GGG BSIABII

outoftune · July 02, 2007, 10:23:19 PM

So I finally got building some stompboxes. I ordered this pcb among others from ggg. I know how to solder and all that. (my first build was actually a byoc sg which i just revisted and got working). I just finished my sophomore year as a ee major, so I know the basics about circuits. Now that I got that background out of the way here is the issue.

The BSIABII works, but I do not think it is working correctly. I adjusted the trimpot as told to do here: http://generalguitargadgets.com/pdf/ggg_bsiab2_instruct.pdf
All the transistor voltages look about right EXCEPT Q3. The drain voltage is about write but the gate voltage is very close to zero and source voltage is only about 30mV.

Now for what I hear. Holding out a chord I hear quite a bit of oscillation. Also I heard this pedal can do low distortion alright, but I was not able to get any sort of low distortion out. When I had the gain turned down lower, I couldnt get the volume up enough to balance out. If there are any other voltages I should measure I can. Oh here is a link to the schematic and layout respectively: http://generalguitargadgets.com/pdf/ggg_bsiab2_sc.pdf http://generalguitargadgets.com/pdf/ggg_bsiab2_lo.pdf

Pushtone · July 03, 2007, 12:58:40 AM

Compare your voltages to this post. They should be close-ish
http://www.diystompboxes.com/smfforum/index.php?topic=52409.0

Keyword search: "BSIAB voltages"
There are several debugging posts besides the above.

Good Luck

96ecss · July 03, 2007, 01:08:36 AM

If you follow the instructions here http://www.diystompboxes.com/smfforum/index.php?topic=29816.0, someone will be able to help you sort it out.

Dave

Edited for spelling.

outoftune · July 03, 2007, 12:20:07 PM

I'll have to retake measurements of all the transitors again sometime tonight. Like I said though Q3 was the only one that had some stuff that wasn't really close at all. There's only one thing I used that was not exactly called for and I'm not sure the difference. I used J201-E3 rather than just J201. Apart from them both being NPN I don't know anything about them, or if they are different in any significant way. I looked at the datasheet but was not able to find anything about the E3. I read some of the other threads regarding the BSIAB and found that I may like the 2N5457 better everywhere... but I think there is something else other than just preference that is off. Like I said, I'll post all the transistor voltages tonight. Thanks for your help.

Barcode80 · July 03, 2007, 02:18:38 PM

if you used a J201 there is a good chance that if you try 3 or 4 other j201's in its spot it will work. the J201 is an inconsistently manufactured device and if you get a screwy one you'll never get a good bias.

outoftune · July 03, 2007, 04:51:54 PM

well Q3 is a j201 and it is the one that had some funny readings, so I'll try replacing that tonight.

outoftune · July 04, 2007, 01:00:11 PM

Well I changed out Q3 for a 2N4547. Then I took all the transistor voltages. Something's definitely up.

Q1:    G: 0
   S: 0.602
   D: 5.36

Q2:    G: 8.72
   S: 5.36
   D: 4.13

Q3:    G: 0
   S: 1.22
   D: 3.388

Q4:    G: 4.17
   S: 4.13
   D: 8.72

Q5:    G: 0
   S: 1.22
   D: 3.390
Any helpl would be greatly appreciated. Thanks.

Ed G. · July 04, 2007, 01:19:28 PM

Since the source of Q4 is connected to the drain of Q3, those voltages should be EXACTLY the same. Look at the drain of Q1 and the source of Q2. That is how it is supposed to be. Unless you are not taking the voltages correctly, something is wired wrong or there is a solder bridge somewhere.

outoftune · July 04, 2007, 04:45:15 PM

I found a mistake. I accidentally hooked up a wire to the ring of the input rather than the sleeve... Now my voltages across Q3 read Q3:
   G: 0
   S: .150
   D: 4.13

That's still a bit off although it corrected what you pointed out Ed. One other thing I did was rather than having two wires go to the ground of the dc jack and the sleeve, I had one go the the dc jack and one go from there to the sleeve of the input. But it's all one node so that shouldnt matter... right? Any other things I should look for? Thanks a lot for your help so far.

outoftune · July 05, 2007, 09:03:17 AM

anyone?

outoftune · July 06, 2007, 12:58:13 PM

i know someone can help with this, as you already have. more input would be appreciated. thanks.

oskar · July 06, 2007, 01:30:53 PM

Quote from: outoftune on July 06, 2007, 12:58:13 PM
i know someone can help with this, as you already have. more input would be appreciated. thanks.

One of Q3/Q4 isn't soldered properly, where they are connected they should absolutely have the same voltage.
Battery unconnected, meassure resistance Q3 drain/Q4 source. Meassure both the trace, and from componentlegs.

Ed G. · July 06, 2007, 03:45:35 PM

Quote from: outoftune on July 04, 2007, 04:45:15 PM
I found a mistake. I accidentally hooked up a wire to the ring of the input rather than the sleeve... Now my voltages across Q3 read Q3:
   G: 0
   S: .150
   D: 4.13

That's still a bit off although it corrected what you pointed out Ed. One other thing I did was rather than having two wires go to the ground of the dc jack and the sleeve, I had one go the the dc jack and one go from there to the sleeve of the input. But it's all one node so that shouldnt matter... right? Any other things I should look for? Thanks a lot for your help so far.

Well, what you did might have fixed another problem, but it did nothing for the problem you have, which seems to be that the source of Q4 isn't connected to the drain of Q3. Look at the schematic. Maybe you damaged a trace, or didn't solder the fet in well enough to make contact. At the risk of repeating what Oskar said, take out the battery and test the continuity of the circuit between Q3 drain and Q4 source. You have a continuity function on your meter, I hope. Or just read the resistance. Like he said, measure from the component legs. If the meter doesn't beep, then the circuit is not making full contact somewhere.

outoftune · July 06, 2007, 04:44:12 PM

Quote from: Ed G. on July 06, 2007, 03:45:35 PM
Quote from: outoftune on July 04, 2007, 04:45:15 PM
I found a mistake. I accidentally hooked up a wire to the ring of the input rather than the sleeve... Now my voltages across Q3 read Q3:
   G: 0
   S: .150
   D: 4.13

That's still a bit off although it corrected what you pointed out Ed. One other thing I did was rather than having two wires go to the ground of the dc jack and the sleeve, I had one go the the dc jack and one go from there to the sleeve of the input. But it's all one node so that shouldnt matter... right? Any other things I should look for? Thanks a lot for your help so far.

Well, what you did might have fixed another problem, but it did nothing for the problem you have, which seems to be that the source of Q4 isn't connected to the drain of Q3. Look at the schematic. Maybe you damaged a trace, or didn't solder the fet in well enough to make contact. At the risk of repeating what Oskar said, take out the battery and test the continuity of the circuit between Q3 drain and Q4 source. You have a continuity function on your meter, I hope. Or just read the resistance. Like he said, measure from the component legs. If the meter doesn't beep, then the circuit is not making full contact somewhere.

Ok. Maybe I'm totally missing something. I also thought that what I did would have no effect on the problem you pointed out. But if you look at the most recent measurements of Q3:

   G: 0
   S: .150
   D: 4.13

The drain does match that of the source of Q4:

G: 4.17
S: 4.13
D: 8.72

Thanks again for the help.

oskar · July 06, 2007, 05:17:34 PM

Oops!
I didn't read through properly, have a hard time with long texts you see.

The way I see it there is two places that looks interesting. Q2/C2, Q4/C7.
If the Drive pot also has an effect on the ringing then the problem obviously is after it = Q4/C7
Otherwise it is around Q2/C2 you should focus.

oops! gotta go!

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