Vulcan Rat Creation

[jfrabat]

Started checking with the audio probe.  Signal comes in strong to the board.  Becomes a bit faint by the time it reaches Q1 base, but it is REALLY faint by the time it comes out of Q1 emitter.  I can still track it to Q2, but I cant hear anything by Q3. 

Here's the board.  Not my best work by far, but I always have a hard time with perf boards!



The middle pot I had to put off board because it did not fit right.   Anyway, I only got big boxes left, so real estate is not an issue....

Oh, and I get no light from the LED...  I think I roasted it, cause its getting 9V!

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[robthequiet]

For starters, I might suggest desoldering the pots and thoroughly cleaning the perfboard of any remaining solder residue, then try to operate the pedal with the pots off-board. Separate the mechanical issues from the electronical.

Would it be possible to upload a photo of the top of the board? -- then we can magically overlay both with photoshop and see how the layout works.

[jfrabat]

Here's the top.



Ignore the positive lead that I just borke off taking the picture...

Basically, it is the same layout that's here:



And here's the schematic:



The voltage protection is not in the schematic, and the diodes are in the bottom square sticking out of the bottom.

[Ben Lyman]

The layout works, I have confirmed that but sorry I didn't post my reverse bottom trace layout for you:

Hard for me to tell for sure but maybe you don't have the tone pot quite right yet.
Also, notice how I numbered the pot lugs so the middle pot (tone) is actually upside down and goes under the board when installed.
There's a lot of quirky details that I often leave out like my LED is a superbrite clear blue and will shine plenty with a 47K on it.
If you are using a diffused LED, you probably need a much smaller value r on it.

[robthequiet]

Visual aid:



You said that the signal seemed weak at Q1 emitter -- what about the collector? What are the voltages on the transistors now?

[jfrabat]

Anyone see any solder ridges I am missing?  Or other errors?

[robthequiet]

I was looking through the solder side and there are some spots I'd like to check out. Ben mentioned the tone pot. Was lug 2 OK? I would like to see the voltages on the transistors too, but there area a few solder joints and lead dress items that caught my eye. I am not sure if I am reading the layout properly, but is R10 in the right place?

[Ben Lyman]

if R10 is there, maybe it's hidden by the caps.
can't tell for sure but check where I circled in blue for a solder short.
Also, take your output wire right from the center lug on the volume pot. I've read lots of warnings about trying to solder to those rivets so I've never tried it but maybe won't pass a signal.

[Cozybuilder]

This RC filter calculator will allow you to choose components for your desired frequency knee:

http://www.experimentalistsanonymous.com/ve3wwg/doku.php?id=rc_simple_filter

[jfrabat]

The layout works, I have confirmed that but sorry I didn't post my reverse bottom trace layout for you:

Hard for me to tell for sure but maybe you don't have the tone pot quite right yet.
Also, notice how I numbered the pot lugs so the middle pot (tone) is actually upside down and goes under the board when installed.
There's a lot of quirky details that I often leave out like my LED is a superbrite clear blue and will shine plenty with a 47K on it.
If you are using a diffused LED, you probably need a much smaller value r on it.

That diagram looks very different...  But you did give me an idea; when I checked this:



And superimposed the traces:



And compared it to this:



I noticed some differences here:



So I at least know where to start looking...  I'll report back when I fix those.  I doubt the middle pot is the issue, as only pins 1 and 3 are connected (the bridge to pin 2 is in the board), so the effect of wiring them wrong would be the knob turning backwards, but it should still work, right?

[jfrabat]

That was not it...   But something else is loose.  I noticed that LED is flashing.  I think its somethung in the switch, but I will have to check.  But there is still no sound.

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[Ben Lyman]

I always reverse the trace diagram, that's why it looks different because it's a mirror image. That way I have a picture of the top of the board and all the components and I also have a picture of what it looks like when I turn it over.

It is important to hook up the tone pot wiper but a quick way for you to do this is to attach a short wire right to the pot itself, connecting lugs 1 and 2

EDIT: WHOOPS! you're right, that is way different. Must be one of my rough drafts, I'm afraid I might not have a reverse image of my trace, sorry about that, my bad 

[Ben Lyman]

Great job troubleshooting, I think you nailed it. Check that one spot on the power line that I circled too, fix the others and connect your tone pot lugs 1+2 together and it should be ready to go.

[jfrabat]

OK, fixed the positive link and added the wiper jumper, on top of the above mentioned fixes.  This is the PCB as of tonight:



I have noticed a significant drop in sound after D1, and even more after Q1.  Just a tiny bit of sound is making it to A1M.  And almost nothing makes it to D2.  I am using 4001 diodes, in case that's an issue...  Got tons of others if I need to change this.  Look at the video below for the audio probe test.  The phone did not capture the tiny amount that made it to A1M, but it is there.  including the layout for reference.





Any ideas?

[jfrabat]

Aha!  Is it me, or are all my diodes backwards???

Please confirm, but I think they are...

[robthequiet]

Diodes look good to me, but I can't really tell with the red led. Have I missed it or do you have voltage readings for the transistors?

I am wondering if Q1 is amplifying at all, maybe the voltages will help us make sure it is biased correctly.

[Ben Lyman]

Ya, the diodes look right. check here next, it looks like it might be bridged where it shouldn't be

[jfrabat]

Made progress tonight.  I found a short in the input jack  (i had all my attention on the board and did not check the jacks!  One of those DUH! moments...), and fixed it.  It seems that was causing a bad ground, which is why the LED was not lighting up as well.  It is lighting up now, though (but I will also re-wire it, because it lights up even when the pedal is bypassed).  Now, with the audio probe, the signal makes it all the way across to the circuit output (including the output jack) at about the same volume level as it was coming in.  I did not check the output jack to see if it is also shorting with the plug connected, but I will tonight (I just thought about that one, and maybe that's causing no signal to reach the amp).  Anyway, I took the Q voltages.

Voltages:

Battery: 8.92

Q1:
E:163mV
B:733mV
C:7.20V

Q2:
E:0V
B:332mV
C:8.71V

Q3:
E:178mV
B:752mV
C:7.13V

For some reason, though, no sou d comes out the amp when I connect the circuit (it does sound when I bypass it).  I am truly stumped now!

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[robthequiet]

I think the transistor voltages are within range, probably Ben can confirm -- Do the pots do what they are supposed to do?

[Ben Lyman]

Just checked my volts, all are 2N5088 so maybe a little different.

Battery 9.4v

Q1
c 4.70
b 1.01
e 0.43

Q2
c 4.60
b 1.02
e 0.44

Q3
c 4.69
b 1.01
e 0.44