BSIAB2 Weirdness

[jimmy54]

Hi folks,

Just finished a BSIAB2 build and something is strange is going on.  The BSIAB2 seems to work (i.e. the sound is good, very good actually).  But when the guitar volume pot is low (with humbuckers) or single coils are used, the sound is splatty and ends abruptly.  Also if a note is held for a while, then as the volume drops off the sound goes splatty  (i.e. it appears to go splatty if the input to the pedal is low).

I've checked the transistor voltages and they are as follows:

Q1   G  O
   S  0.66
   D  4.85

Q2   G  4.O
   S  4.8
   D  8.4

Q3   G  O
   S  0.09
   D  4.3

Q4   G  4.0
   S  4.3
   D  8.4

Q5   G  -0.7
   S  0.73
   D  0.80

Q1, Q2 and Q4 seem to pretty much to match the voltage diagram on JD's GGG site but Q3 has wrong voltages (G is 0v instead of 0.3v and S is 0.09v instead of 0.75v)) and Q5 has wrong voltages (G is minus 0.7v instead of 0.5v, D is 0.8v instead of 3.4v).

I used a 250pf cap (instead of a 150pf cap as I didn't have a 150).  Could this be responsible for the wrong voltages on Q3 and Q5?

Any advice appreciated.

Jimmy

[bluesdevil]

Did you adjust the trimpot? That can make a difference in note decay.

[jimmy54]

I did but it didn't seemed to help any.  It did change the noise (hiss) of the pedal though.

[bluesdevil]

If adjusting the trimpot isn't helping, I would definitely trace back from the pins that are getting the unusually low voltage readings..... reflow the solder around them and the parts leading to 'em. If that doesn't get you any better results check for solder bridges either using your DMM's continuity tester or scrape a utility razor blade between traces very carefully. Good luck!!