Help with Mxr Gt-Od

[niko12345678]

Hi Guys,
I'm building this pedal for a friend but i cant get it to work right, i'm using this layout with a RC4558P. http://3.bp.blogspot.com/-VCScwlgYjl4/UQU9D5JhTtI/AAAAAAAAEfU/h4x9E02pZYU/s1600/MXR+GT-OD.png

When the gain is at 0 the pedal works fine the problems come when i try to increase the gain.

When the OD/ZW switch is engaged increasing the gain causes the pedal to oscillate (a very loud WOOOOOOB)
when the OD/ZW switch is disengaged the gain has no effect at all

I tried to check for shorts or wrong components but i haven't found anything.
I tried to use a fixed resistor instead of the Gain pot and to put the circuit in a metal box to isolate it but still nothing.
Tried different transistors and ics, still nothing.

I still haven't tried to use a battery instead of the boss dc source, but i'll try tonight.

Here is some pic of the thing: http://imgur.com/a/AHlDc

 Do you have any idea on what i should check next?

[IvIark]

Maybe a faulty Gain pot?  But looking at your solder side picture there looks like there are quite a few places where unwanted bridges may have been created.  

Cuts look ok to me but it's still worth going over the cuts again after soldering, just in case any burrs are left in there or any solder is causing a short:


But some of those stray strands could definitely be causing an issue:

[niko12345678]

Thank you for your time,
I tried to use a fixed resistor instead of the pot with the same results so i think the pot its ok.

After the build i checked for shorts with a multimeter and everything seemed ok, but yes the points that you highlighted look bad indeed.

Tonight i'll try to trim those a little bit, i'm pretty sure they dont touch but maybe it can be some kind of parasitic capacitance or something (is that a thing?).

Thank you again,
i'll keep you posted