Guitar PreAmp: Tech 21 SansAmp PSA-1 The best sound among the available non-tube pre-amps. Stores 98 MIDI-switchable presets. Very easy to edit & store. Exceptionally good tone. The device is a pre-amp which emulates various tube amplifiers (e.g., Fender, Marshall, Mesa), both in their pre-amp and power amp characteristics. Even tube enthusiasts are stunned to discover that the PSA-1 has no tubes.