SSL VHD+ Preamp - 500 Series The SSL VHD+ is a 500 series preamp module found in the SSL Duality. The VHD+ is an immensely versatile preamp with the ability to deliver ultra clean SSL Super Analogue grade recording, but also colourful recordings via the patented Variable Harmonic Drive. The BHD system uses a 100% analogue signal path to generate rich harmonic distortion. Increase VHD input gain and 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 transistoresque grunge. The VHD+ Pre module gives the user ultimate versatility from a studio grade preamp. Whether it's ultra-clean traditional SSL, subtle warming or totally trashy transistor distortion, VHD will change your expectations of what a preamplifier should deliver. Gain Controls The red pot provides up to +75 dB of gain, whilst the black pot provides a variable mix of 2nd to 3rd order harmonics (once the VHD-IN switch is engaged). The grey pot provides +/- 20dB of trim. Use this to control the output when driving the VHD preamplifier circuit. High Pass Filter The High Pass Filter section is a switchable 18dB/Octave variable filter. See the block diagram for the position in the circuit. Line In/DI Jack Socket 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 a -10dB level pad to allow for typically louder balanced line level signals. The Jack input can also be used with unbalanced (TS) cables. 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 Input Impedances 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 XLR input impedance changes from 1.2 KΩ to 10KΩ and the front panel Jack changes from 10KΩ to 1MΩ Switch Functions 48v - Applies phantom power to the rear XLR input, a tell tale red LED indicates phantom power is active. PAD - Applies 20 dB of attenuation before the signal enters the preamplifier. HI-Z - Switches the XLR Mic preamplifier impedance from 1.2 KΩ to 10KΩ or the front panel Jack from 10KΩ to 1MΩ Ø - Polarity switch inverts the polarity of the signal by 180°. Key features SSL SuperAnalogueTM grade preamp 2nd order harmonics (valve warmth to extreme distortion) 3rd order harmonics (transistor edge to totally trashed) Absolute control via 2nd and 3rd order harmonic blend Variable Harmonic Drive (VHD) in/out switch Switch-able LF Filter +48V phantom power Phase invert switch PAD switch Hi-Z switch
