First Watt F4 - Nelson Pass Labs

First Watt the F4 is a unique amplifier. It has no feedback and no voltage gain, only current gain.

The first watt is the most important watt. Nelson Pass has spent his life making it sound beautiful.

The F4 is Class A impedance converting amplifier. Its input impedance is 47,000 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 about 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 1%.

The amplifier operates Class A to 25 watts (50 peak), and the distortion is 2nd and 3rd harmonic in character, rising or declining in 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. It does a clean square wave at 100 Khz.

Available as a Monoblock pair or individually. Both these amps were made by the expert hands of Nelson Pass.

Here’s a great review of this amp - https://www.6moons.com/audioreviews/firstwatt6/f4.html

They come with original packaging. No longer available - these are part of audio history and very rare on the open market today.

New they were approx €3000 and have increased in value in recent years. Amps in perfect condition.

Available individually for 40 000 nok or 65 000 nok for the pair.