General Overview

The hamptone LCMP is a tube microphone preamplifier that was introduced in TapeOp magazine although Scott Hampton does sell updated versions of this kit now. The circuit is a basic tube amplifier design with a two stage self-bias class-A design using 6072A tubes on the input and a cascode follower output stage utilizing a 12AU7. The inputs are transformer balanced and required assembly of a mu metal shield to eliminate noise. The input transformer is a custom design but very nearly matches a Jensen 110K. The output stage is also transformer balanced. A direct injection (DI) input bypasses the input transformer.

The power supply uses a regulated heater element design and a simple transistor regulation circuit for the B+ supply. Phantom power is fully regulated. The supply uses a toroid transformer to limit the amount of AC induced noise in the preamplifier and the tube stages are located in a separated section of the chassis to also help reduce noise.