Silicon axis face not working [re-done, working, thanks!]

[Herr Masel]

About a month ago I breadboarded this circuit (from fuzz-central) but took it apart firstly because it gave really low volume and I couldn't figure out why, and secondly because I wanted a more nasty sounding fuzz (which I have yet to build....... for all kinds of reasons). So last night I decided to give it another go, my band is playing a show tomorrow and I've taken my big-daddy distortion apart so I really want to get this to work fast.

My biggest problem is that it doesn't work at all, no volume no nothing, even though I've went over it more than twice and I am PRETTY - I learned to be reluctant with using the word "absolutely"! - sure that it is wired up correctly. I also can't get it to bias right, whether using a 10k, 50k or 250k trimpot when maxxed the collector of Q2 reads 3.8 or so. Here are the readings from the transistors:

Q1-2n2369a
Gain: 97
E: 0
B: 0.67
C: 8.96

Q2-BC107b (I compared the datasheet to the recommended BC108 and they seem very similar)
Gain: 154
E: 0
B: 0
C: 9.24

The battery measures 9.28 whether connected or disconnected from the circuit.

At first I had lug three of the gain pot wired incorrectly to q2's collector, then the reading on q2 were e:0.01 b:0.01 and c: 3.88. Either way I cannot get the circuit to work or bias to 4.5v, I've tried a 10k trimpot, 50k, 250k....
Thanks.

[petemoore]

Q1-2n2369a
Gain: 97
E: 0   {OK connected to ground = 0v}
B: 0.67 {Not too bad but...
C: 8.96  {This ones very near V+ Voltage wise, I'd take another look here at counting node connections on schem and board.

Q2-BC107b (I compared the datasheet to the recommended BC108 and they seem very similar)
Gain: 154
E: 0  {Should have something near but not ground voltage
B: 0  {This is to be connected to Q1 Collector so voltage potential at both whould be =
C: 9.24 {Will probably change when base is biased
   Everybody note, without supply voltage measurement these shown #'s have no exact reference. I figure it's got to be at least 9.24vdc...or more.

[Herr Masel]

Fixed.

[petemoore]

  Cool !!

[Herr Masel]

  Cool !!

Oops. I just realized this. I meant I fixed the original post to mention the battery voltage, unfortunately still no fuzz!!

[guitar_199]

Track down why you have 8.96v at Q1-Collector and 0v at Q2-Base.

I am looking at the schematic and Q1-C goes straight to Q2-B and a 100pf cap goes from Q2-B to Q2-C.

That means that from one end of a copper trace to the otheryou are losing the base bias to Q2.  I think as soon as you find that, you will find that Q2 will turn on, Q2-c will come down to something more reasonable and the resulting bias of Q2 will cause Q2-E to go up which will wrap back to Q1-B and bias it on some.

Good luck
Bob

PS    Did you make/buy  pc board or are you using a vero board layout?

[Herr Masel]

Thanks guitar guy, but it is still on the breadboard so -
*bad traces/pcb are ruled out
*Q1-c, Q2-b and one lead of the 100pf cap are connected on the same strip so  that can't be wrong either.

The only thing I can think of is asking whether the order of the connections on the breadboard is important. For instance the row for the connections of Q2-c looks like this:

Q2-c
Jumper wire to lug 1 of trimpot
-
-
lead of 100pf cap

I've never given this any thought. Could it be the trimpot is stealing all the current before it gets to the capacitor, meaning I should reverse their order? I always figure that since all these spots connect to eachother when I solder them it doesn't matter what order they are on on the breadboard.

EDIT: Never mind, I tried changing the order it made no difference with the voltage readings.

[Herr Masel]

Damn, things are so crowded on the breadboard I noticed I forgot to connect the 33k resistor and Q1-c with the 100pf cap and Q2-b. Sorry, the readings are now thus:

Q1
E: 0
B: 0.67
C: 0.67

Q2
E: 0.08
B: 0.67
C: 8.18

Despite that, there is still no sound and I still can't get it to bias properly. I do believe there are no more mistakes but I will keep going over it looking for basic stuff. In the mean-time, any other ideas?

[johngreene]

The emitter of Q2 should be connected the the base of Q1 through the 100K, so their DC voltages should be very close. But definitely the base of Q1 should not be higher than the emitter of Q2.

--john

[guitar_199]

Good deal!  Now we are getting somewhere!
If you have the trimpot in place..... you should be able to adjust it  and set Q2-Collector to half of the battery voltage.  I mean.... if the battery measures 9.5vdc   then set Q2-C for about 4.75vdc.

This should be passing sound at this point though.... so also go back and check:

1) the inputs  ( the jack/guitar input should go to one end of the first pot and the wiper should go to .22uF capacitor which should then go to Q1-Base ) THe input jack should be grounded.

2) the outputs ( between the two resistors in the Q2 Collector circuit should be attached one end of the .01 uF cap.  The other end of it should go to the top of the volume pot.  The wiper of the volume pot should to to the output jack/amplifier.   Both the output jack and the volume pot should be grounded.

Make double sure that those connections are right...

[petemoore]

Q1
E: 0
B: 0.67 [Looks like this SHOudn't be connected but is, to Q1C]
C: 0.67 Looks like this is connected to Q2B

Q2
E: 0.08
B: 0.67
C: 8.18
  Yupp, missed value, misconnect or too many...not enough
  I've heard breadboards can be 'funky', I don't have one, but I do go through and DMM...everything, resistor values, actual connects etc. ...after determining via DMM that Q1C/B are not connected.
  Jacks and switches, well I sort those separately, TEHO, but again the DMM will tell what's actually going to exactly where and no more/no less.

[guitar_199]

Whoa.......  I just now saw what you were talking about.....and I missed it when I looked at Johns post.....


Q2-E being 0.08v yet.... Q1-B being 0.67.....   something is rotten here.

That's when I pull everything out....  have a "hand-steadying drink"...... and set it up again.


I wonder if the tranny's are in correctly?

[petemoore]

  12 parts...should be easy...not neccesarily
  Count part connections at each of the nodes, one by one, mimic node counts on schem to board
  Measure every resistor
  Get the data sheet for the actives, recheck pinouts, most NPN FF Q's flat side faces output.
  polarities looked at, one by one [diodes, caps, PS]
  jacks and switches should be looked at closely [I simply overlook/eliminate them entirely, focusing on the circuit alone, in the test jig I know, and/or can test if it works for in/out/Gnd.] In this case though, bias is issue enough for the time being.
 
 
 

[Herr Masel]

Thanks everyone, I didn't have any time since yesterday as I had a rehearsal and then it became two o'clock in the morning. Now I just woke up and need to get going, so it looks like I will be playing this gig without the fuzz face. I definately want to finish it so I will look at the stuff you advised tonight (if not tomorrow) and write back.

[guitar_199]

Also, I don't know if you have the ability to do this........but
do you have a digital camera such that you could take as close a pic as possible of the circuit
as breadboarded......  another pair of eyes might help.....

Bob

[Herr Masel]

Ok I'm back. First of all I managed to get the Q2-c voltage to 4.5, the 10k trimpot couldn't do it, I had to use 100k. There is still absolutely no sound coming from the effect. I fiddled with the my audio tester a little and there were a few places where I got a semi clean signal at really low volume, and one place where I got a kind of distorted signal at a little more volume (still quite low, and not the distortion it should be giving), that place is right at the input, where the tip of the jack and lug one of the smooth pot meet. Like I said, this is the closest I got to the fuzz, everywhere mostly didn't work at all. This is my first time using the audio tester (thank you Paul), but from my understanding the circuit should STOP working at the trouble spot, in my case - EVERYWHERE?

Another thing I should note is that when I play with the audio tester in that spot the volume pot doesn't respond, and the smooth pot acts as a volume pot (I can't tell if it also changes the character of the fuzz, if you can call it that). Do   you have any ideas what could be the problem? I rechecked the voltages, they haven't changed, other than Q2-c which is now biased properly. If there is nothing else you can tell me I will just pull it all out and start again though I don't know if that will help... it's strange how such a simple circuit can be so difficult....

[Herr Masel]

I took the fuzz apart and redid the entire breadboard layout. I measured the resistors, checked the pinouts, polarities, checked the wires from pots and switches were soldered properly (using the continuity mode on the DMM). I remembered to connect the battery cables and open the guitar's volume (stupid but this has held me back a little in the past). As my friends can testify, I don't often lose my patience or get angry but a sense of frustration is creeping in, during most of the week I didn't have time and now it's the weekend and the thing I waited so much for doesn't work. I feel like I am no good at this right now. Like I can't back up my enthusiasm with results. What the hell can I do that I have not done to make this work?

[petemoore]

  I find audio probing more useful with multiple amplifier stages, to identify the one that isn't. The FF being an amp stage, audio probing is less helpful to me.
  I dont use BBoard, perhaps there's a problem with that.
  I just use the DMM every which way I can think of.
  IF theres a small resistor to ground, it'll probably measure a voltage near gnd. or slightly above 0v.
  ROG has posted FF pin voltages, using them as a reference, or something to try to get sort of close to may help.
  One missed connect or resistor misvalue will disrupt maybe all the pin voltages, application of the DMM in Resistance and Voltage and continuuity mode will tend to find any.
  Continuity...check for connections/misconnections [where they 'arent' or where they shouldn't be too] all must 'be' any that arent' shown on the schematic can't 'be'.
  Resistance...just check resistor values.
  Voltages...'might' show you which pin to look 'around'...for resistor misvalue/misconnect/nonconnect...
  Q2 should bias with a collector resistor between say 5k-20k. Both transistors, all pins must be within the bias for operation...base at least .6v above the emitter, collector higher than base, Q2C at about 1/2 of supply Voltage.
  just figure you're getting a good dose of degubbing experience...

[johngreene]

Ok I'm back. First of all I managed to get the Q2-c voltage to 4.5, the 10k trimpot couldn't do it, I had to use 100k.

Don't get too frustrated. If you had to go up to a 100K pot, there is a distinct possibility that the transistor is in backwards and you are biasing it on the leakage alone. With a 100K pot full on, you are looking at less than 90 microamps of collector current. Can't be right.

--john

[Herr Masel]

Ok, I changed the volume pot because I thought it was bad and fixed a few more mistakes, I got the Q2 collector to bias right with the 10k trimpot and all the other pinouts are really close to the recommended one's on ROG. My ruby kicked the bucket it seems, which was misleading me because I was looking at the fuzz for problems, the ruby now does a really cool controlled motorboat with ringmod sound.

On the axis face, the volume is very low and the pot doesn't respond but I can tell I wired the pot badly (some wire cutting off and I melted some of the rubber shileding which probably flowed onto the lead). I am pretty sure it is the pot because when I touch the connections with my thumb the volume goes way up, I will fix it tomorrow, I want to get some reading done before I go to sleep. In the meantime, the fuzz is REALLY harsh, not like the last time I breadboarded it (and took it apart) but I used different transistors, though gains of 97 for Q1 and 156 for Q2 isn't too high is it? Should I use lower gain ones? There is also very little bass response but I need to redo the volume pot before changing anything, the nasty sound may be due to it.

Thanks a million guys for pulling me through, I hate to think I'm already too good to make the small mistakes and have 'mother nature' (I'd say Eris) slap me in the face. I deserve it  . Hopefully the volume pot will fix everything, I will let you know tomorrow.