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VHD+ Mic Preamplifier 500 Series Module

Variable Harmonic Drive (VHD) Mic Preamplifier for 500 Racks

SRP £429.00 + VAT

Delivery everything from ultra-clean to slightly warmed to heavily distorted recordings



The VHD+ Pre is an immensely versatile recording and processing device. It can deliver ultra clean SSL SuperAnalogue™ 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 fierce trashy bipolar transistor style grunge.


This new 500 series version features front and rear inputs with four different impedance selections making it an extremely versatile mic pre and DI box for a wide range of microphones and instruments.


The Mic Amp provides up to +75 dB of super clean gain. The VHD switch along with the Drive control provides a variable mix of 2nd to 3rd order harmonics to add warmth and colour to the signal.


A Trim control provides +/- 20dB of output trim, which allows the Mic Pre to be ‘driven’ and then the output dialled back to prevent overload of the next module in the chain.


An 18dB/Octave High Pass Filter provides a way to filter low frequencies such as floor rumble and is switched to bypass it from the signal path.


The front panel 1/4” Tip/Ring/Sleeve (TRS) Jack Socket provides a convenient way to connect instruments when the module is fitted in a rack. This balanced input overrides the rear XLR and has a 10KΩ input impedance and features an automatic -10dB level pad to allow for typically louder balanced line level signals. The Jack input can also be used with unbalanced (TS) cables such as those from synthesizers or guitars. The input level and impedance are switched to 0dB and 1MΩ respectively (for very high impedance sources such as guitar pick-ups) with selection of the HI-Z switch.


The rear XLR and front Jack inputs have different impedances available by using the Hi-Z switch and allow for a wide variety of sources. The rear XLR input impedance changes from 1.2 KΩ to 10KΩ for Hi and Lo Z Microphones. The front panel Hi Z switch changes the front Jack input impedance from 10KΩ for line sources such as keyboards to 1MΩ for sources such as electric guitars and basses.


Signal level is indicated with a tri-colour LED and the scale of the LED can be set between two -3dB overload points at +16 and +21dBu to allow for operation with +18dBu or +24dBu operating levels.


  • Ultra-clean SSL SuperAnalogue grade preamp
  • VHD system adds controllable 2nd or 3rd harmonic distortion
  • Switchable LF Filter (15Hz to 500Hz)
  • +48V Phantom Power with status LED
  • Pad for use with line-level source material
  • Front TRS Jack input with ultra Hi-Z switch for Instrument DI
  • Signal polarity invert switch
VHD Input Module
Physical
Depth200 mm (including front panel knobs, excluding connectors
-275 mm (including front panel knobs and connectors)
Height171 mm
Width35 mm (front/rear panels)
-49 mm (overall width (front and rear panels are offset))
Weight260 g
Boxed Weight460 g
EQ Filters
HF (Low Pass)20kHz – 3kHz (–3dB point) - 12dB/Octave
LF (High Pass)15Hz – 350Hz (–3dB point) - 18dB/Octave
Performance Specification
Microphone Amplifier Performance
GainContinously variable from +20dB to +70dB - Independently switchable 20dB Pad available
Input ImpedanceContinously variable from ≅1k2Ω to ≅10kΩ
Output Headroom> +26dBu at onset of clipping
THD + Noise(-18dBu applied, +28dB gain) - < 0.2% (20Hz - 20kHz)
Frequency Response20Hz to 20kHz - +0.3dB
-50kHz - -3dB
-150kHz - –3dB
Equivalent Input Noise(input terminated with 150Ω) - < –126dB at maximum gain
Common Mode Rejection(-10dBu applied, +30dB gain) - > 75dB from 50Hz to 1kHz
Line Input Performance
GainContinously variable from -24dB to +24dB
Input Impedance10KΩ
THD + Noise(-24dBu applied, +0dB gain) - < 0.05% from 20Hz to 20kHz
Frequency Response20Hz to 20kHz - +0.1dB from 20Hz to 20kHz
Equivalent Input Noise(Input terminated with 150Ω) - -90dB