My amp has been running for 5 full months now with daily use of 5 or 6 hours. It is truly impressive that the bias does not drift at all for both channels. And not a single unintended pop or other noise coming out ever. The only glitches were the 1.6A fuse (on 220V line) blew twice at switch on during this period. Now replaced with a 2A fuse. With such great sound coming from such simple circuit, the designer is really a master.
Have you got a thermistor in the primary side of the transformer? If not, it may help with the fuse blowing. See Post in thread 'F5m kit' https://www.diyaudio.com/community/threads/f5m-kit.408290/post-7620032.
The power supply boards are Nelson's Bipolar Power Supply. One board and one transformer per channel. The CL-60 & AC Cap PCBs are installed. One per channel. Now looking back, I should have replaced the 4700uF caps that came with the kit with 10000uF. Maybe after I finish the F5T I am working on.
After looking at this a little closer, I am intrigued by your use of those black little towers to attach cables to. That means that I have to come up with something cool like these.
You can download the 3D print files here for the wire management towers. I posted the 3D printed stuff I've designed and found useful for diyaudio under the parts threads.
Search "3D Print" posts by me.
Search "3D Print" posts by me.
Congratulations on you successful build.
You chassis looks pretty sleek - what are the dimensions of the heat sinks?
Hi
The heatsinks I'm not sure of right this second...but it's the 2025 deluxe 2U/400mm...forgot a pic with switch engaged and light on...daylight of course but the lighted switch is pretty subtle...and for what little I've let it run so far it's DEAD silent...no hum ,no hiss, no buzz, no noticeable on or off thump
Thanks for the help , pointers, and the kind comments everyone.
Cheers
Jody
The heatsinks I'm not sure of right this second...but it's the 2025 deluxe 2U/400mm...forgot a pic with switch engaged and light on...daylight of course but the lighted switch is pretty subtle...and for what little I've let it run so far it's DEAD silent...no hum ,no hiss, no buzz, no noticeable on or off thump
Thanks for the help , pointers, and the kind comments everyone.
Cheers
Jody
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What Nelson did here for the DIY community is unbelievable. So simple a design with one resistor in the signal path, but... the measurements are crazy good. That very slight reduction in gain above 10kHz or so is just perfect, the distortion vs. frequency dependency is almost flat (!! unbelievable !!), and an increase in distortion vs power output even against 4 ohm loads is stunning - minimal, linear. This amp will keep its special character up to its full power regardless of the load connected to it OR the frequency. Then, he gives the compact design for both PCBs as well, preventing wiring/grounding errors.
@birdbox a note of appreciation to Dan aka BB. Sticker applied to the business end. Your instructions were crucial to success, one of the more fiddly tasks but totally worth the outcome 
Looks really good on that brushed steel plate! Nice work.
I have 3 more in that silver color and one in black if anyone wants one (continental US only please due to shipping).
I have 3 more in that silver color and one in black if anyone wants one (continental US only please due to shipping).
I could finish one of the channels using 2SJ201/1530 FETs and the rest of the parts including PSU from the store. Using 0.22/5W biasing resistors so I set the bias to 0.33vdc so around 1.4A current. My sinks are huge 300/200/75mm mono blocs, so using single FET on each sink 🙂
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Listening to the single channel with my PAP clone speakers which are 4Ohm impedence paired with HPA1 clone preamp and Aya5 dac I had to increase the volume significantly to get decent gain. Maybe I am biased as my existing AN39 amp built for 4R does the same gain with less than half the volume pot. Also I will increase the bias to 1.5A as my sinks are just warm even after an hour of play, so lots of room for heat.
Not sure if I need to use FE22 preamp with 13db gain instead of HPA1 but will try that over the weekend to see how it turns out. But initial impression is that its a bit on the warmer side and laid back sound signature especially with PAP.
Thanks
Not sure if I need to use FE22 preamp with 13db gain instead of HPA1 but will try that over the weekend to see how it turns out. But initial impression is that its a bit on the warmer side and laid back sound signature especially with PAP.
Thanks
Here is my F5m in a 4U Mini Dissipante chassis from Modushop. The first time powering it up the dim bulb slightly glowed for a few seconds. This amp is dead silent, you could not tell its on if I hadn’t added a few LED’s! Biased it at 0.68V / 1.45A after many listening tests. The heatsinks are at 55C after 1 hour warmup.
It sounds glorious, powerful bass, clear highs and mids, but the amazing thing is how clear the background sounds come through. It goes extremely loud using the Klipsch RP-600m speakers. I can’t thank Nelson Pass enough for sharing his design and knowledge! After building two ACA Mini’s I had the confidence to build the F5m. I wanted to learn more about how amplifiers work an these projects helped me reach that goal. Also thanks to all members who shared their build experiences and thoughts.
It sounds glorious, powerful bass, clear highs and mids, but the amazing thing is how clear the background sounds come through. It goes extremely loud using the Klipsch RP-600m speakers. I can’t thank Nelson Pass enough for sharing his design and knowledge! After building two ACA Mini’s I had the confidence to build the F5m. I wanted to learn more about how amplifiers work an these projects helped me reach that goal. Also thanks to all members who shared their build experiences and thoughts.
