The Studio Projects VTB-1 is single channel low cost microphone preamplifier, incorporating true class A/B switching. The unit is perfect for the professional and home project studio doing production, broadcast and voice over work.
A "Tube Drive" control allows the user to blend as little or as much of the 12AX7 tube circuitry as required. The VTB-1 can go from a pristine solid state sound, to any combination of Tube Drive, including hard distortion for guitars and bass.
- Microphone Preamp
- Vocal microphone preamp with warm transparent character that doubles as a Tube DI Box. Discreet, current-source fed, paralleled-transistor balanced input stage feeds a bipolar opamp balanced-unbalanced converter. A dual feedback design provides for low distortion performance while a two stage design provides up to 45dB gain with the second stage contributing up to 15dB gain.
- Line Input
- FET-input opamp buffer with hi-input impedance to avoid pickup loading when used as an instrument preamp. Second stage provides adjustable gain from 10dB to 30dB with constant hi-impedance maintained.
- Hi-pass Filter
- 75Hz, 3-pole -18dB/oct high-pass filter for low-frequency wind and rumble elimination.
- Tube Blend
- Constant-level blend control allows the user to smoothly change from an all solid-state path to a tube-based preamp. This allows the user to add the desired amount of tube sound to the signal without having to deal with complicated "tube drive" controls and such. Alternately, it allows the user to use only the solid-state portion of the preamp to get a very low distortion, un-colored sound when desired.
- Tube Stage
- 12AX7 vacuum tube with a DC filament supply for minimum hum and noise. First half of the tube is operated as a high-gain amplifier stage while the second half operates as a cathode follower to minimize loading of the first stage. A low-voltage plate supply is used to create a "starved-tube" condition for enhanced sound.
- Output Stage
- Bipolar, lo-noise, high output-current opamp used for best performance. The first stage is used to provide 6dB of additional gain and drives the line out jack and pin-2 of the balanced out. The second stage provides signal inversion and drive for pin-3 of the balanced output, effectively providing an additional 6dB of gain.