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).
A solid state circuit restores the signal level after the volume control and provides impedance matching to drive the full range output jack on the rear panel. Additionally, it drives the crossover network. The active crossover network provides 12 dB/Oct slopes to divide the output for bi-amping. The crossover points occurr at 6 dB down so that the acoustic signals from the loudspeakers add seamlessly. A front panel control trims the high-frequency signal component to match the level of the low frequency output.
A transformer-isolated balanced output to an XLR type connector provides auxiliary Recording or PA feed. A switch selects the source to be the effects return (Pre) or the full range output (Post). The transformer is large enough to handle the low-frequencies without distortion to give good clear lows and a resistive pad isolates the transformer from loading effects of long cables to give clear highs.
The heater of the 12AX7 tube is supplied by a regulated direct current supply to assure low hum. The AC Line (Mains) connection is an IEC (computer-type) detachable cord. The supply voltage can be changed by moving jumpers inside the unit to operate from 100, 120, 220, and 240 volts for operation anywhere in the world. The F-1X is housed in a sturdy, road worthy, steel enclosure.
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