Help needed with big Muff build - very low output?

[Awblaster]

Hey all, new to the forum, new to building pedals, so as you can probably guess, I've got a problem!

The build I'm working on is a pedalparts.co.uk Big Muff Pi. Kit info/schematic is here: http://pedalparts.co.uk/docs/BigMuffPi.pdf
I'm building a Black Russian one, with the flattened mid-range option (R18, R19, and C10 changed).

I've currently got the build at the stage shown on the "Test the board" page in the .pdf (so no switch wired in yet). I'm getting a signal through, and the pots all work when they're turned, but the overall signal is very quiet.

Pictures, of the back of the board:

http://i62.tinypic.com/otjltl.jpg

And the front:

http://i58.tinypic.com/2s63613.jpg

Hopefully those'll be enough to spot a problem.

I'm hoping that it's something really obvious that I've just missed due to not having built any stompboxes before. If it's not something immediately noticeable, what should I be checking to work out where/what the problem is?

Cheers!

[Mufftastic]

This might be a dumb suggestion but are you sure the transistors are in the right orientation.  My bc550 transistors are reverse pin order from my 2N5088 ones.  When I've out them in backwards I got low output.  Worth double checking the pinouts.   

My second suggestion is to rig up an instrument cable with alligator clips and then you can test after each transistor stage to see where the problem is. 

[LucifersTrip]

it's all guesses without voltages...a low output (if everything else sounds good) can be miswired in/out jacks...

[R.G.]

Hey all, new to the forum, new to building pedals, so as you can probably guess, I've got a problem!
...
I'm hoping that it's something really obvious that I've just missed due to not having built any stompboxes before. If it's not something immediately noticeable, what should I be checking to work out where/what the problem is?

Yep, as you expected, you're not the first to run into issues with a first pedal. A large fraction of all the pedalbuilders in the world have come here to get started over the years.

So there are some well worn and tested ways to deal with this. You've had comments on a couple of them. But the best thing to do is to go read "Debugging thread: what to do when it doesn't work", which is a sticky post that's just in front of all the new posts that come in. It outlines what is probably the best and fastest way to debug a problem by telling you the information to tell us so we can help you.

Pictures of boards are not all that much help for spotting specific problems other than beginner soldering mistakes, and the crudest of wiring problems. The vast - vast - majority of problems are wrong component/value placed in the board, wrong/backward pinout issues, wiring errors, and soldering problems. However, solving these issues is fastest if you can get out a voltmeter and follow the instructions in "what to do when it doesn't work".

Notice that it says "when it doesn't work", not "if".  We have all had issues.   

[aron]

As R.G. said, Debugging page. But really - if you had an audio probe, you could isolate the problem stage within a minute or so by "probing" the various stages.

[LucifersTrip]

Hey R.G. & aron (and probably others)...

I'm surprised you guys missed it since I've posted that pic a hundred times already, but it does actually take you to THE debugging
thread when you "click here"

[aron]

Not that debugging page, this debugging page :-)
http://www.diystompboxes.com/wiki/index.php?title=Debugging

[LucifersTrip]

??

But the best thing to do is to go read "Debugging thread: what to do when it doesn't work"

As R.G. said, Debugging page.

[Awblaster]

Cheers for the advice and links! Built myself an audio probe, and I've managed to narrow down the problem to Q4 - up to there, everything's at a nice loud volume, but it drops at that transistor. So, the voltages for that:

Q4
C: 9.08
B: 1.4
E: 0.9

Any ideas now? I tried swapping in a new transistor, but the sound and voltages are the same. Any other voltages I should be looking at, or are there any other parts I should swap out?

Thanks for the help so far!

[LucifersTrip]

double-check resistors values and solder joints surrounding Q4

[bluebunny]

R24 shorted?  Your collector voltage is on the +ve rail.