F6 Parts Kit
There are two purchase options:
PCB and Transformer: Pair of mirrored F6 PCBs and 2 Jensen JT-123-FLPCH signal transformers ($119)
- Parts Kit: All of the above plus everything you need to stuff the PCB except the JFETs ($169)
Parts kit contents:
- Mirrored F6 PCBs (2)
- Jensen JT-123-FLPCH transformers (2)
- Q1/2 Matched IRFP240 MOSFETs (4)
- R1 .56R 3W (2)
- R2 .47R 3W (2)
- R3 100R 3W (2)
- R4 18R (2)
- R5 1k (2)
- R6 47k (2)
- R7/8/9/10 10k (8)
- R11/12 47R (4)
- R13 15k (2)
- C1/2 1000uf 25v (4)
- P1/2 5k (4)
- Z1/2 5.1v Zener (4) (Marked "31B")
- Z1a/2a 6.0V Zener (4) (Marked "33B")
- D1 LED (2)
The 4Ux300 Deluxe chassis is recommended for this amplifier. The 5Ux400 is overkill and the PCB placement of the transistors is non-ideal on the split heatsinks.
About the amplifier
These F-6 Clone Boards use the same circuit as the Nelson Pass / diyAudio FirstWatt F6 described in the diyAudio Firstwatt F6 thread. You will need to purchase the JFETs separately (matched LSJ74/LSK170 quad).
This set of circuit boards will make a MOSFET version of the F6 amplifier of Nelson Pass. This amplifier is a new and interesting development from his creative mind, where a small collection of parts comes together to make amazing, beautiful music. This creativity and solid engineering has kept Mr. Pass and his companies Pass Labs and FirstWatt at the forefront of specialist audio engineering and construction, where new and wonderful creations are made.
The original amplifier utilized extremely rare power JFET from SemiSouth, which will never be made again, and are all gone. Be warned, any eBay sources claiming to have the SemiSouth devices are fakes. If you happen to already have the power JFET, they can be used with this PCB.
Populate these boards with your components, then add your own power supply, chassis and heat sinks to complete the amplifier.
The F6 is a Class-A MOSFET power amplifier, with a JFET driver stage. It utilizes a small-signal transformer for phase inversion, so both the output MOSFET are N-channel. This transformer greatly contributes to the overall sonic character of the amp which is very highly regarded and considered to be similar and having all the benefits and positive characteristics of a tube amp... making some observers speculate that much of the positive 'tube amp' sound is the transformers, not the tubes. The F6 is a regular kind of amp - a voltage source amplifier, requiring nothing out of the ordinary from the preamp or the speakers.
As with most of the FirstWatt amplifiers the power output is 25WPC into 8 ohm. More into 4 ohm.
A bipolar power supply of (+/- 24V) is required. This will require an 18V+18V (or 36V Center Tapped) transformer from 300-400VA, (shielded transformers are preferred) and PSU capacitance of at 60,000uF per rail or more. A PSU for the F4, F5, or similar will be appropriate. See the build guide for details.
Chassis (heatsink) requirements
The 4U 'Jack of all Chassis' is ideal for this amplifier. If making your own chassis a good rule of thumb is at least 25sq inch (160sq cm) of finned heatsink per output transistor. (More is always better.) The diyAudio "Universal Mounting Spec" (UMS) is a common mounting pattern between the amplifier PCB and the heatsinks. If you utilize the UMS on your heatsinks or use one of the pre-drilled chassis from diyAudio, you will be able to quickly and easily mount different amplifier boards in the same chassis. For example, a 4U 'Jack of all Chassis' with a 400VA, 18V+18V transformer and PSU board, will give you a power supply and chassis where you could try the F4, F5, F5C, Aleph J, and other Pass/FirsWatt amps in the future merely by swapping the amp PCB. The investment in Chassis and PSU needs only be made once.
An Illustrated build guide showing all sorts of useful information on how to build the F6 can be found here - Build Guide
Great amp! So happy to have it - sounds just beautiful! Build is very straight-forward, even for newbies like me (have previously built only WHAMMY preamp). Patience and double checking is the key. Only thing which confused me is no marking for positive LED side on the PCB's silk-screen. Firstly, I have soldered it as LED's minus to the GND on both channels, but it appeared that left channel is driven from the negative rail (guys from forum responded within an hour-two!), so LED should be soldered in opposite (+ to the GND). 300VA audio grade shielded transformer from TOROIDY works very well - no hum. 600 mV offset in Deluxe 4u chassis gives just a bit less temperature than suggested maximum. It runs hot, but stable within months. F6 works with Troels Gravesen's Discovery 861 DIY speakers (92 dB efficient) which were built together with the amp. They work incredibly well together. Bass is deep, detailed and extremely controlled. Mids are full of body and details. Highs - just blew my mind! So airy, clear and detailed. But no fatigue whatsoever - can listen for hours and hours! It was a long way, but result totally worth it!
Kit is awesome, many thanks to the DIY Store, DIY community and our hero - Mr. Nelson!
after a long time my f6 is finally built and fully functional. the sound is fantastic, used in biamp for the mid-highs it is extremely dynamic and transparent. Really a good power amp in pure Class A.
This is my first power amplifier build and simply it is one of the best hobby projects that I ever had.
Thanks to 6L6 on well documented illustrated building guide and later on all useful recommendations and answers on F6 building forum.
For the novice, stick to the building guide step by step and you can't go wrong. I wouldn't say that it is easy cause you must have some basic knowledge about electronics, soldering and you need time and lot of patience, but this is right place to start.
Other than that, DIYAUDIO proved to be excellent service provider with top quality parts and service desk.
I will put my observations and possible improvements for more easier builds:
1.) Include Matched JFETs (Toshiba 2SK170/2SJ74 Quad Idss 8-11mA) in drop down menu for F6 clone kit.
2.) Include Matched MOSFET in drop down menu for F6 clone kit.
3.) I’m wondering if the chassis for the F6 could be deeper (e.g., 400 mm) and consequently have more space and better cooling. I have used recommended Deluxe 4U.
4.) Be careful with the 3296 Trimmer Potentiometer. It caused me a lot of trouble. Take care of it for good soldering and later during BIAS adjustment procedure.
Now I'm enjoying in my first F6 build. The sound is pleasant, warm and you can listen to the music for hours. Thank you, Mr. Pass, and 6L6 once again.
I have already started another DIY project with Nutube Korg B1 preamplifier. See you soon.
Good luck to all DIYers!
My F6 is running since several month. It's a great amplifier, fine and dynamic. I used an Hiraga 30W power supply used (capacitor bank 1.2F) with double C power transformer made by Dissident Audio (DB226) .
Received my F6 kit packed very well. Haven’t gotten too far along yet.I’ll probably need some more information before I go much further. Just received my Jfets also. I’m fairly new to the diy audio game, having previously built a beautiful sounding kt88 amplifier to which I’ve attached my recently completed Pass Nutube preamp. Very happy with everything so far and I am enjoying my rediscovered love of sound and electronics.
Fast delivery, top quality parts. Sound amazing, very easy to build and adjustments. Thank you 6l6.
Excellent reliable and fast service by diyaudiostore. The boards are first class quality. The sound is never fatiguing with my Oscar Heil Kitharas and my Luxman tube pre.
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