Direct box employing hybrid vacuum tube and solid state circuitry

DETAILED DESCRIPTION I claim: 1.
A circuit for coupling a high impedance audio source to a low impedance audio destination, comprising: at least one operational amplifier with first and second input ports of opposite polarity and with an output port and having a feedback loop to establish the gain of said operational amplifier; at least one vacuum tube with cathode, plate and grid; the grid of said vacuum tube being coupled to the operational amplifier output port; an input terminal for coupling to said high impedance audio source and an output terminal for coupling to said low impedance audio destination; said input terminal being coupled to said first input port of said operational amplifier, and the output terminal being coupled to the cathode of said vacuum tube; feedback means coupled between the cathode of said vacuum tube and the second input port of said operational amplifier thereby placing said vacuum tube in the feedback loop of said operational amplifier; wherein said feedback means is of a preselected impedance sufficient to cause sonic effects of said vacuum tube to be imported onto sound of an audio signal transmitted through said circuit from input terminal to output terminal.
2.
The circuit of claim 1 wherein said grid of said vacuum tube and said output port of said operational amplifier are direct coupled to one another.
3.
A circuit for coupling a high impedance audio source to a low impedance audio destination, comprising: at least one operational amplifier with first and second input ports of opposite polarity and with an output port and having a feedback loop to establish the gain of said operational amplifier; at least one vacuum tube with cathode, plate and grid; the grid of said vacuum tube being coupled to the operational amplifier output port; an input terminal for coupling to said high impedance audio source and an output terminal for coupling to said low impedance audio destination; said input terminal being coupled to said first input port of said operational amplifier, and the output terminal being coupled to the cathode of said vacuum tube; feedback means coupled between the cathode of said vacuum tube and the second input port of said operational amplifier thereby placing said vacuum tube in the feedback loop of said operational amplifier; further comprising direct current power supply and wherein said vacuum tube and said operational amplifier share said direct current power supply