fatpants issue

[sam_c]

(1- name) Fabbed Fatpants V2
(2-problem) On my second fatpants build now and the circuit is working fine with the 'fat' pot fully open, but when its not at its max setting I get a very sudden drop in gain and output then the pot acts normal reducing the overall gain to zero through its rotation.
(3-fix attamepts) tried a new gain pot, but got the same fault.  Gonna try a new J201 later today incase I damaged it.
(4-subs) no subs, all stock parts as per BOM.

When i get back in later today I will take some pics and take some voltages at the IC and transistor.

thanks in advance!

[madbean]

So, the drop out only happens when you start changing the pot setting, but after a second or two it comes back? If that's the case, then it's normal. Or, have I misunderstood what you wrote?

[sam_c]

No, when I start to turn the fat pot down from its full position, the output drops suddenly and doesnt recover.

[madbean]

No, when I start to turn the fat pot down from its full position, the output drops suddenly and doesnt recover.

Right, what I'm asking is: when you turn the Fat Control down a bit, the output drops out for a second, you maybe hear a slight scratchy sound and the overall gain/volume is reduced when it comes back. Correct? Or, by "it doesn't recover" you mean unless it's at its maximum there is no gain at all through its rotation. Sorry, just trying to be precise so I know what is going on.

[sam_c]

by "it doesn't recover" you mean unless it's at its maximum there is no gain at all through its rotation. Sorry, just trying to be precise so I know what is going on.

no problem,  I'm having a hard time describing it.

Your are correct, fat pot at maximum the pedal works as it should.

When I start to turn the pot down, the output drops to say a quarter of what it should be.  It doesn't dip out and come back.

another way to describe it, I'm getting maybe 0-20% output through nearly the full rotation of the pot, but only getting 100% output when the pot is fully rotated.

Ive built a working fatpants and egodriver before this one, just having an issue with this other fatpants.

[sam_c]

some more info.

IC voltages...

1  -  9.03v
2  -  4.4v
3  -  0v
4  -  0.17v
5  -  0.37v
6  -  4.54v
7  -  7.02v
8  -  9.04v

JFET (trimmer all the way down)

d  -  7.28v
s  -  0.08v
g  -  0v

JFET (trimmer all the way up)

d  -  16v
s  -  0.08v
g  -  0v

[jkokura]

What I would do is double check that C3 and R3 are the correct values and are soldered in correctly. It sounds to me like something isn't grounding properly around your pot and transistor.

Jacob

[sam_c]

Thanks Jacob,  I will check those out later today.

[sam_c]

man, do I feel like a dumbass.

I checked over all the parts and reflowed all the lugs and had the same issue.

I decided to check the resistance across the fat pot to rule that out again and got ~100k....

Id got the vol and fat pots mixed up 

sorry for not noticing earlier and thanks for trying to help me out, it is much appreciated.

Pedal sounds great now! which is good as my bandmate has claimed the first fatpants I built for himself