F4 Essentials
The essentials kit contains the PCBs along with all of the critical devices to complete two channels of the F4 amplifier including the rare JFETs.
- 2 x F4 Amplifier PCBs
- 6 x IRFP240
- 6 x IRFP9140
- 2 x TL-431
- 1 x Matched Quad of JFETs
Please note: Numbers on the MOSFETs are ID numbers only. They do not indicate measurement values.
The F4 is a Push-Pull, Class-A, MOSFET power amplifier. It is unique in that all of the active devices (transistors) are connected in a 'source-follower' configuration, which adds less coloration than many other arrangements.
It sounds great, and it is extremely versatile. Each channel can be used separately as a stereo amplifier, or they can be bridged or run in parallel for higher power into various loads.
The F4 can be paired with almost any normal speaker. However, for most people, the F4 needs a preamp that has voltage gain. In order to drive the F4 to it's maximum power output, a pre-amp with gain is needed. For reasonable listening levels and/or with sensitive speakers, many builders enjoy connecting their F4 directly to their source.
It can also be used on the output of a "flea-powered" tube power amp, keeping the tone of the tubes, but adding additional power for less-sensitive speakers and/or to add a little oomph to the lower registers where some tube designs might like a little help.
The sonic signature of the F4 is intended to be close to transparent.
Please read the First Watt F4 manual for more explanation on various configurations.
Power supply requirements
A bipolar power supply of (+/- 24V) is required. The PSUs for almost all First Watt amplifiers including the F4, F5, F6, M2x, Aleph J, and Aleph Jzm are identical. The same PSU can be used for all of them.
There are three PSUs to choose from:
- Nelson's Bipolar Power Supply is the least expensive and easiest to build. It was designed to compliment the beautifully simple and inexpensive "minimalist" F5m.
- The Simple Linear Bipolar Power Supply is the choice for DIYers that prefer a higher performance power supply, but enjoy the convenience of a full kit. For builders that prefer to choose their own parts, the PCBs are also available.
- The Universal Power Supply PCBs allow the experienced DIYer to choose every part of their PSU or use what they have in their spare parts bin.
Chassis suggestions
The 3U Deluxe is an excellent choice. For builders that want more space and/or may want to build a bigger amplifier in the future, the 4U Deluxe or 5U Deluxe are great choices. We also have a back panel parts kit to make life easier, and don’t forget the Keratherm.
Key Information
- Power Amplifier Project
- Designed by Nelson Pass
- Intermediate Difficulty
- Only Essentials Kit Available
- Basic Build Guide
Highlights
- No voltage gain
- Excellent for pairing with a "flea watt" tube amp
- Build two as monoblocks for bridged or parallel operation
Links, Discussion & Files
Well, you'd be surprised how much you might do with this no gain amplifier. You should read up on it and if it seems you'd like to give it a try you will be rewarded with a new and lovely perspective.
It will show you what you need to know about your preamp. It will show you how a speaker can be really controlled. I use mine to drive a pair of high efficiency sub woofers because of the control afforded. It is a great tool in making music and taking a full assessment of where your stereo is at. I have built the F4, F5t, F6 and the Aleph J, all very good experiences and all still in service but the one that taught me the most about stereos is the F4.
All of the kits here are a great bargain and very well made. The gift from Nelson Pass and his supporters is not to be passed up. Build this amp! You'll be educated and it'll be fun!
Great service and fast delivery, as always from the store.
Excellent quality boards. Fast delivery
F4 is a great sounding amp and a fairly straightforward build. Only issue I had was a slight mismatch in the Mosfets that showed up measuring bias across the 0.47 ohm resistors. No idea how common that is but fixing it required swapping two mosfets. If you have the ability to match test the mosfets before installing I suggest you do that otherwise you may have to desolder and reinstall them to get a better match. Also, strongly recommend using a 7-8K resistor for R9 instead of the 10K that is specified in the BOM. I wasn't able to bias one side high enough with that 10K resistor.
Excellent kit! My F4 works great! Thank you!
Excellent kit, service and delivery . Now working perfect in F4 .