intermittent bass farts from BSIAB2

[euronymous0001]

i wanted to make my BSIAB2 to have a sound similar to a boosted marshall, so I made an LPB and really liked it.

however, when I incorporated it inside the box, it made intermittent bass boosts (like your cranking a bass knob)

the BSIAB2 is modified with Jack Orman's Presence control and the rest is stock (gaussmarkov version).

the LPB, looking at  this http://www.beavisaudio.com/techpages/SchematicToReality/, has R2 and R4 with
470k and 47k respectively (also tried 430k and 43k) and C1 and C2 changed to 2n2 and 47n. and lastly removed VOL pot
and put a 100k resistor to ground to mimic a vol pot set to max vol.

TIA! 

[euronymous0001]

put 100R resistor from 9V to the board did not resolve the issue. i'll be removing the LPB tonight and see if it cures the problem 

[euronymous0001]

removed the modified LPB and its all normanl now. i think i need to rebuild another modified LPB and see if the earlier one was the culprit