Help debugging BSIAB

[phil]

I just built this BSIAB on a perfboard based on the BSIAB layout at General Guitar Gadgets (http://www.generalguitargadgets.com/pdf/ggg_bsiab2_sc.pdf) and there's no sound at all so I've been trying to debug it for about a week and I'm stumped, so I'd really appreciate any help at all. So far this is what I've done:

1. I've used a yellow highlighter to trace all the connections and verify.
2. verified that all 3 polarized capacitors are oriented properly.
3. Checked the battery voltage (8.4)
4.Taking the voltages at all the transistors(which I've listed below) - they look right to me.
5. I've built an audio probe and found that I can hear sound when I probe between r2 & q1, which is the Gate of q1, but there is no
sound at the Drain of q1.
6. Since the voltages of q1 look right to me, I replaced q1 with another 2n5457 and retested, but get the same results.

I'm really stumped as to how I would have sound at the Gate of Q1 and absolutely no sound at the Drain of Q1 when the voltages look ok. Anyone have any ideas?

Schematic: http://www.generalguitargadgets.com/pdf/ggg_bsiab2_sc.pdf
built on perfboard. verified pinout of 2n5457 and j201
No sound at all past Q1

Voltages
Q1
Actual/reference
g - .02 / 0
s - 1.3 / 0.95
d - 5.42 / 4.5

Q2
Actual/reference
g - 3.8 / 3.8
s - 5.42 / 4.5
d - 8.0 / 8.0
Q3
Actual/reference
g - .1 / 0.3
s - .38 / .75
d - 4.1 / 4.3
Q4
Actual/reference
g - 3.83 / 3.8
s - 4.1 / 4.3
d - 7.9 / 8.0
Q5
Actual/reference
g - .1 / 0.5
s - 0.9 / 0.9
d - 3.5 / 3.

I'm going to continue double checking that everything is hooked up correctly, but it looks like I never make it past the first stage, even though the voltages look right and I've swapped out the transistor.

Thanks in advance for any help you may have to offer ...

[John Lyons]

The voltages look good.
You may have a solder bridge somewhere that's shorting out the signal.
Get a pair of strong reading glasses at the dollar store if not a 10X jewlers loupe and make sure you don't have any stray connections where they should not be. It doesn't take much to stop the signal.

Check the jacks, switch  and other connections as well.
Take a break then a deep breath and grab your highlighter and a fresh unmarked layout and go slow, it's most likely something you overlooked and is really simple.

John

[petemoore]

  Finding a bad cap is rare [electrolytics win this race].
  Lift the cap on the drain that isn't producing sound, then test drain output again, using your probe that has a DC blocking cap...

[Rafa]

Is Q1 ok?
.02/0?
Cheers
Rafa

[phil]

Is Q1 ok?
.02/0?

I've replaced Q1 with another 2n5457, but didn't check the voltage again after the swap. I'll Check again to make sure it's 0 instead of .02 - I have a third 2n5457 to try as well, but what might be better is if there is a way to test the transistor to see if it's okay. I've never worked with transistors before, so this would be a useful thing to learn ... can anyone give me some idea how to do this without special equipment?

You may have a solder bridge somewhere that's shorting out the signal.
... make sure you don't have any stray connections where they should not be. It doesn't take much to stop the signal.

Take a break then a deep breath and grab your highlighter and a fresh unmarked layout and go slow

Thanks for confirming the voltages and your suggestions. Although I've gone through everything with a 10x loupe and rechecked everything with 2 fresh layouts + highlighter, I'll do the same excercise but with a dvm to check for shorts.

  Lift the cap on the drain that isn't producing sound, then test drain output again, using your probe that has a DC blocking cap...

Thanks for your help Pete - There are actually 2 caps (C2 & c4 on the ggg schematic) and the source for Q2 connected to the drain of Q1, so I pulled the drain from Q1 from the socket and probed it - there's no sound at the Q1 drain doing this either, but still theres sound at the Q1 gate. Not quite sure if that's what you meant though - I've never used an audio probe before so I may not be probing the circuit properly. Did I need to desolder C2 and/C4, leave Q1 completely hooked up in the socket and probe for sound at the source of Q2?

[John Lyons]

You should be able to get sound on the drain either way. Just puting the audio probe on the drain should produce sound.

John

[phil]

You should be able to get sound on the drain either way. Just puting the audio probe on the drain should produce sound.

John

Thanks for the info John! That was VERY helpful  as it validated that I was using the audio probe correctly so I could confirm that the problem (well, the first one anyway) is right at Q1 - there's not much point in going further down the circuit if no sound is getting past Q1.

So focusing on that, I replaced the 2n5457 with a new one and remeasured the voltage and got basically the same readings and again it didn't work so I checked the orientation of the transistor against the layout I was using:

http://www.generalguitargadgets.com/pdf/ggg_bsiab2_lo.pdf

It looked right (flat side facing right, which should put the drain at the bottom) So I tried a J201 and got the same result.

Finally, I put in another 2n5457 but in the other orientation - I've got sound now at the source of Q2 as well as the top and bottom pins of Q1!!!  I was already late for work, so I couldn't continue debugging    - I'll have to continue this weekend, but I must have all the transistors flipped. Looking at the layout above it sure looks like the flat side of Q1 should point to the right to get the drain at the bottom, but I must be reading it wrong. I am a total newbie with transistors so I apologize for wasting your time .

Anyway, I'll post my results once I get time to debug this weekend, but now that the sound gets past Q1, I can use the Audio Probe to work my way through and that should help me get the board working.

Thanks to everyone for your help and suggestions - this is the first effects pedal that I've built so it's really great to have your help!

[petemoore]

http://www.generalguitargadgets.com/pdf/ggg_bsiab2_sc.pdf
  J201's print, when in a cct. board or socket, will face < or like
  l)
  Drain on top. Gate on bottom.

[phil]

Well I did finally get my bsiab working!    after flipping Q1 around, I did get sound at the source of Q2, but when I later checked the voltages on Q1 they were all wrong, so the original orientation of the transistors is correct. I replaced Q1 with a fresh 2n5457 as it did not survive the pinout reversal, but as expected, still no sound at the source of Q2  . Since I had already visually checked the circuit against the layout 3 times, this time I printed out the layout again, got the highlighter and went through the layout starting from the input with my DVM checking all the electrical connections. I found 2 cold solder joints - one at C3a to my ground bus, and another at C3b again to the ground bus. After reflowing the solder on both connections, I fired it up and was rewarded with a working first build (finally!). There's some noise issues to work out, but the BSIAB sounds awesome and I'm really pleased that I was actually able to debug the circuit and make my first build work!!!

In retrospect, this probably was a bit of a complicated project for a first build, but in a way I probably learned a lot of useful skills in being forced to debug it - the only thing I really wish I had done differently was to use a Vero board and a vero layout, which would have not only made the build less error prone, but would have ended up with a better end result - I'm sure that buying an rts would have made it a piece of cake, but I don't think I would have learned as much going that route since I don't plan on making my own pcbs. Also, the Vero layout makes it so much faster to build a project - I just built an Orange Squeezer and got it  working in about 3 hours using Torchy's Vero layout. Wish I had found his BSIAB layout before I started my build ...

I'll start a different thread to address the noise issue, but I did want to update the status on my circuit and thank everyone for their help in getting my first effects project working!