Used Alembic F-1X
The F-1X is regarded is one of the best bass preamps ever built. This one looks almost brand new. Alembic is a legendary bass manufacturer and has developed some of the most innovative bass related electronics and sound reinforcement technology in over 40 years of business.
The F-1X gives you a unity-gain impedance matching amplifier to feed guitar-level effects units. The effects return goes thru the tube gain stage and then to the tone controls. The signal from the tone controls is amplified and sent to the full-range output jack on the rear panel. This same signal is also fed to the crossover network. A transformer-isolated output feeds a 3-pin Cannon jack.
Two input jacks provide the same functionality as found on the F-2B preamplifier. The input is buffered by a cathode follower tube circuit, which is a unity-gain impedance matching amplifier to feed the guitar level effects loop. This gives minimum loading on the output signal from the guitar while driving the effects loop gear with the same signal voltage level as the guitar but at a lower impedance, to isolate cable and other loading effects from the guitar pickups.
The other half of the 12AX7 tube provides the preamp's gain. This gain comes before the volume control and the 300 volt supply assures that even large transients are handled without overload or distortion. The tone controls are the interacting Fender circuit. The bright switch shunts high frequencies around the volume control. The deep switch changes a capacitor value in the bass control to change the frequency response (and a second section on the deep switch changes the gain of the following amplifier to compensate for the resulting change in signal level).