
Gain Controls
➋
The red pot provides up to +75 dBs of gain, whilst the black pot
provides a variable mix of 2nd to 3rd harmonics (once the VHD-IN
switch
➌
is engaged).
The grey pot provides +/- 20dB of trim. Use this to control the output
when driving the VHD preamplier circuit.
High Pass Filter
➍
The High Pass Filter section is a switchable 18dB/Octave variable
lter. See the block diagram for the position in the circuit.
Switch Functions
➎
HI-Z Switches the preamplier impedance from 1.2KΩ to
10KΩ
+48v Applies phantom power, a tell tale red LED indicates
phantom power is active.
PAD Applies 20 dBs attenuation before the signal enters the
preamplier.
Ø Polarity switch inverts the polarity of the signal by 180°.
Using the preamplier
When the VHD button is not engaged, the preamplier has been
designed to give a transparent sound, great for sources such as
acoustic guitars, vocals and strings.
When the VHD button is pressed, the preamplier can be driven to
give a wide-range of overdriven sounds, ranging from subtle to... well,
not so subtle! Drums and electronic instruments can oen benet
from VHD colouration.
The best way to drive the VHD preamplier is to increase the input
gain (red pot) whilst using the Line Trim pot to reduce the overall level
and not clip the channel output. Remember, it’s the input to the
preamplier that likes being driven. From this point, adjust the
harmonics to ne-tune the desired sound.
Block Diagram
Signal LED
VHD In
Switch
High Pass
Filter
Gain Controls
➌
➊
➍
➋
Switch
Functions
➎
LED colour +24dB Scale* +18dB Scale*
Green -24dBu -24dBu
Yellow +4dBu 0dBu
Red +21 dBu +16dBu
