Trouble with Big Muff Pi

[Radamus]

Hi. I'm on my third pedal now. I think I've had problems with each one so far, but this is the most complicated and the hardest for me to diagnose. I made the big muff pi from http://www.diystompboxes.com//pedals/triangleMuff.jpg. I'm not sure why I chose that one, but it's the only one I have the parts for.

It's my first breadboard project and I had to fix a few errors that had to do with not knowing how to use a breadboard. Now, I have all the pieces on the board and, as far as I can tell, in the right order. The problem, and this is similar to the problem I had on my Bazz Fuss, is that I get sound, though faint, from the pedal when there is no current in it. When I disconnect the battery, it makes some fuzzy sounds that are really quiet and I lose the high end. No big deal, though, as it is supposed to run off of a battery. When there is current, I get no sound whatsoever.

I checked all of my transistors (2N5089's) and they are now correct (or thereabouts) to what I read in other forums. I had to let two of them go in the process. None of the wires seem to be touching. I did not clip the leads, but there are gaps. Nothing is shorting unless it's jumping across the gap. I do get sound when I have no battery, which leads me to believe that the input and output plugs are just fine. Every part seems to be getting current.

As a note, I followed that schematic, which isn't exactly specific all the time, as much as I could. The 1k resistor I forgot to order, so I used a 2.2K. I'm using 1N914 diodes and 2N5089 Transistors. None of my capacitors are polarized, though the picture seems to call for two. There, again, it is inconsistent. I couldn't get a 500pF Capacitor, so I used 680pF instead. The 0.004 uF capacitor (I'm assuming it's uF) I replaced with 0.0047. As far as I can tell, I wired up the potentiometers and jacks correctly. I'm pretty sure I grounded everything correctly, though the wires that I soldered to the jacks and pots are copper strand, so they don't completely fit in the hole.

It seems bizarre to me that this pedal can make some fuzz sounds without current, but that it then fails to make any sound when current is supplied. Is this a dead capacitor type problem? Are my transistors not amplifying? What's killing the sound?

Thanks in advance.

[michal_k]

are you sure you checked how rows of your breadboard are connected? If that's not the case try looking for broken jumpers, solid core wire are easy to break.

if i were you i'd also check orientation of the transistors once again. use datasheet.

[sshrugg]

I had problems like this when I tried breadboarding a fuzz face for the first time.  It turned out that, because I didn't trim the leads of my components, some of them were touching in places they shouldn't.  The circuit got bent in such a way that I had no output.  I'm sure you've checked this already, but I thought I might mention it.

[Radamus]

I'm in a similar situation. I did not trim the leads and I worry they may be too close, but it doesn't look like any are touching. I didn't want to clip them because I only have so many parts and I don't want to perfboard it without the leads to connect. I think I might just have to start over. I'm not sure I can diagnose the problem, so I might just want to expand the project onto more space so I can keep it neater. It's also possible that the breadboards are old and dead or something. It's just weird to me that it works with no current (though quietly and it drops the high end) but the current cuts the sound.

[petemoore]

DEBUGGING - What to do when it doesn't work
  Best thread ever.
    That and just putting that DMM through the paces, a testclip DMM lead can be attached to a ground and then the probe lead can do much work with various dial settings, or the testclip can hold a probe tip or otherwise contact testpoints in a circuit such as a resistor lead.
  Testing for no shorting condition between battery clip lugs is ritual for new circuit pretest, that and testing that all grounds are common can be done with clip and dial left in beep mode [diode tester].

[Radamus]

I have read the debugging post and I thought I gave enough information. I remade the pedal on a different breadboard with more space. Nothing is shorting. I have the exact same problem. Once I apply current, I get no sound. So it has nothing to do with the construction. It's either parts or mistake I'm likely to make twice. Here's the read out:
Clockwise:
Q1
C=7.53
B=1.89
E=.35

Q2:
C=7.52
B=1.76
E=.23

Q3:
C=7.63
B=7.09
E=.95

Q4
C=7.58
B=7.01
E=.18

Diodes (left to right, starting with the one that goes right, then the one that goes left)

D1
A=6.98
K=6.73

D2
A=6.73
K=6.98

D3
A=7.09
K=6.89

D4
A=6.89
K=7.09

Potentiometers (knob upright from left to right, completely open)
P1
A:8.45
B:8.37
C:8.27

P2
A=8.45
B=8.37
C=8.36

P3
A=8.45
B=8.38
C=8.37

Battery at 8.95

I'm not sure how much more information is needed. There's so many resistors and capacitors, but I suppose I can tell you those if needed.

Is there any particular way I need to connect the grounds or is it sufficient that they all be connected together somehow?

I can take a picture if I need to. And the Transistor voltages are completely different on this new build. I checked the official manufacturing data on the transistors, so they are positioned exactly correctly.

Is it weird that it makes fuzz sound without electricity and that it makes no sound with electricity?

Please guide me.

[killerkev]

I never used breadboards so I give any advice on that. But I can tell you that the voltages on the collector of Q1&2 are very high. On Q3&4, they are still high along with high base voltages. They are so close that these transistors are probably not even working. Hopefully Petemoore will reread your post and give you more insight since he is very helpful.

[Radamus]

SO I've had this thing sitting here for a few more days. I've tweaked the capacitors, I've thoroughly checked the voltage. I even built a sound tester thing out of an old guitar cable, some wire, and a capacitor. This device does not seem to work for me. I checked it and all of the connections are there and functioning, but it doesn't work. I attach the ground section to the ground portion of my breadboard and I touch the capacitor to the parts. No sound. Not even at the input jack.

Can anyone give me some more recommendations to try?

[Meanderthal]

 The tranny biases are wacky, especially q3 & q4. Something not right there. At least your emitters seem about right. Are your trannys in backwards maybe?

The pots are all wrong. For instance, where is the ground (0v) for your volume?

I think you must still have the breadboard rails confused somehow. After all, it can't be a solder bridge, can it?

[Radamus]

I'm not sure what you mean by that. The transistors do not seem to be in backwards. I checked them and replaced them so that they all follow the C=8+, E=B-.5 rule that I read somewhere else. As for the rails, I have one that's hot and one that's not. I'm a little confused though as to which one carries that sound. I built a functioning  sound checker now and the problem I have is that I get sound coming out of that first transistor, but then it goes into a 10k resistor to ground. The sound goes into the 10k resistor, but I get nothing on the way out.  Is this a grounding problem? Am I even supposed to get sound out of the transistor?

I get confused on the nature of sound waves versus electricity. It seems to me that sound will go through the circuit no matter what, but the output slowly loses volume, so electricity is used to power components to amplify, such as the transistors. As for the path the sound follows, I have no idea. Does it all go into the ground? If so, how should I connect the ground to make sure that the sound gets through rather than being lost in the ether as it seems to be right now. 

The pots are all wrong. For instance, where is the ground (0v) for your volume?

As for the pots, I'll admit I have no idea what I'm doing. If there's something wrong, let me know and I'll try to fix it. Also, these breadboards are pretty funky. They might not be fully functional.

[Meanderthal]

 OK first, there is no 10k to ground anywhere in the schematic. There is a 1k from lug 3 of the sustain pot to ground though, and there is a 10k to positive on the second gain stage.

Audio should not be running through the positive nor especially negative rails at all.  You should be able to hear sound from each transistor though.

By backwards, I meant which way the flat side faces. Some manufacturers can fool you that way sometimes. If you have a DMM with transistor tester, that'll show you which is E,C,B.

As far as the rails, there are usually + and - on the outer edges and down the center. Then the regular connections are usually in rows, 5 or 6 holes on each mini rail.

Lug c on the volume pot connects to ground, right? Ground should read 0v. For that matter, you shouldn't get DC at all on that pot because of the decoupling cap.  More to the pot measurements than that, but that one's pretty obvious.

There is alot wrong with the measurements you got. It's not just one little problem, it's all weird. That's why I think it has something to do with your first use of a breadboard, easy to get it all mixed up.

Really, the BMP isn't all that complex. If you're familiar with other building methods, maybe give that a shot, one gain stage at a time. If it's all connected right, it'll work. That is NOT a bogus schematic. As for the breadboards, maybe try something simple like a Bazz Fuss to get a feel for it first.

[Radamus]

I meant 100k resistor to ground. From the looks of it, the emitter of each transistor is connected to ground either immediately or after a resistor. Yet, sound comes out of the emitter on that transistor, so how is that sound supposed to get back into the circuit. That's what I'm asking. Or is the sound not supposed to go anywhere? Here's another reason I might be an idiot, but it's CBE from top to bottom on the schematic right? If not then I'm probably backwards. This is something I thought I knew.

Thanks for your patience. I know I'm probably pretty ignorant still.

[dxm1]

but it's CBE from top to bottom on the schematic right?

Yes, on that schematic, the transistor collectors are at the top, bases in the middle, and emitters on the bottom. You said that you got your audio probe working? Then we can trace the signal one stage at a time...

First, apply a signal to the input (your guitar, a CD player, etc.) Touch the audio probe to the tip of the input jack, you should hear your signal. If so, then touch the probe to the base of the first (upper left) transistor. You should hear signal, roughly the same volume. If that works, touch the probe to the collector of the same transistor. You should hear signal, louder this time. If all of that works, you can say the first stage at least isn't totally dead, and move on th the next one...

[petemoore]

  the transistors are EBC with legs down, print facing you.
  that means they 'face the output if you have the ground along the bottom and the V+ along the top.

[Radamus]

I decided to scrap the breadboarding idea and I'm soldering it now. Chances are I'll never know what was wrong, but I sure as hell won't be using that breadboard again. Just curious, though, when you're using the transistors as amplifiers, which end does sound go in and come out?

[aron]

into the base, output from collector.

[Radamus]

into the base, output from collector.

Now it makes sense. So I decided to just solder the whole thing. It took me quite a while and was pretty complicated. Now, every transistor has the same value across all three parts. It's like 8.4 everywhere. There don't seem to be any solder bridges. How can I fix the biases? Are the transistors fried?

I checked the last one which has a base that connects to a 390k to hot and the voltage on both sides of that resistor were identical. Is this wrong?

Thanks for sticking it out with me.

[Radamus]

I checked the sound for the first transistor and it gets sound at the base, but none comes out at the emitter or collector. It's also getting (from battery to each point) around 8.4 volts to base and 7.8 to emitter and collector. This doesn't make a whole lot of sense to me. It's supposed to be much smaller at the base and emitter, right? And that seems to be the case for almost all of the transistors (which were ordered from this site, by the way). I've replaced the first and last ones and no change has come about, so I doubt that they're broken. I also cannot see any solder bridges where there shouldn't be any. WHat could be the problem here?

Is voltage supposed to be maintained throughout the project? I understand voltage drops, but resistors resist current, not voltage, right?

I really thought I understood this stuff.

Please help me out. I want this thing to work and I have no idea how to fix it on my own. None of the solutions I've read seem to work.

What information can I give you guys to help out? I'm looking to fix the first gain stage right now.

[petemoore]

but it doesn't look like any are touching.
  Not to say they Are touching anyway, but "I can't believe they were touching, they looked separated enough", is common enough to make visual observations ~moot.
  What information can I give you guys to help out?
  This: Make the board match exactly the schematic, in every way.
  All connections are common to board and schem.
  All NoN-connections are also the same as shown on paper.
  Resistance from Q1 base to V+ is exactly the same [within ~10%] as shown.
  I'm looking to fix the first gain stage right now.
  Count the # of connections at each node, be able to measure exacty that on the board.
  By now you should be able to whip the DMM around stage 1 measureing
  Base to Collector Resistance
  B to Gnd. R [best test-measured from battery clip, no battery]
  C to V+ R   [best when test-measured from battery clip]
  C to B Resistance
  E to Gnd R [while there, check if bypass cap is plus side 'toward' V+, and negative at Gnd.
  You said breadbaord...first, try to bias a Pi transistor without the extra clipping components, just the resistors [see last stage].
  The cap to diodes from the collector blocks DC and allows the 470k to pull up base bias.
  You noted all three leads of transistor read the same: check for non-continuity between the transistor leads.
 

[Radamus]

I've soldered the board so making it look exactly like the schematic would be kind of difficult. The only problem I can think of in not having precisely like the schematic is if for some reason the wires need to connect to a single point before they connect to another piece. I understand that making it just like the schematic would help me see how everything connects, but I'm not sure I can do that without making my mess worse now. I can post some pictures if you would like.

I'm not sure what you mean by Non-connections. Things that don't connect? I can double check for solder bridges and mistakes.

As for the resistance, I can certainly check all of that, but what am I looking for? I'll post that data as soon as I can.
I can also post the voltage at each of the transistor leads of all the transistors if that would help, but isn't voltage supposed to be constant where it isn't used (voltage drop)? So voltage should be around 8.34 everywhere? I thought resistors resisted current, not voltage.

Okay, well I'll take all of that advice and try to get back here soon. I don't feel comfortable starting a new pedal until I've figured out what's wrong with this one.