First Watt F4 Operation And Service Manual

First Watt model F4
Operation and Service Manual
Introduction
Anyone paying attention is aware that First Watt makes unusual amplifiers with
the emphasis on performance at low power levels.
Here's another one.
The F4 is Class A impedance converting amplifier, having no voltage gain or
feedback. Its input impedance is 48,000 ohms, and its output impedance is about
0.2 ohms. It is suitable for driving a high sensitivity loudspeaker with the output
voltage of a preamp or other line-level audio source. It is also useful with a less
sensitive loudspeaker in a bi-amped configuration where it takes input from the
output of a conventional amplifier.
As a stereo amplifier with single-ended inputs and outputs, it will deliver up to 25
watts into 8 ohms with a damping factor of 40. It will do 50 watts into 4 ohms, and
as a mono-block amplifier with parallel inputs and outputs, it will do 100 watts into
2 ohms.
As a mono-block amplifier with balanced inputs and outputs the power output
rating is 100 watts into 8 ohms at 0.5%, and the damping factor is 20.
nd
At ordinary listening levels the amplifier operates Class A, and the distortion is 2
harmonic in character, rising or declining in linear proportion to the output power.
The amplifier has a direct coupled input and output, with a -0.5 dB rolloff around
.1 Hz and 200 KHz, and it does a clean square wave at 100 KHz.
The combination of a simple Class A circuit operated without feedback and the
excellent objective performance gives us a superb sounding amplifier. The low
distortion, bandwidth extension, and high damping results in midrange clarity,
treble detail, and control on the bottom end.
While these are available from most good solid state amplifiers, the F4 also brings
depth, imaging, midrange warmth and top end sweetness.
Overall, it is one of the best sounding amplifiers, and if you can live with unity
voltage gain in your amplifier, it is possibly your best choice.