Musicans and audio people tend to go through a progression.  First they are fascinated with musical instruments.  Next they are fascinated with microphones.  But eventually they become fascinated with preamps.  It sounds like it should be a very minor accessory, something like a cup holder on an SUV, but over time one comes to realize that the preamp may be the determining factor in how your music sounds, whether you are playing live or recording, or just building a great stereo system.

A confusing array of preamps are available running from under $100 to many thousands of dollars.  The factor I was really looking for in a preamp (which many musicians look for) is referred to as “warmth”.  This is an imperfection (referred to by engineers as a “nonlinearity”) that was common in early tube-based audio equipment.  This imperfection tended to make louder sounds harmonically richer (adding even-order harmonics), and made them be less different in volume from the quieter sounds.  Eventually, engineers built chips (called operational amplifiers) that did not have this imperfection (our engineer would say they are perfectly linear), but when people heard the new perfect sound, it did not please them.  They said it was “cold” and lacking the warmth of tubes. 

This led to a fetish for vintage equipment from the era before the new chips started being used.  But equipment does not have to be vintage to have the warmth that makes it pleasing to the ear.  It also does not have to have tubes in order to have warmth.  There is a type of transistor called a FET (field effect transistor) that has a similar nonlinearity to what preamp tubes have.  With all this in mind, I decided to create my perfect preamp.

This week I built the first model for actual use.  There were lots of prototypes over the last year, and I created a couple of different printed circuit boards along the way.  The preamp has two channels, and each channel has three stages.  The first stage has a FET transistor, the second stage has tone controls, mimicking those on a Fender Twin Reverb guitar amplifier, and the third stage is a gain stage that uses one of those operational amplifier chips, which will perfectly reproduce the warm sound of the FETs.

Below are pictures of the preamp.  I have used it with my Chapman Stick, electronic keyboards, and a Taylor acoustic guitar (with a mic and a piezo pickup) with good results on all of them.

Preamp Front

Gloster Preamp Open

Gloster Preamp Circuit Board