Big muff triangle sustain problem

[Trouffion68]

HI guys

I have bredboard my first big muff  the triangle version. I found the big muff sound signature but with less sustain.
I have isolated the gain section and I think the problem is here.

With only the gain section ( just after the sustain pot) I have no sound when the sustain pot is off. IT start to have sound on 10%. No boost until 50%

The final result is a big muff only if we put sustain and volume pot on max.

Have you any idea?

Thank's for your help.

Nicolas.

[GibsonGM]

What value and type of pot did you use - not an "A" taper, right?  Look on the back for the resistance and a letter, usually "A" or "B".  Is there a resistor to ground from the sustain pot?   BMP schematic shows a 1k there.  Can you post the schematic YOU used?

Welcome to the forum, by the way  

[Trouffion68]

Thanks for your reply. Great community.

I have try both log and linear  (100K) try many shematics version. Always thé samedi problem.
Yes a 1K resistor is wired on the first lug of the pot. ( I have verify this resistor many times because it's her that let pass a minimum of input signal when the pot is totally OFF.

UPDATE : I can hear un little signal (not good quality) when the pot is OFF if a crank the amp volume, so somethink pass...

There is the schematic I have used :
http://www.bigmuffpage.com/images/schematics/V1%20SCHEMATIC%20Perf%20Board%2066_no_5.jpg

Thank's for your help.

Nicolas.

[GibsonGM]

There are a few ways to look at this, Nicolas.  You can check each component in the gain stage just after the sustain pot.....post voltages for C,B, E.   Could the input cap be bad?  Odd symptom if it is 'pot related'...  Re-check to be sure each part is there and not shorting.  Also check the output components of the stage before the pot (the output cap etc).

You can audio probe that section, to see where the trouble lies.

If neither of those work, you will have to fill out the 'debugging' info and post back here.   The debugging questions are here:  http://www.diystompboxes.com/smfforum/index.php?topic=29816.0


I would like to know the transistor voltages for the stage after sustain pot when it is NOT working, and when it IS!

[Trouffion68]

So I Have prob The gain stage and it's definitly The source of problem.

I Have rebuilt it on breadboard with new parts and nos it's OK.

Thank's for your help. The good thing about Having problem on a build is that After we handle the schematic.

[GibsonGM]

   The good thing about the problem is that you learn something...bread boards can be a little unreliable!   

I am happy for you, enjoy the muff!