My circuits work properly for a minute then THE NOISE starts - please help!

[claviolog]

Hi! I'm a novice to electronics. I've built 3 circuits so far - 1 works perfectly (it is a copy of my Eurotec Black Box Fuzz module with the addition of an intensity pot), the other two have the same problem. The 2 not working properly are a Zonk Machine circuit (from an online circuit) and a copy of my dads 1973 Colorsound Overdriver - the problem is the same with both: they work for around a minute and sound like they should, but then there's a pop, a few seconds gap, a crackle and a pop, followed by more pops, crackles, sound drop-outs and drop-ins all getting more and more frequent and more and more intense until the guitar signal and correct sound of the pedal has completely gone and all that is left is intense popping and crackling. I don't understand what is going on or what I've done wrong. The Overdriver circuit is identical to my dads (it's the version with 100k treble and bass pots and a 2k2 drive pot with three BC169B transistors) - it was a straight copy. The Zonk has only one mod - I am using three NOS Mullard OC71 transistors not two OC44 and one OC75 like the original (OC71's sound better in other pedals I've owned and tried than other versions with more common transistors). The transistors were tested before being put in the circuit and all were good. I'm particularly confused because my 1st pedal (the Eurotec fuzz clone) works perfectly even though it was alot messier (it was my first attempt!) Any ideas what I've done wrong?

[amptramp]

Have you checked the polarity of any electrolytics you have used?  If they are in backwards, this would give the same symptoms you are describing.

[LucifersTrip]

check to see if the same thing happens with a different power supply