Basic Bipolar Booster

A single transistor gain stage is useful to provide a voltage boost to low level guitar signals, not only to make the sound louder but also to provide a powerful signal to overdrive the tubes in a guitar amplifier. The simple common-emitter amplifier is a basic circuit that has been used in dozens of effects pedal designs.

The circuit to the left is exactly like the vintage LPB1 (or LPB2) boosters sold by Electro-Harmonix. The E-H Screaming Tree (or Screaming Bird) was the same layout with components changed to provide a treble boost. The Ego Booster was a microphone amplifier using the identical 8-component circuit and the exact same configuration has been adapted by boutique pedalmakers and used in numerous custom booster pedals. Even the vintage Rangemaster is a variation of this versatile circuit.

This project can be built on the AMZ etched and drilled Multi-Purpose Transistor printed circuit boards are ready-to-solder and will fit in a 1590B hammond diecast box. The boards are 0.062" thick FR4 material, two-layer construction with tin finish over 1 oz. copper and plated through holes. They are sized (1.3" x 1.5") to fit in the typical Hammond 1590B or similar box and have a mounting hole already drilled. Included with each board is a printed sheet with schematics, parts layout and suggested mods.

The same AMZ circuit board can alternately be used to make a jfet booster pedal or a mosfet booster. (Only one booster at a time can be assembled on each circuit board.) When you purchase one of the boards, you will be emailed a link to a confidential web site with numerous mods and the instructions on how to use the board with jfets or mosfets. The web page also has some photos to help you with construction.

The Multi-Purpose Transistor pcb is available on the AMZ ordering page.