Hey Pedro,
Sorry for taking so long to respond I've been on Holiday.
Don't worry about the sticker on my trano can, I stuck it on the wrong way round,
but the OEP can only go the RIGHT way onto the board, so don't panic.
You are right there is no R4/R9, because I'm using the trimmer. It is either
or, not both, that is prob why you are smoking stuff.
The idea was that R4/R9 47K was wired as a 'modest' guess for Biasing the
FETBoy but it is not very actuate hence the use of the 100K trimmer (BIAS / BIAS2).
There is an * next to R4/R9 which indicated to me that it might be optional
and looking at the original Hamptone design I saw this.
So remove the R4/R9, just have the trimmer in place and you should be fine.
Just check that nothing else smoked, but you should be up and running in no
time.
Also Q1/Q5 are the Jfets for the pre, it is not indicated in the BOM, but
you NEED these in order to have the pre work. The part I used from memory
was 2N5457 (I'll confirm this later).
But if you look at mine you will see I socked them, because you need to find
the best pair to work well together, as outlined in my set-up procedure in a
previous thread, which I'll post below:
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FETboy Fet Biasing procedure
1. Power up the pre without the fets (Q1/Q5)
2. Measure the V across R5
3. Adjust bias to have 4V across it (the trimmer)
4. Now put a fet in (Q1), don't solder it (I used sockets for my FET's)
5. Measure the V at the node before C2
6. Try all the fets you have and use the one that give you the nearest 12V
(Most of mine were around 14-15V)
7. If you get 12.3 or 11.7 just adjust bias to have 12V
8. Do the same for Q5 checking the V across R10 and the Node of C4
The other thing to do is to work out your HFE for the your Q2+Q3 and Q6+Q7 pairs.
The original uses a Darlington pair with an HFE of around 20,000! Fabio mimics
this with the BC550C's (I used BD139-16's). Try and match your HFE of those pairs
to give you close to, or over 20,000 HFE. Q2xQ3 = +- 20,000 HFE, and the same
for the other pair.
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I hope that helps you. Let me know ifyou need any more help.
Cheers
Matt
