BSIAB troubles. No sound, where to probe?

[remmelt]

My BSIAB2 (ggg) does not produce sound. Bummer!

Here's a breakdown of GGG's voltages against mine:
GGG:9v, D of q5 trimmed to 3.4V
Me: 9.06V, Drain Q5 @ 4.03V

Q	Transistor Leg	GGG value	My Value
Q1	Drain	4.5	4.60
Q1	Source	0.95	0.710
Q1	Gate	0	0.001
Q2	Drain	8.0	8.45
Q2	Source	4.5	4.60
Q2	Gate	3.8	4.02
Q3	Drain	4.3	5.00 or 4.26
Q3	Source	0.75	0.001
Q3	Gate	0.3	0.005
Q4	Drain	8.0	8.42
Q4	Source	4,3	5.00 or 4.26
Q4	Gate	3.8	4.01
Q5	Drain	3.4	4.01
Q5	Source	0.9	0.741
Q5	Gate	0.5	0.001

I'm getting inconsistent readings... It's pretty weird. One moment Q3's drain says 5, the other it's 4.26. I can't seem to find a pattern. Sometimes it's even as low as 3.97. Most of the readings are ball park, I've marked the three that are off.

I'm trying my hand with the audio probe, but I don't know what to listen for. Which leg should sound like what? I understand that +9V and ground don't sound like much at all, but what should the rest of the path sound like?

Junction of Q1's D and Q2's S: pretty loud, somewhat distorted sound. Lots of high end. No effect from any of the knobs, obviously. I guess this is how the first stage should sound.

Junction of Q3's D and Q4's S: very loud, sound only comes through when playing hard, it's very gated and it sounds terrible. No effect from the Drive knob. I can get a pretty convincing electro-fart sound from touching the drive's wiper with my finger. Sometimes there's extreme squealing.

Q5's G: no output, which means no input for this stage. That's wrong, I presume.

How can it be that the junction of Q3+4 produces sound (although nothing to be proud of) but Q5's gate sees nothing? It's connected through C12 and R14 only...

I've used the PCB from GGG, all new and marked caps and metal film resistors. It's not boxed; it's on my desk with short solder-tacked on leads. The leads are 5cm (2") max. It looks tidy enough. All grounds are alligator clipped to a single point, continuity check for ground points is OK.


Anyone have any idea what I should be looking at? Should I try exchanging the FETs?

The effect as it is draws 1.19 mA of current.

[remmelt]

I'm bumping this... anyone have any idea what could have gone wrong in my build?

[GREEN FUZ]

I'm trying my hand with the audio probe, but I don't know what to listen for. Which leg should sound like what? I understand that +9V and ground don't sound like much at all, but what should the rest of the path sound like?

Doesn`t it just make a sound when there are no breaks in the circuit?

[aron]

>I'm trying my hand with the audio probe, but I don't know what to listen for. Which leg should sound like what? I understand that +9V and ground don't sound like much at all, but what should the rest of the path sound like?

Test right at the input to the board. You should hear your guitar.

After that, listen at every gate pin of any "bottom" FET, when you don't hear anything, the problem is in between that point and the last point that you heard sound.

Aron

[petemoore]

 See 'mini booster' or Mu Amp [Amz / Geo].
  This is about what's in a gain stage of the BSIAB.
  The input to the first stage should sound like the tip of the guitar cable plugged into the input jack, if no sound there, test that ground hasn't strayed to the input.
  The output of each mu stage should be sinfignacently louder/distorted than it's input [first stage lightly distorted booster output like minibooster, second stage [if seeing first stage signal at input..] should also further boost/distort quite a bit.
  Inside each stages output decoupling cap you should find about 1/2v biased on the 'Q1'd/"q2'S' connection...the top Jfet biases the bottom Jfet, look for vbias of 1/2v at voltage divider also.