Meathead debug, please help before I throw it out the window

sickman82 · Post by **sickman82** » 09 Jul 2011, 17:35

Hi guys, still new to the forum and to the whole world of DIY pedals really. Go easy!

I've built a DAM Meathead clone from this vero layout - http://3.bp.blogspot.com/_y7gcfRKQFgA/T ... 710238.png

I thought it looked easy, and as my last build was a Big Muff that is exactly what I wanted.

I got everything wired up and was very excited to try it out and.... nothing. I'm sure you have all been here before, you build a pedal that you are really keen on playing with and it doesn't work. Frustration isn't the word. So, there is no bypass signal or effect when engaged. The LED lights up when it is on though, so power is getting to the board.. and I double checked with my meter. I checked my wiring, no problems that I could see but I thought that I might as well try a different wiring diagram, just in case. Still nothing. I checked for continuity from the input tip, followed it through the switch to the output tip and there is continuity from input to output. I am about to revert back to the original wiring diagram that I have used for all my builds so far, from madbeanpedals.. and tidy up my solder joints etc.

The only thing that I can think is that I have wired up the jacks wrong somehow.. I'm using Switchcraft 'style' enclosed stereo switching sockets which have a total of 5 lugs - ring, sleeve, tip and two other lugs for switching. For the output I have connected the tip and ring to make it mono. From what I can tell though my wiring is correct, looking at my previous builds using these sockets they match up. So I'm stuck, very stuck. Debugging isn't something I know much about, but I think I need to learn because this is driving me mad.

I'll just rewire it to the madbean diagram and then test, if I still have no luck I'll post some pictures. Really, really hope one of you guys can help me out. Thanks.

sickman82 · Post by **sickman82** » 09 Jul 2011, 18:21

Ok, still no luck.. here are the pics.

First a top down shot of the guts, I know.. I used the same colour wire throughout, but I like the way it looks! Here is the wiring diagram I use.. http://www.madbeanpedals.com/tutorials/ ... ng_MBP.pdf

Second, the top of the veroboard..

Next the bottom of the board..

Here's the input socket.. (EDIT - In this pic of the input socket I have the ground from the board going to the sleeve of the socket - as per the other wiring diagram I tried out. It's now correctly soldered to lug 2 of the switch with no difference)

Finally, the output socket..

sickman82 · Post by **sickman82** » 09 Jul 2011, 18:37

Just been checking for bridges on the board with a loupe, none that I can see. But even if there were, it doesn't explain why there is no bypass signal. Also have now re-flowed all solder joints throughout the build and no difference. I have tested all grounds for continuity, all input and outputs for continuity and it seems fine. I'm losing my mind with this one! It just has to be something that I've cocked up with the wiring. on the sockets because they're so damn confusing with all their lugs!!

blackbunny · Post by **blackbunny** » 10 Jul 2011, 00:46

It looks like you have shorted out your output socket. Try removing one end of the short wire from the terminal that the long wire is also connected to, leaving the long wire connected.
You should now get both effect and bypass signals.

If all is good, you can solder the (now loose) end of the short wire to the other terminal, ie., connect the ring to the sleeve. Or you can remove it altogether - but only on the output jack socket.

blackbunny · Post by **blackbunny** » 10 Jul 2011, 06:14

This diagram may be easier to follow than my instructions!

sickman82 · Post by **sickman82** » 10 Jul 2011, 07:50

Thanks for your reply..

I've posted a similar thread over at diystompboxes, the guys over there spotted that mistake too.. they also said I'd need to send that ground over to the switch so that all grounds are connected.

In my defence, I was following the instructions from here ---> http://www.doctortweek.co.uk/shop/artic ... id%3D71%26

That's where I buy all my parts from.. I just assumed it was correct, as you would do. It clearly says that to make a stereo socket mono, you need to connect RING to TIP.. ooops!

I'm gonna give it a go now, I'll let you know how I get on.

Thanks again.

sickman82 · Post by **sickman82** » 10 Jul 2011, 10:28

Got it wired up correctly now, and I get a bypass signal.. but nothing when the effect is engaged. Any tips? I'm gonna have a look around the internet and see what I can find to help debug this issue but anything you guys can offer I would be eternally grateful! Need to clear my head before I do any more work on it!

sickman82 · Post by **sickman82** » 10 Jul 2011, 11:06

Update....

Checked voltages on the transistors and here's what I found:

Q1 - 2N3904
E=0
B=1.87
C=2.42

Q2 - BC182L
B=2.42
C=1.74
E=1.72

for the electrolytic capacitors.. (I just realised there are two)

47uf
+ = 9.26
- = 0

10uf
+ = 1.72
- = 0

When I'm probing the electrolytic caps, I'm keeping the black lead of my dmm on the signal ground and probing with the red on both + and - sides of the caps. When I put the black lead to the positive of the DC jack and probe I get -9.25 on the - leads of both caps. Not sure if I am meant to do that, but I did anyway and that's what I found.

DaveKerr · Post by **DaveKerr** » 10 Jul 2011, 11:48

Make one of these and probe away from input to output

sickman82 · Post by **sickman82** » 10 Jul 2011, 12:30

Ok, I'll give that a try tonight.. I think I've got some 100nf caps somewhere. Hope so anyway.

DaveKerr · Post by **DaveKerr** » 10 Jul 2011, 12:38

If you don't have a .1uF handy, .22 or .47 should work, anything non-polarized rated 16v or higher.

sickman82 · Post by **sickman82** » 13 Nov 2011, 16:27

Just as a follow up to this, I abandoned this and built Mike Livesley's layout for the Meathead. But, today I decided to dig it out and have a look. It turns out that instead of a 2N3904, I had a 2N3906 in there. I checked my baggy with the supposed 2N3904's, and guess what? They're all 2N3906's! Must have been picked wrong from Dr Tweek. Problem solved!