Vectronics VEC-1680K - Manual (Page 20)

VEC-1680K Owner’s Manual Vacuum Tube Preamp
20
OPERATING INSTRUCTIONS
Set-up of the VEC-1680K is pretty intuitive. Like most in-line instrument
accessories, the instrument connects to one end--and the power amp connects to
the other! The following diagram shows how to make these connections:
Foot Switch
Input Power
Output
Gain Output
Power
Adapter
Foot Switch
Instrument
Power Amplifier
VEC-1680K
Foot Switch: To bring the preamp on-line, simply close the foot switch. The
internal relay re-routes the audio path through the preamp circuitry. To bypass
the preamp, open the foot switch.
Gain Control: The first pre-amp stage runs wide open, with no manual gain
control or negative feedback. This boosts the audio signal, but introduces little
compression or distortion. The output then passes through the Gain control and
into the second preamp stage. Unlike the first stage, the second stage can be
overdriven easily because the signal coming into it is much stronger. The Gain
knob regulates how much stronger. Drive the stage lightly, and you'll get Mark
Knoffler bell-like clarity. Drive it harder, and you'll get increasing increments of
Stevie Ray Vaughan fullness and grit! Crank it way up, and you'll get a taste of
Jimi Hendrix!
Output: After the preamp's second stage, a fixed attenuator knocks the signal
back down to "guitar" level. The Output control then provides added gain
reduction to set the correct drive level for your particular power amp. For best
results, always set the Output control so that it approximates the "bypass"
volume level. This ensures that any tonal coloring of your instrument's sound
occurs in the second stage of the 12AX7 tube--and not because your preamp is
overdriving the transistors in your power amp!
IN CASE OF DIFFICULTY
Before seeking assistance, check below for a possible solution: