BSIAB2 debugging problem

[Just1More]

Hi

Just about finished my first build, but have some problems with the sound.  Just wondering if anyone can point me in the right direction re: debugging.  Here's the background

Project: BSIAB2 from General Guitar Gadgets
Source web site: http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=105&Itemid=26
Schematic: http://www.generalguitargadgets.com/pdf/ggg_bsiab2_sc.pdf
Layout: http://www.generalguitargadgets.com/pdf/ggg_bsiab2_lo.pdf
Reference voltages: http://www.generalguitargadgets.com/pdf/ggg_bsiab2_instruct.pdf

The project was built from a kit with no part substitutions.  One of the supplied resistors was the wrong value but that was replaced before assembly.  I have double-checked and triple-checked the orientation of the JFETs, diodes and electrolytic caps and all looks good.

Sound: Bypass signal is working perfectly.
Switched it on.  LED comes on bright and strong [anticipation building].  Increased the volume to about 9:00 on the pedal and strummed a power chord.  Got a spluttery, fizzy, farty sound that only really comes through when you play hard.  There is no sound at low volumes.  You have to really dig in to get anything.  I guess this was part way successful give a first build.  Sounds very similar to this thread, but unfortunately there is no information about the resolution: http://www.diystompboxes.com/smfforum/index.php?topic=57445.0

Checks revealed the drain voltage at Q5 was way below the reference level of 3.4V.  Adjusted to 3.4 and tried again.  There was a glorious, Marshallesque, brown sound for about 20 seconds and then it started spluttering again.  Haven't got any further from there.  I have tried various settings in the 3V to 4V range but it doesn't seem to make much difference.

Voltages:

Battery: 8.98V
Battery with circuit load: 8.96V
Battery lead on board: 8.88V

Q1 Actual (Reference)
G: 0v (0v)
S: 0.35v (0.95v)
D: 4.95v (4.5v)

Q2 Actual (Reference)
G: 4.24 (3.8V)
S: 4.94 (4.5)
D: 8.89 (8.0)

Q3 Actual (Reference)
G: 0 (0.3)
S: 0.06 (0.75)
D: 4.5 (4.3)

Q4 Actual (Reference)
G: 4.21 (3.8V)
S: 4.25 (4.3)
D: 8.85 (8.0)

Q5 Actual (Reference)
G: 0 (0.5)
S: 1.44 (0.9)
D: 3.39 (3.4)

Any suggestions for where to start looking.  Could there be an issues with the closeness of gate and source at Q4?  I will test it out with an audio probe, but probably won't get a chance until the weekend.

Any suggestions greatly appreciated.

Thanks

[Krinor]

To me this sounds like either a bias problem or a capacitor missplacement. I'm not the most experienced around here, but I'd suggest replacing the jfet for another one. You can switch places using the ones you already have. You DID put in sockets didn't you ? Always smart with jfet builds. (I wish JD would supply sockets and replacement jfets with this kit). Check all your cables thoroughly (90% of the problems I've had with any build has been a loose joint - usually on the jacks or on the switch). Check for soldering bridges. Maybe not likely since you probably did a neat job, but even the smallest shorting will cause trouble. This effect sounds great. Just give it some more time and you WILL eventually find the bug 

[rockford]

Something similar just happened to me, I changed out a cap, and found out later I used too much heat in doing so. I fried one of the transistors,
Bypass was fine but when switched on, there was almost no sound.

[DougH]

Q3-S looks low. The other voltages look okay. Reflow all your solder joints and re-check your wiring.

[Just1More]

Thanks for the input.  Stoopid-head here hadn't soldered one of the connections between the drive and volume pots  .  All sorted now.

This thing sounds awesome!!  Nice fat distortion - far superior IMO to the Boss DS-1 (which is the only thing I really have to compare with).  Should complement my Fulldrive 2 nicely.  Tone control seems to have a very wide frequency range and can really change the sound.  It cleans up pretty well when I roll back the volume control on my strat.

Thanks again.