F5 made by a complete dummy

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The title says it all. I want to give my experience to the ones who wouldn't dare trying this built.
As mentioned, my electronic knowledge is nil ...as my cash flow. But I am a music lover and wanted a real class A amp. So the only way to get it was to built it.
It happens FirstWatt philosophy strike my understanding, simple schematic and if the first watt isn't good don't add more.

Among the different FW amps proposed by DIY, I had to make a choice so I define clearly what I was after and the very helpful peoples of this forum guided me forward the F5. I mean Jim (6L6) and Nelson himself, what better advisers could I get ? Then the fact that the board have no condenser, ensuring a very long life span, basked me.

I read during days and nights the forum, went to basic theory on internet getting just enough understanding because I had no intention to become proficient as I have no particular interest in electronic theory and do not plan to be an hobbyist.
That was hard because of the many acronyms used. I had to figure out what they stand for, translate into my own language and understand what it is, what it does etc...
I also refrain from asking as much as I could, you memorize better when you search.

On the practice side of thing, I bought the necessary tools which are often advised in the forum discussions. Oh! The list is impressive....just a soldering iron and desoldering iron ! I had two cheap voltmeters already and the ordinary small pliers. But Mark mentioned somewhere a 10$ tester. It took two weeks to come from China, arrived broken but was immediately replaced.

I went to YouTube for soldering lessons, took an old PCB and started to practice, desolder, resolder etc...
I bought the ACA kit first to see how things could go. It went like a charm, switch on, set the bias, listen, enjoy, great, I felt confident.
But when you are like me, don't try to be funny and clever, just follow wisely what is advised in the original project, go slowly and carefully, be organized. Get to something only when you are sure to understand it.

For the F5 boards, there was no particular difficulties, the spares being part of the kit, you just have to chose the LED, find its resistor if you want to have some indication of the power being on for each channel. I took few bad experiences from people on the forums for granted and apply the solutions given.
The biggest problem was the PSU, understand roughly how it works and get the spares. No point to get the F5 PCBs and components before I solve this problem. It took me a long time because when you read the threads on the forum, you are bounced from one point to another which has nothing to see with what you looking for but is interesting for some others matters you may have under looked.
You get lost easily, you don't know after a while where you stand. You may read and stay in the dark a bunch of times, you doubt, then a sudden phrase you have missed until now switches on the light.

I scrutinized the pictures, the schematic, the BOM lists.

So here is what I did :
- I bought everything I could from DIY store, it simplify things a lot, the F5 boards come complete with components, except for the led and its resistor.
- The PSU board was tricky because it is a general purpose board. If you are using "rectifiers", you don't need the "diodes" part , so you have to cut it off. Do that carefully with a cutter and a ruler, be patient, don't force on the cutter to avoid slippage. The rectifier solution is the easiest from far and it save space. The reference is Vishay Bridge rectifierGBPC3510A.
- I bought the PSU components and all what I could from Mouser, they have nearly everything
- I decided not have any LED on the PSU board, I don't see any use for it except put some light into the box.
- I displace the LED off the F5 boards to the front plate, where I asked the chassis provider Modushop (hi-fi 2000) to drill two holes, very much like the ACA. So you know the two channels are powered on. I chose 5mm leds of 3w and I had a hard time finding the 15K resistor which should be soldered on the board. Actually I should buy the same resistors as the ones sold with the PCB, which is Vishay RN55D in 15KOhms of course.
- The power supply here is 240v and changes must be made from the pictures supplied in the excellent guide provided by Jim which is for 110v.
- The supplier of my transformer, Toroidy, provided a transformer with one primary 240v coil and two 18v secondaries. So the safety film capacitor of 0.0033uF (Panasonic ECQ-U2A332ML) has to be in parallel with the 240v primary, while the thermistor (or Inrush Current Limiter) has to be in series with it. I followed the advice of Mark for this ICL and took the SL 15-60002. You must buy two of them as there is another one for the ground.
- I had a hard time finding the fuses, slow fuses do not seem to be common, I finally get the ref 5TT 1.25-R.
- I read there was problem with the keratherm for the Mosfets being too thin and someone did bought some ceramic pad. I followed this advice and bought those pad (Aavid 4180G). I still used the keratherm underneath these pads. Somme problem, these pads have a certain thickness. So the Mosfet legs could touch the PCB and I didn't like it. So I had to find a way to elevate the PCB, the spacer being now too short. Keep this in mind.
- I used connectors instead of soldering for parts which might fail, so the replacement would be easier.
- I bought the Jfet from a dealer recommended by the boss himself, Nelson, but now they are in stock in the DIY store. Someone described a way to recognize if they were genuine Toshiba, a certain style of inscription, mine answered to that nicely.

Advices :
-I checked every and each piece received, every connection and soldering I made. That is compulsory !
- Read the guides provided, PSU and F5, keep them at hand, that is also compulsory!
- I suggest to use a solder made of both tin & lead and not tin alone ! If so, you need to heat up 70 to 80°celsius more ! This means you can deteriorate components beside having the need of a more powerful iron....and you better not need de-soldering if you ****-up !
- Before soldering P1 & P2, set them to zero and remember if you turn it clockwise or anticlockwise, record it somewhere, that is a must to simplify setting later on.
- Before soldering P3, set it to medium position for the same reason.
- Power the amp for the first time with the test light bulb. If it is fine, disconnect it and place a normal power lead.
- Take it really very easy when tightening the brass PSBs spacers , I cocked up and broke one even though I was gentle with the beast. I tried drilling and threading back....no way.
- Think carefully twice at what you are doing, what will come next and how to do it.
- Setting bias was a furious reading and I started to really understand only when I made the measurements. Easy when you know, Yogi Berra should agree with me on that one .
This need a complete clear procedure by itself.

My settings procedure :
Put in place the bulb tester and switch the power, the bulb should light up and faint ! If not something might be wrong > switch off > don't set anything , search what could be wrong.
If it is good, disconnect the bulb tester to proceed, otherwise all readings are going to be nonsense.

What you are after is voltage reading/setting.
You are going to do that with P1 - P2 and P3 for each channel. And if you have followed my advice, it should be alright.
Per analogy consider these like electronic dimmers. You set them to zero meaning no light, further you'll turn them more light you'll get. Here is the same, you have set P1 & P2 to zero, means no current go through you'll further enable them to let through the correct amount of current.
Forget P3, you have already set it at mid point, don't try to be clever, leave it this way.

- You want to make sure your PSU deliver around 50v.
- You want to make sure there is no voltage at the output where you connect you speakers cables, this means no distortion.
- You want maximum voltage at R8 or R7 to get maximum power (tell me if I am wrong here).

You are going to measure one channel at a time.
- You place voltmeter 1 at the output > in the banana plugs in place of your speaker cables > looking for Zero Volt. Reading here are in mV.
- You place voltmeter 2 on the V+ and V- of the PSU > looking for 50v or about
- You place voltmeter 3 on the legs of either R8 or R7 > looking for maximum voltage possible, you would probably never go over 0.6v.

Switch on and read the three voltmeters, you should get something like 50V at the PSU and Zero for the other two.
Turn either P1 or P2 one turn. Which way ? That's where you should remember which way you used before you soldered it. If you did clockwise, do it counterclockwise. Any change on the voltmeters ? Probably not yet.
Then turn the other one turn.
Carry on until you notice some changes. Now it's getting interesting. On mine, P1 set the Output and P2 the rail voltage.
Turn P2 to raise the rail voltage, then the Output should move one way, set it back to zero with P1.
Carry on until P2 has no more any effect, make sure the Output is zero with P1.
The PSU value should lower to 40 something.

Repeat the procedure to the other channel.

Once done, let it cook few hours and check every thing again.

Beside a ****-up (broke one PSB support) and one mistake (wrong wiring color), one cap leaking which has been changed, the amp worked straight out, flawlessly.
After a good three hours warming up, I started listening a CD I just bought and never it heard before. It was very pleasing.
Then I put some others I know by heart.
The first impression , it seems you had a big thick blanket covering your speakers and it has been taken away !
There is more of everything, a singer, an instrument, while being at the usual place, is more detached from the rest, more crisp, more micro dynamic, you get a true coherence from high to low.
I am listening often at night when everything is quiet and it need to be at very very low levels and often you lose a lot of details, the bass are gone etc...the F5 gives you all this back.

240 PSU.jpg - Google Drive
F5 board - Solder in process.jpg - Google Drive
****-up-copie.jpg - Google Drive
Rehausse-copie.jpg - Google Drive
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Wonderful!! Congratulations on your success!
:) :) :)

Now the very best part is hearing all your music as new again!

This amp would not be without your help, like many before me, I have no word to thank you enough.
I am not an "Hi-fiste" nor an electronic enthusiast as you know, I am a music lover....this F5 is running hard now.

This thread is my small contribution to give back the help I recieved with my words and my poor understanding of electronic things.

though - every silly pic repository , besides direct upload of properly shrinked pics to forum itself , gone and will go Dodo

Yes Zen, I know that but I never figure out how posting pictures directly into the post.
-insert link doesn't do it
-insert image does the same, it ask for an Http link !!! :confused: for me that one was supposed to do the trick.
So just now I notice "attachment" ...Lets try .


  • Completed-copie.jpg
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Congrats! I’ll soon be tackling my first amp build too, and there’s lots of good info here - thanks!! Do you recall the chassis and depth option you purchased? Would you recommend it to someone else tackling an F5?

It is the deluxe 4. If you notice I place the transfo flat you can gain space if you have a braket to place it vertical.
This chassis fit perfectly , don't forget you need space to work. Moreover every hole is made ready.⅝
Need to finish my Sissy SIT and am short of funds for the moment. I have some Kemet 47.000uf, 63v, PEH200MO5470MU2 caps and some 50uF Ducati caps. The big kemets are a challenge space vise for double mono in same kabinett (8 large Kemets take up a lot of space). I have used them in my M2 and the sound is good.
I dont have any powersupply sim software, would it be worth while to use either the Kemets as C, Kemets[C] and Ducati[c] as Cc or even CRc?

@Tooppy great F5 buld, sorry for sabotaging your thread.
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