The TD-100 instrument preamp and tube direct box from Summit Audio features a hybrid signal path utilizing both a discrete solid state output device and a 12AX7A/ECC83 vacuum tube. Musical instruments take on the clarity of class A sound with the richness and warmth of vacuum tubes.
 
Perfect for both live and studio use, the unit offers XLR microphone level and 1/4" TRS line level outputs, plus variable input impedance, polarity switch, ground lift, signal and overdrive LEDs and a headphone output for use as a practice device. The variable input impedance control (loading) can dramatically alter the sound of an instrument. By lowering the impedance on the TD-100 the instrument's pickups get loaded down, changing their tone and the way they react to the string vibrations, generally making the tone darker and quieter.  Raising the impedance allows the pickups to work without hindrance, opening up the sound with a slight increase in gain. The instrument can then sit properly in a mix without EQ or other tone shapers. This effect works best with passive pickups.  The transformerless vacuum tube based circuitry isn't made to distort, rather it's used to add a subtle texture and smoothness, a professional sheen to an instrument. All of this functionality is packed into a very compact 1U half rack chassis with an internal power supply.