Intermittent problem with Peppermill build

[PCR]

I have built the Peppermill overdrive circuit at the Runoff Groove site and am experiencing some perplexing intermittent problems.  Here is the circuit:

http://www.runoffgroove.com/peppermill.html

When I turn the circuit on it will work properly for a few minutes and then:
1.) stop working all together- like it is completely grounded out
or
2.) begin to go lower in volume and start emitting a static like noise
or
3.) the gain control will stop working

I have tried to trouble shoot this with a sound probe and can trace sound all the way to lug 2 of the gain pot.  The first stage through the BS170 works and then there is no sound at either the D, the G, or the S on the J201. For all three of the intermittent symptoms that I am experiencing the sound has been present through the BS170 first stage, so I am thinking that my problem is in the second stage somewhere.  Every time that I have used the sound probe to trace the failure, at some point in my probing I have touched different points in the second stage circuitry, and will hear a pop, and then the unit is fully functional again only to have one of the 3 failure types above reoccur a short time later.   I have replaced the J201, have replaced the 1 uf electrolytic cap, and have replaced/resoldered the leads going from lugs 1 and 2 on the gain pot to the board, but the problems persist.  I have examined the solder points and everything looks okay.  I built this on a Radio Shack perf board like pcb.  Voltage at drain on the J201 is 4.5v. Any help will be much appreciated!!

[LucifersTrip]

is the problem the same with a DC adapter and battery?

[PCR]

I have it set up to run on battery power only.

[PCR]

I think (hope) I have figured it out.  I went over my solder joints with a continuity tester and found a bad connection (even though it looked fine) between the J201 S pin and its connected components .  It seems to be working fine now.