Mach 1 background hiss

[falco_femoralis]

Hi all, I built a Mach 1 a while back, really great low gain overdrive, perfect for sparkly cleans. It's worked great but today I noticed if I sustain a note with the pedal on, there is a slight background hiss noise that becomes apparent when the note begins to decay. It's subtle but it's there, like a noise gate being held open while the note is sustaining and then closing when the held note passes below a certain amplitude. None of my other pedals do this. It's affected by the gain control - turning clockwise increases the hiss.

The hiss has the quality of an overdriving transistor - it's somewhat spitty.

Here's the inside of my pedal. I've tried moving the wires around isolating them from the caps and there's no change in sound. Where should I start?

 

[Nostradoomus]

this has been an issue with fake op amps, what did you use and where did you get it?

 

[Markus Kersius]

I got a similar issue with a Shrapnel (thorpy gunshot) I've build.
When a note sustained and decayed slowly a sort of silent crackling appeared a then the note just stopped like it's beeing cut off suddenly.
I was a bad (fake) opa2134.
Swapped a tl072 in it's place.. problem gone.
I can't remember where I got the opa2134 from.

 

[falco_femoralis]

^ that's good info. I would have gotten the op amp from Tayda or Small Bear. It's the spec opa2134. I'll take it out and try swapping and see how it goes. Thank you.

 

[swelchy]

Another good practice is to use as little off board wiring as possible... Dont have signal wiring from your switch board crossing over components on your pcb and also sand/scrape contact areas for jacks/switches on your enclosure to bright metal... I even go as far as cleaning the paint from one screw hole in backplate so the screw head completes the ground for the back cover...