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F1 or F1J Amp and Power Supply Boards with UMS Mounting Pattern Group Buy

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#21
The payment window for the group buy closed yesterday, thanks to everyone for the prompt payments and good communication. If anyone else is interested, there will be some extra boards, just PM me.

Good news for those who have paid for boards! The number of interested parties stabilized about two weeks ago so I ordered the number of required boards (with a few extras) and they arrived last Friday. I have built up one amp channel to validate the new boards and it worked great. The extra potentiometer made it very easy to dial in the DC offset to ~2mV.

I am waiting for shipping materials to arrive and will start sending boards out later this week.

The picture below is an F1J test build of the new boards. My previous F1 has a bit more bass than desired, so I wanted to play with the input cap value on this build to reduce the bass a bit. The full recommended value for the F1J is 11uF. I started with the 3uF caps shown and also tried 4.0uF, and 5.6uF. 3.0uF and 4.0uF were noticeably shy on bass, 5.6 uF was pretty good, and I suspect 6.8uF would also be good and is where I will likely end up.
 

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#22
Thanks for the update Chas, nice to hear it works. Can you post your as built and tested schematic and BOM when you are finished thanks.

Can I ask what type you are using for the larger 3watt resistors as shown in the posted photo?
 
#27
Very observant. 🙂 R127 and R128 are an option for adjusting DC offset. See post 198 in the Firstwatt F1J thread for more information. These resistors have not been populated in my picture because the amp needs to be powered up to determine what if any resistance is required. Depending on how well matched your transistors are you may not need anything there. I am working on an illustrated build guide as time permits, and will post an updated BOM and schematics in that thread as soon as it is ready.
 
#29
All international shipments are out. USPS is quite busy right now, so the Priority Mail envelopes for domestic shipping (ordered 12/2) have not been delivered yet. All orders have been pulled and packaged and are ready to go when the envelopes arrive. If you want your boards to ship ASAP let me know and I will make other arrangements.
 
#31
BOM and Schematics for the latest revision of the boards are attached. Changes to the BOM from the previous version highlighted in green and a note to the side that explains the change. The power supply schematic is a marked up version from the Firstwatt F1 service manual.
 

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#33
My boards arrived - really nice job!!! I have a chassis on hand for this, plus mosfets, and maybe a donut. This maybe a quick and easy project with ordering some caps and resistors.


I have done a big batch of IRFP9240 and IRFP240 matching end of 2020. If anyone who got F1/F1J boards needs matched MOSFETS, PM me what you need.
 
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