This one may look like your traditional 2203 Master Volume head but it is in fact the last incarnation of the Marshall Superbass. While the first models use to be very close to the 1959 Superlead models, they evolved during the seventies to include a lower gain preamp and a baxandall tone circuit. This particular model employs this design with the added benefit of a semi parametric mids control and a “slope” control to dip the mids.
Its tone is fairly flat and dark with a medium content that’s stronger than most bass amps. The “slope” control isn’t particularly progressive or effective and the 100W power rating may not be enough in some contexts. The result isn’t too bad for bass but the strong competition of the eighties in the bass amp camp meant the end of the Superbass range when the JCM900 models arrived on the market. Apart from the VBA400, Marshall hasn’t put out a powerful and straightforward valve bass amp since then. Maybe its time they did?