Fairfax

Class A Output Stage Drive

Fairfax began as an engineering experiment, initially inspired by the original Garnet Amplifiers Herzog® tube drive unit designed for Randy Bachman in 1965. Our analog guys decided to try and recreate all of the critical elements of a custom Champ-like tube amp circuit fully in the analog domain, but small enough to fit into a pedal enclosure (so it couldn’t use real tubes or an output transformer).

The final design features a cleverly miniaturized tube preamp, Class A power amp and an ingenious custom circuit that emulates the saturation characteristics of the output transformer (which is absolutely vital to get the sound right).

There’s even a variable Sag circuit that behaves just like a real tube amp does. At low Sag values the behavior is mild and only slightly compressed, and at max values the JFETs can go crazy and unbias — which gates the signal — leading to spitting and chortling sounds more commonly associated with fuzzes.

In order for Fairfax to behave like a real amplifier it needed a massive amount of operating voltage, so a transformer-based power supply converts the 9VDC input voltage to 40V internally. This gives Fairfax the power that it needs for high headroom and amp-like feel, allowing for a wide range of tones.

At lower Gain settings Fairfax can be sweet, gently pushing the input to your amp with additional harmonic richness, a touch of saturation and a flat frequency response. At higher Gain levels the sound becomes fully saturated, and that large range of gain on tap allows Fairfax to be used in nearly any setup imaginable.