ggg big muff problem

[olslick]

  hi everyone. i'm having some problems with a big muff kit i bought from general guitar gadgets. the version i'm trying to build is the ram's head. when bypassed there is signal, but once you engage the effect you get nothing. there is some signal if you play with the pots, but very faint and clean. it's mostly white noise. the led works as well.

  i've looked over everything pretty closely as i've been working on this for two days now, trying to take breaks so i can come back to it with a fresh set of eyes. as of right now i can say that the wiring is correct. the diodes and transistors and all polarized caps are correctly oriented. i've gone in and cleaned any soldering that looks like it could have been contributing to a bad connection. being that i get signal in bypass, i assume the 3pdt switch is functioning correctly, as well as the input/output jacks. considering that the white noise i'm getting fluctuates while turning the pots i believe that they, too, are wired correctly and are making good connections. i would assume that since the led works, and i'm getting signal from a 9v power supply, there's nothing wrong with the dc jack wiring.

  there are a couple of places that look like they could be solder bridges, but the leads are so close together on the pcb, i'm having trouble getting rid of them. plus, the couple of instances where this is happening, there seems to be trace lines connecting the components on the pcb anyway, so i'm wanting to dismiss solder bridges as the culprit.

  the wiring diagram on the ggg website shows that c9 and c13 are polarized, even though the 1 uf caps they send you are film. so, i went and bought two 1 uf electrolytic caps and plugged them in instead as the bill of materials states you can use either or.

i do have a multimeter, but i just bought it being very new to this and have no idea how to use it. i will post pics but will probably not be able to do so until tomorrow. any help or advice anyone can give would be greatly appreciated. i try not to waste people's time with this sort of thing as it's usually a simple and obvious mistake but, i am thoroughly baffled by this one.
 

[oliphaunt]

I suggest you build an audio probe and go through the circuit.  This will tell you where the audio signal stops doing what it should be doing and then at least you know where in the circuit to look for issues. 

Also, use your MM to test for the correct voltage to the circuit board and verify the voltages on the pins of all the transistors.  The GGG web site has a page with voltages for a Muff, but be aware that in my experience (I just built 2 Muffs on GGG circuit boards and breadboarded them both first) that the Ram's Head may not have exactly the same voltages they post.  All of my builds have about 7 volts on the collector of Q1, which seems high, but all four builds were the same, I thoroughly checked them, and the circuit sounds great, so I'm worrying about it.

One of the pinned topics at the top of this board suggests ways to debug your build and all the info you should check for and post to get the best help the folks here can give.  Read that topic and try what it suggests.

[olslick]

  okay, using the multimeter with the black needle on the G hole on the pcb (which i assume is for ground), my results are as follows:
q1
c= 9.09   
b=0.09
e=0

q2
c=4.2
b=.66
e=0.08

q3
c=3.83
b=0.6
e=0.05

q4
c=4.13
b=1.86
e=1.14

diode values are:

d1
a=0.45
k=0.65

d2
a=0.65
k=0.45

d3
a=0.42
k=0.62

d4
a=.062
k=0.42

measuring the where the red wire connects to the board from the 9v power adapter, i get 9.37. black wire gives no reading.

  the ggg ratings can be found here http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=108&Itemid=26

if i'm measuring correctly, i'm clearly not getting the readings i should. but i don't know what this could mean as far as isolating the problem(s).

[olslick]

here's some pics...

http://i295.photobucket.com/albums/mm149/olslick/P1013042.jpg
http://i295.photobucket.com/albums/mm149/olslick/P1013040.jpg
http://i295.photobucket.com/albums/mm149/olslick/P1013021.jpg
http://i295.photobucket.com/albums/mm149/olslick/P1013044.jpg
http://i295.photobucket.com/albums/mm149/olslick/P1013040.jpg

[oliphaunt]

Here are the values from my transistors from my working Rams Head.  Most of your measurements seem within an acceptable range to me, except your Q1 seems the most out of whack.  I'm not a particularly experienced builder so I don't have too much help to offer, but maybe this will help you see something... 

Try that audio probe, it's super easy to make (1 cap and a jack)  and is an invaluable tool for finding problems.

Q1
C=7.04
B=0.59
E=0.02

Q2
C=5.5
B=0.65
E=0.04

Q3
C=3.91
B=0.67
E=0.04

Q4
C=4.91
B=1.31
E=0.78

[olslick]

how does the signal tester work? i've seen how they're built, but beyond that i'm not too keen on how it will help me. from what i understand, i use it to probe stuff. i'll get a beeping sound until i come across the part thats not working? can someone explain this to me? please be very detailed and descriptive as i'm fairly new to all of this.

[oliphaunt]

My audio probe is nothing more than a .1u capacitor with one lead soldered to a 1/4" jack and the other lead sticking out.  The capacitor is soldered to the jacks' tip (signal) connector and a wire from the sleeve (ground) connector is connected temporarily to ground of your circuit.  This capacitor act as a decoupling cap to keep voltage from getting into the signal, think of it as the output cap in a circuit, so that you can touch the free lead of the audio probe capacitor to any point the circuit.  Plug a cable into the the jack and then into an amp.  Now just follow the signal flow and touch the lead of the probe to the components on your circuit board while you strum a guitar connected to the circuit (or send it some other constant sound).  You will be able to hear what is happing at any point in the circuit, and so you will be able to tell when things don't sound right.   (Be aware the sound may pop and crackle as you touch the lead to various things, so don't turn your amp up loud.)  In your case try first touching the probe to the collector of each transistor.  If one of them is not working you will not hear any guitar sound at that point.  Using the probe just go through the circuit from the beginning, and see what it sounds like at each point.  The problem area should bebcome obvious, and you will have at least narrowed down some possibilites.

Here is another explanation I found using the search function: http://www.diystompboxes.com/pedals/debug.html

Oh, since it hasn't been mentioned yet, double check your transistor orientation, that's probably one of the most common cause of problems!  

[olslick]

i'll give it a shot...

i have to assume the transistor is oriented correctly. it matches the outline on the pcb and it's positioned the same as the other ones, which have close to average readings.

[oliphaunt]

I meant check all the transitors, not just one, but it seems likely they are oriented correctly given the voltages you measured.  However never just assume they should go in the same direction as the diagram!  You can easily tell in this circuit by looking at the schematic and matching the components against the PCB layout.

[olslick]

yeah, this audio probe is frustrating. am i supposed to re-solder everyplace on the board that doesn't sporadically make my amp pop?

[Tony Forestiere]

No...every time you touch the probe it will probably  pop. Once that is over and you have a solid "stick", you should be listening to the differences in your sound in the audio path before and after the component being tested.
You will figure it out

[olslick]

okay, i think i've figured it out... the audio probe that is. and i've found that i stop getting guitar signal after the second leg of c15, before where it goes to r26. i popped it out and flipped it around to see what would happen (it's a ceramic cap so not polarized) and it's doing the same thing.

what is the likelihood that this cap is faulty? is it possible that if it's faulty, i would still get signal out of one leg? is it possible that i could still hear faint guitar signal running through the pedal to the amp, but the signal stops at this c15 cap with the audio probe? could this faulty cap cause q1 to give screwy readings?

[olslick]

the schematic on ggg says that c15 is optional, so is r26. so thinking that c15 wasn't functioning properly, i took it out along with r26. now i get nothing from the audio probe. nothing at all.

[oliphaunt]

You are right that C15 and R26 are optional.  They will not effect the basic function of the circuit even if they are missing.  So if you removed them that's fine, just move along from there.  You mention that you didn't hear signal on the second leg of C15.  One leg connects to ground, so you wouldn't hear anything on that end since you are grounding out your signal. You would onoly hear the signal on the end of C15 that splits off of the main signal path.  Same for R26.  For starters, only check along the main line of the signal path, not the various resistors running off to ground and +9v, or in the feedback loop of the transistors, as these may be confusing.  If you get signal sounding like it should at the transistors then those things are probably doing what they should.

You should try touching your audio probe all along the signal path, starting with the input to the circuit board. Make sure the very first connection to the board has signal and follow the schematic from there.  It is sometimes difficult to follow the schematic as the signal it travels along the PCB, but the GGG parts layout page will help you.  Follow the traces and pay attention to which end of the components you are testing, keeping in mind what you might expect to hear after each component.  

Assuming everything is ok up to that point you should hear a fairly weak signal at the base of Q1, then a stronger signal at the collector.  The signal at the collector may be somewhat muffled by the filter cap C2 in the feedback loop (I prefer to remove this cap completely).  Each transistor will repeat this pattern, a weaker signal at the base and louder signal at the collector.

[olslick]

so is it not good to jumper the parts i took out? cause like i said, now they're out, and jumpered, and i'm not getting any signal at all from the probe.

[oliphaunt]

You need to remove the jumpers.  By jumpering those components you have directly connected the guitar signal to ground, shorting it out so you will get no sound anywhere.

[olslick]

i'm losing signal somewhere between r1 and c1. i took c1 out and flipped it around to see if i could get signal and i did out of on leg. i got nothing from the leg that connects to q1. when i soldered it back in, it went back to doing nothing from both legs. i'm using an aluminum electrolytic here. could this cap be failing? i kind of doubt it is, but short of cold joints and bridges i don't know what i'm supposed to do here.

okay no signal between r1 and c1.  joints fine.  no bridges.  now what?

[oliphaunt]

i'm losing signal somewhere between r1 and c1. i took c1 out and flipped it around to see if i could get signal and i did out of on leg. i got nothing from the leg that connects to q1. when i soldered it back in, it went back to doing nothing from both legs. i'm using an aluminum electrolytic here. could this cap be failing? i kind of doubt it is, but short of cold joints and bridges i don't know what i'm supposed to do here.

okay no signal between r1 and c1.  joints fine.  no bridges.  now what?

Assuming you removed the jumpers from C15 and R26, you should have audio signal on both legs of R1 and C1 and at the base of Q1.  If you don't double check the orientation of C1.  Even if it is backward or has failed you should have signal on the leg of C1 closest to R1.  If you don't you will need to check the joints and traces.  You can also check continuity with your MM to make sure there is a connection between the components but no direct connection to ground.

[olslick]

now all of the sudden i'm getting signal out of c1 over to q1, where i only seem to be getting signal from the collector and base. the signal gets a lot quieter as i go down the circuit path. is it supposed to do that?

[olslick]

i'm getting to the point of extreme frustration.