Help with BSIAB II

[erick4x4]

Ok so I just built my second BSIAB ii. Basically normal except put a 1M pot in for R6 for more mid control. and switched C2 and C7 between .1uf each or .2uf each for more high mid control.

I have really checked every part, solder joint, wiring, etc, and I need help!

I get extremely low output, with no distortion.  Gain and volume lower what little volume I have, the same amount. However, one positive note the tone control works, as does my 1M pot, and switch.

Here are my voltage readings: help! using a power supply ay 8.99v

Q1: G 0v
       S .2v
       D 5.6v
Q2: G 4.5v
       S 5.62v
       D 8.99v
Q3: G 0v
       S .033v
       D 4.76v
Q4: G 4.48v
       S 4.76v
       D 8.99v
Q5: G .002v
       S 1.03v
       D 1.40v

If I adjust the trim to try and change Q5, all other setting are no output.

It sure seems like Q3 and Q5 have issues, but what parts should I be checking/replacing to try and correct it?

Thanks for your help!

[erick4x4]

Sorry for the bump, I'm a touch desperate, really trying to finish this for a gig this Friday

[Traintrack]

I had my 2nd BSIAB build kick my butt during Easter. For me it was discovering a bad solder joint on a cap. I must have stared at the board for hours until I finally saw it. This is after desoldering many many parts that I thought might be defective!

I did a search for BSIAB here and read every thread I could find to see if anyone was having the same problems as I was. And there was on guy that did, and it was a bad solder joint on a cap. Give it a shot.

I also build according to instructions and parts, and make sure it works before trying out any mods. But then I am a Noobie.

Good luck

[Ardric]

The voltages on Q1 to Q4 don't look that off to me.  Q5 is obviously not biasing correctly.

When the source resistor is relatively big, like the 5k6 on Q5, I've had difficulty getting really gainy JFET's to bias.  Is Q5 a J201 by any chance?  Perhaps you could try a few different JFET's in that spot.  Also confirm once again the 100k trimmer goes all the way up to 100k when Q5 isn't in circuit.

You could try swapping Q2 and Q5 and check the voltages again.  Q2 seems to have a higher Vgs if I'm reading the voltages right.

I built RG's FET matcher circuit and sorted out all of my bags of FETs, so when I built the BSIAB2 I picked a lower gain matched pair for Q1/2 and a couple of really hot J201's for Q3/4.  I used an MPF102 for Q5.  AFAIK this circuit doesn't need FET matching, but I loved the sound from first power up, so I've left it as is.

[erick4x4]

I had my 2nd BSIAB build kick my butt during Easter. For me it was discovering a bad solder joint on a cap. I must have stared at the board for hours until I finally saw it. This is after desoldering many many parts that I thought might be defective!

I did a search for BSIAB here and read every thread I could find to see if anyone was having the same problems as I was. And there was on guy that did, and it was a bad solder joint on a cap. Give it a shot.

I also build according to instructions and parts, and make sure it works before trying out any mods. But then I am a Noobie.

Good luck

Yeah that's how I feel. I have just stared at it.

So the fact that I have output with tone control (and very low), and absolutely no distortion or drive, does that give anyone an idea of where to start? Ahh!!! I resoldered all pots today, I also resoldered everything going to ground. I guess next step is resolder every joint? Is a bad part (or wrong part) sound possible? I have looked a dozen times but still am going at it!

No quitting for me. I loved my first one, but gave it to a guy a church. Now that I have implemented the low mid control, and high mid boost, I am so excited. Must fight on . . .