F4 Monoblocks-"Special Edition" (DIY)

About the F4 Monoblocks-"Special Edition" (DIY)

The First Watt F4 is a unique Class A amplifier designed by Nelson Pass, operating as an impedance converting amplifier or power buffer with no voltage gain or feedback. It features an input impedance of 47,000 ohms and an output impedance of about 0.2 ohms. The amplifier is suitable for driving high sensitivity loudspeakers directly from a preamp or line-level source, or for use in bi-amped systems with less sensitive speakers. In stereo mode with single-ended inputs and outputs, it delivers up to 25 watts into 8 ohms and 50 watts into 4 ohms. In mono-block mode with parallel inputs and outputs, it can deliver about 100 watts into 2 ohms. With balanced inputs and outputs in mono mode, it provides 100 watts into 8 ohms at 1% distortion. The amplifier operates in pure Class A up to 25 watts (50 watts peak) with low distortion characterized by 2nd and 3rd harmonics. It has a direct coupled input and output with a frequency response from approximately 0.1 Hz to 200 kHz and a damping factor of 20 to 40 depending on configuration. The F4 is praised for its midrange clarity, treble detail, control on bass, depth, imaging, midrange warmth, and top-end sweetness. It is often used by audiophiles who appreciate its minimal signal manipulation and purity of sound. The "Special Edition" DIY version is built using quality PCBs and chassis available from DIY audio suppliers, with detailed build guides available online. The amplifier is no longer in regular production but can be found as used or DIY kits.