The new First Watt F8 power amplifier has been created as an updated version of the earlier J2 amplifier, introduced in 2009.

Like all First Watt designs, it is a relatively low power at 25W/channel into 8-ohms, simple Class A circuit, designed with a low parts count. It is the 21st product from First Watt, since its founding in 1998 as Nelson Pass’ “personal laboratory”.

Nelson Pass’ First Watt F8 Amp

Nelson Pass

Nelson explains First Watt: “I spend a lot of time building and evaluating basic amplifier concepts with an eye toward producing the highest quality sound with elegantly simple circuits. There is no such thing as a perfect amplifier, but there is a best amplifier for each type of speaker, music, and listener. Each First Watt model is a unique design and is ‘best’ in some particular way. They look alike because they all use the same basic chassis and power transformer. On the upside, it makes it easy for me to test ideas and compare different designs with the hardware being a fixed constant”.

First Watt J2

Nelson continues: “The J2 is perhaps the most popular amplifier made by First Watt. Brought to market eleven years ago, it was not intended for more than our usual 100 unit total production.  However, it was so well received that I broke my rule and it is still made.  Still, there will be an end, as the special transistors needed have long since been unavailable and our supply is starting to run low. I wanted to create yet another amplifier with the SemiSouth SiC R100 power Jfets, so in 2015 I developed a design with the same output stage but an alternative front end circuit. The prototype was clearly an improvement, but the J2 remained so popular that we decided to wait. As the years went by, I put some more work into it, and now finally releasing it as the F8.”

The Simplified Schematic

There are two Common-Source gain stages, consisting of Q1 and Q2, both set to their operating points by current source Q3. Q1 is the Toshiba 2SJ74 Jfet, and Q2 is the SemiSouth Silicon Carbide R100 power Jfet, both parts NOS from the First Watt vault.  Q3 is the venerable International Rectifier workhorse, IRFP240

First Watt F8 Schematic

Nelson says of his new First Watt amp: “You will have noticed, I enjoy amplifiers with a little personality. They don’t have to measure perfectly, they just have to sound good. This is a simple little Class A amplifier with a very nice personality, and I hope you like it.”

Specifications

Distortion @ 1 watt, 8 ohms:  0.02%

Input Impedance:  100 Kohm

Gain:  15 dB

Input Sensitivity (1 watt):  0.5 V

Input Sensitivity (max output): 2.7 V

Damping Factor:  38 @ 8 OHMS

Output power 8 ohms:  25 watts @ 1% THD, 1KHz

Output power 4 ohms:  13 watts @ 1% THD, 1KHz

Frequency response:  -0.5 dB @ 10 Hz, 200 KHz

Noise:  <100 uV unweighted, 20-20 KHz

Power consumption:  170 watts

Fuse:  3AG slow blow type – 2.5 Amp for 120 VAC / 1.25 Amp for 240 VAC

Price

USMSRP: $4,000. Shipping now

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