Boss FA-1 build report and a strange problem with it

[gigimarga]

Hello,

A couple of days ago i found in my "almost-ready-to-go-to-the-trash" box a clone of a Boss FA-1 (using this project: http://ustomp.com/?p=6).

After retesting it (i forgot why i didn't like it...), i saw that it works OK, but it has a very strong noise.
After rechecking the schematic (http://ustomp.com/files/fa1schematic.pdf) i saw that the PCB didn't have both 100pF capacitors from the schematic (C13 and C14). After i add C13 all the noise was gone and it worked very well.
I forgot to say that I used 2N5457 for the FET and NE5532 for the IC and i've added a 2.2M pull-down resistor at the output.

When i start to test it i saw that it has a big problem: the treble pot makes a strong popping at 2/3 of its value (it was a 47K liniear pot)!
I replaced it with a new 47K log pot (i found that in a Baxandall circuit the pots are log) and, very strange, the same problem!!!

So, why i have this strong popping from the treble pot??? I need a 50K pot instead of 47K?

Thx a lot all!!

[gigimarga]

 

[blueherdim7]

Hi-

I have built several of these and they all were great.  A couple self induced problems, but nothing major.  I used the layout from ustomp...did you use a non-polar 47uF cap for C2?  There was a discussion on another thread that mentioned the difference in the schem vs. the layout...  .47uF in the schem and 47uF in the layout.  I tried an a/b and the .47uF gave alot of noise....the 47 sounds great.

Jon

[gigimarga]

Thx a bluehermedim7...I used a 0.47uF NP...it seems to me (and not only to me...) that 47uF it's too big!

[blueherdim7]

I wish I knew more about it to say...I thought the same thing, but, it made all the difference when I swapped it.

Jon

[gigimarga]

Anyway, a 47uF NP i don't have...a 47uF electolytic it's ok?

[gigimarga]

Last night i added the second 100pF cap, i replaced the 47K log pots with 50K log pots and it sounds very well!
After all, I replaced the 0.47uF with a 47uF electrolytic, but i didn't heard any difference.

Thx a lot all!