HELP WITH BSIAB2 FROM GGG

[Govmnt_Lacky]

I just finished the BSIAB2 from GGG. I etched the board myself. I have read all the info on this site and so far I have not found any problems like this so hear goes.

First of all it works in bypass. I used the transistors recommended on GGG (J201 & 2N5457). The problem I am having is that when the effect is on, I have to strum VERY HARD to get any sound from it. It is distorted like it should be however, as the notes/chords ring out and go into sustain it get fuzzy and/or scratchy and disappears! I really have to keep strumming HARD to keep the sound coming through. If I finger pick a note or just strum lightly there is NO sound. I read out the tranny values with a wall wart (14.1VDC) and they seem comperable to what JD lists on his build instructions (he used 9VDC regulated and mine is 14.1 wall wart) So where he has 8VDC, I have about 12.4VDC and so on. Dont have the readings handy right now but I can list them later. I am wondering if I would need to match the J201s and 2N5457s or even replace the 2N5457s and put in all J201s or vice versa. Any help would be greatly appreciated.

[DWBH]

Have you tried fooling with that nasty trim-pot?
What voltage rating are your electro caps?

[Govmnt_Lacky]

Turned the trimpot from one end to the other with no change.
The only electrolytic cap in the circuit is a 100uf and the one I used is rated at 16V.

Hope that helps.

[Govmnt_Lacky]

Looking at the circuit, I do have one thing to add. I did not have a 250pf cap for C1 so I used a 270pf cap instead. I did not think this would have any real effect on the circuit however, you are all the experts. I am just a guy here with a half-broken effect.

[slacker]

I don't think the extra voltage will cause any problems but just in case try it with a battery.  Other than that I'd make an audio probe and poke about to see where the problem is. Try listening to the signal at the wiper of the drive pot, you should get a loud boost. If that's Ok listen to the sound where C12 and R14 join, you should get a loud distorted sound. If that's Ok then the problem must be after Q5.
Once you've found where the problem is start checking for the usual things, solder bridges, cold joints incorrect component values etc.

[Govmnt_Lacky]

Slacker,

When you say to check at the point where C12 and R14 join, do you mean check the sound at Q5's gate? Dont have an audio probe (Yes, I know.... you dont have to say it) but I will look around to find out how to make one.
Do you think in the slightest that one or more of the transistors could be to blame? OR that they need to be matched for any reason?

Thanks for the advise. Any other suggestions would be welcome.

[slacker]

When you say to check at the point where C12 and R14 join, do you mean check the sound at Q5's gate?

Yeah, don't know why I didn't just say that 

You don't  actually need an audio probe to check the circuit. If you disconnect the output wire that goes from the board to the volume pot at the board end you can just use that. Plug your guitar into the input jack and your amp into the output jack, and turn your amp down low.
Then touch the wire you just disconnected to the wiper of the drive pot and the gate of Q5 whilst playing and see what you get.

[Govmnt_Lacky]

Slacker,

I will try your suggestions as well as post my tranny voltages in a few minutes. Please check back later (probably before 3:30 EST) and see my response. I really wanna get this working.

[Govmnt_Lacky]

Here is what happened:

I checked the signal at the Drive pot wiper. There was a SOLID clean audio boost. No apparent problem.

I checked the signal at Q5s Gate. The signal was EXACTLY like it is from the output jack. Distorted but, no sustain and as the sound fades it gets crackly and then nothing. Just like the original problem.

Here are the tranny voltages (14.1VDC wall wart)

Q1) Drain: 6.63  Source: 0.477  Gate: 0
Q2) Drain: 12.48  Source: 6.63  Gate: 5.92
Q3) Drain: 7.05  Source: 0  Gate: 0
Q4) Drain: 12.46  Source: 6.25  Gate: 5.94
Q5) Drain: 1.85  Source: 0.653  Gate: 0

[slacker]

Looks like something's wrong with Q3 and Q4. The source of Q3 should not  be 0 volts, check the connections of R10. The drain of Q3 should be the same as Q4's source because they are connected together so check round there.

If you've socketed the Fets try putting Q3 and Q4 in the Q1 and Q2 positions and then listen to the signal at the drive pot. That should show up any problem with the fets themselves.

[Govmnt_Lacky]

Unfortunately I wasnt smart enough to socket the FETs. I do understand what you are saying about Q3 and Q4. I did notice that I used a 130ohm resistor in R10 instead of 120ohm. Would that make a difference? A visual of the PCB does not reveal any obvious errors in the work. I am starting to think that either Q3 or Q4 is suspect. Most likely Q3. I will have to wait till tomorrow to do more debug but I will keep you informed. Thansk for all the help.

Any other suggestions would be appreciated!!!!!

[Govmnt_Lacky]

OK.... bring out the "Nice Job Moron!" I just noticed that I forgot to wire the groung from Leg 1 of the Volume pot to Leg 1 of the Drive pot. I am wiring it in right now and will have to test it tomorrow. Could this cause my issues?

[oskar]

Could this cause my issues?

Yes!