Axis Face Debug - HELP!

[enigmur]

Heh sure you all saw this comming, I started a new topic because my old one was getting farther away from the origional topic.

http://www.indyguitarist.com/torchy/Distortion_Overdrive/Axis%20Face%20-%20Si/Axis_Si.gif

I finished the circuit today. All parts are correct. Polarities of elec caps are correct.
I dont get any sound out from the circuit at all.
Trimpots are 503 (50K) and 103 (10K) and are placed correctly

To be honest Im not totally sure it is wired up properly. I do not have a switch and it is wired like this -
+9V into the board
-9V onto the input jack Ring

Input tip to input on board
Input sleeve to circuit ground

Output sleeve to circuit ground
Output tip to 100K pot 3rd lug

The pots are all wired up 1-2-3 with the shaft facing up and the lugs toward me.

100K Volume pot - Output on the board (R9 in diagram) goes to lug 3, lug 2 goes to output tip. Now does lug 1 have to go to ground or is it left free?
1K Fuzz Pot, 5K Bias pot - both wired as the diagram indicates.



The first battery I used read around 4V, but tried the one out of my wah and it was over 8V - both with no success.

I tested the transistors in my DMM and found they are BCE and read about 120hFE, so have crossed the C and B legs around on the circuit (so they are CBE as the circuit  needs, the legs dont touch).
With my DMM on 20V the legs read -

Q1
C - 0.01
B - 0.43
E - 0.00

Q2
C - 0.01
B - 0.01
E - 0.00

Now I think the volume knob works, because if i hold it and turn it, it will turn the buzzing down and off.

What are some tests I can do with my multimeter to find the problem?

[enigmur]

I have a few more things to add, after reading more of the debug thread.

With the negative probe on the output jack ground, and the positive probe where the battery positive meets the board - it is 6.25V
My negative battery lead goes to the input jack, so I'm not sure what to test here... If I test the black wire on the jack it is 0V

Okay, new transistor readings... I have no idea but they are different this time Im trying (maybe because i dont have an output plugged in?)
Taken with DMM set on 20V, negative probe on the ground wire on the output jack.

Q1
C 0.65v
B 0.57v
E 0.0

Q2
C 0.10
B 0.10
E 0.00

As I was doing the 2nd transistor, i went back and checked C at Q1 and for some reason it was reading 0.10V, instead of the 0.65V i got just before...

I will try again now.

Yupo it has stayed out this time... God this is confusing!! I am having a bit of fun learning to use the DMM, its cool to find resistance on pots.

Interesting... I turned the trim pots fully counter clockwise and did a reading again

Q1
C 3.75v - slowly creeping up. Started at approx 2.55V
B 0.60v - staying put
E 0.0V - staying put

Q2
C 3.75V - slowly creeping up. Started at approx 2.55V
B 3.75V - slowly creeping up. Started at approx 2.55V
E 3.15V - slowly creeping up Started approx 2V

Some of these seemed to keep slowly creeping up as I took the readings.
After about 10 mins from when I turned the trimpot, these readings are what I would consider to be final, though they raised slightly over then dropped.

So theres a bit more investigation from me, hope that can give some clues!

[petemoore]

Heh sure you all saw this comming, I started a new topic because my old one was getting farther away from the origional topic.
  Not really, this debug page looks pretty complete, well drawn.
http://www.indyguitarist.com/torchy/Distortion_Overdrive/Axis%20Face%20-%20Si/Axis_Si.gif
I finished the circuit today. All parts are correct. Polarities of elec caps are correct.
I dont get any sound out from the circuit at all.
Trimpots are 503 (50K) and 103 (10K) and are placed correctly
To be honest Im not totally sure it is wired up properly. I do not have a switch and it is wired like this -
+9V into the board 
-9V onto the input jack Ring
  Input tip to input on board
Input sleeve to circuit ground

Output sleeve to circuit ground
Output tip to 100K pot 3rd lug

The pots are all wired up 1-2-3 with the shaft facing up and the lugs toward me.

100K Volume pot - Output on the board (R9 in diagram) goes to lug 3, lug 2 goes to output tip. Now does lug 1 have to go to ground or is it left free?
  ..either way..it'll output, a 3lug VC wiring assignment forms a voltage divider between signal path and ground, 2 lug VC wiring puts the signal through the variable resistor...I guess they call 'padding it down', attenuating to some degree. the schematic shows one outside lug of VC pot to ground, the other outside wired to circuit output, wiper gets the variable resistors divider output. 'Turn the pot down and wire that lug to ground', or wire with wiper to output and reverse outside lug assignments if CW turns it down.
*1K Fuzz Pot, 5K Bias pot - both wired as the diagram indicates.
  The first battery I used read around 4V, but tried the one out of my wah and it was over 8V - both with no success.
  4v is too low, around 7v or more is better.
  I tested the transistors in my DMM and found they are BCE and read about 120hFE, so have crossed the C and B legs around on the circuit (so they are CBE as the circuit  needs, the legs dont touch).
  But what transistors?, common pinout is EBC, does the meter have an HFe tester, this can verify pinout.
    With my DMM on 20V the legs read -
Q1
C - 0.01
B - 0.43
E - 0.00

Q2
C - 0.01
B - 0.01
E - 0.00
  the battery may not actually be connected or is shorted, test between poles for 'no short', then from each pole to the board assignments, red is +.
  Now I think the volume knob works, because if i hold it and turn it, it will turn the buzzing down and off.
  clip a lead to ground, test all ground points marked.
What are some tests I can do with my multimeter to find the problem?

Test battery poles for no shorts.
  Clip DMM to the battery wires pole+ button, test to circuit point connection [BM=beep mode].
  Clip DMM to ground, test all marked ground points on schematic.
  Do node counts, write node 1, it gets the source [and pulldown resistor]..clip lead on Gnd. measure resistance to node 1 [should be less than/about 1 meg if that's what the pulldown is], and then clip to input tip..should beep to node 1, while there test that ground is not on the node.
  Continue with each node individually, count the # of connections at a node as marked, then test on the board to verify them, noting 'special' considerations like transistor pin ID and capacitor polarity.
  The line on the SI protection diode points up.
  Something is not powering most likely...for all readings to be in the <.5 zone, that and the buzzing/buzzoff/touch comments is a possible ground lifted...which of course throws everything off like that.
  You should measure about 1k across the gain pot, 10k across R6 etc., 100k between Q2E and Q1B...

[enigmur]

Thanks a lot! I'll try the suggestions I understand out 

Just noticed something, the 10nf cap at C4 is about 3V on one side and nothing on the other side. The side reading nothing is inline with the output. I cant get a reading from the output wire on the output jack, on the volume pot, or anywhere - could it be a bad cap? The cap is 103K, so it is 10nf. Ill try another one in there though and see if it makes a difference...

[enigmur]

I replaced that cap with a 103J, and the contact looked dodgey so I redid that too.

Now I am getting sound thru the circuit!

The bias pot does nothing, but when turned all the way down it turns the sound off, and gives a slight rustle at the emd.

THe fuzz pot turns the sound down and off quickly, but has a loud rustly kinda sound when it does

And the volume pot does really do anything I can hear, but doesnt make a sound when turning it down.

The pots are wired with the shaft facing down and lugs toward me, 1-2-3 as per the diagram

I tried turning the bias trimpots and R2 trimpot turns down the volume when turned clockwise, and the R6 trimpot turns down the volume almost instantly when turned clockwise at all, it also has a rustling sound.


On the 2nd pot (fuzz) it says one contact gets wired to lugs 2 and 3, I have wired the wire to 3, and bridged the two lugs with wire. Is that okay?

I would have thought volume would have to be grounded?

I am happy that there is at least sound coming thru it now, I know it is a circuit at least. I have a feeling that something just isnt wired properly, or something obvious...

Please give me some ideas! I had a dream last night that i got it working (i know, geek...)

Cheers!

[enigmur]

Okay more voltage testing.

Over the bias and fuzz pots, when turned I get increases and decreases in voltage, which would point to these working.

I can't pick up a voltage on the output tip, the output or input on the board, or the capacitor at C4 (the leg going to output). Should I be getting voltage here? I feel like I am close to fixing this bugger - So if anyone can please look over these readings it would really help me out.

I can post a couple of photos of the board if that would help

[petemoore]

I can't pick up a voltage on the output tip, the output or input on the board, or the capacitor at C4 (the leg going to output). Should I be getting voltage here?
  Capacitors block DC voltage,The rest of the [up and down' part] circuit goes to ground or V+.., the 'right and left' wires [input, output, have DC blocking caps, anything connected 'outside' those is outside the DC circuit or 0V.
  Voltage on the transistor pins is what tells the bias.

[enigmur]

Thanks Pete, thats one less thing to worry about.

Any ideas where I should be looking since I have a full circuit but the knobs dont do what they should and I don't get fuzz? I've posted everything I could think of but Im just waiting for some godly person to come along and point out what my problem could be.

The fact the pots and trimpots are making sounds makes me think possibly something isnt wired correctly

[enigmur]

I just plugged it in and where I thought turning the pots up was getting rid of the sound, it is actually making it fuzz.

I have to play really hard and it makes a quiet farty fuzz which cuts in and out really easily. Its like it is only picking up the really high input from my guitar, when I play the low E really hard.

I tried some other transistors in (much higher hFE) and I found the same thing.

So for some reason it is like the transistors arent getting enough power or putting out enough power...

[petemoore]

  Voltage measurements tell part of the story, if the part they tell isn't consistant with operational standards, something is causing the voltage measurements to be 'off' from where they should be.
  Misconnections.
  One too many connections.
  Misvalued resistor.
  these are the three most likely candidates, the DMM can be applied to test every one of them, 'godlike' is a matter which often has to do with some luck...it is always one [or more] of three or ten things that can go wrong, which did go wrong...if the first thing checked is the only problem, the debugger is happy, [especially if that was the only thing], if it's the 15th thing which reveals the problem [and leads directly to a solution] it is still good debugging.
  Often it is the dogma which helps out, dogmatically applying the DMM [circuti powered and non powered], testing using the various methods listed with the DMM manual...every which way you can apply the DMM...but take notes and theorize as you go, sometimes you can think through to the 'most likely to bring info' application technique of the DMM and save time.
  Are you still getting 'near Gnd.' voltages on the transistor pins?

[enigmur]

Hi pete.
No the voltages I get on the transistor pins changes with the bias trimpot moved, I was getting really low voltages, then changed the trimpot and it gets up to around 4.2V I believe. The odd thing to me is that both the trimpot and the bias pot make the same harsh rustle when moved to a certain end - lug one is on the same connection as C of the transistor, and 2 and 3 lugs of the pot are on the same connection as a leg on the trimpot.

I know it must be close because it is actually working, but there must be one thing not quite right which is stopping the circuit from outputting.

I will try change a couple of resistors after work today - I have checked over all parts a number of times and they all seem right.

If all else fails I will re-do the board.

[enigmur]

Ive been reading problems on fuzz face circuits and found a couple sounding the same as my problem. They get a quick farty fuzz when strummed really hard.
When I turn down fuzz and bias my guitar tone comes thru clean.

I saw someone suggest it could be Bias of the transistors. What voltages should I be aiming for? I feel as though there must be something else wrong, or could it just be the bias set wrong?

This is still basically my voltages

Q1
C 3.75v Can raise about 1V with bias
B 0.60v Stays the same
E 0.0V Ground

Q2
C 3.75V Can raise about 1V with bias
B 3.75V Can raise about 1V with bias
E 3.15V Can raise about 1V with bias

Are these out of the ordinary?

[tcobretti]

I would look for solder bridges between the C and B of Q2.  I guess it could be a bad transistor also, but your symptoms are classic mis-bias symptoms, which could be related to the fact that the voltages look wrong for Q2.

[enigmur]

Ok thanks, maybe the legs are touching since the transistor is BCE I had to cross two legs. I have like another 4 of these trannies so if need be ill try some other ones - but I did try a different higher gain transistor in there and it basically had the same problem - which definately didnt have crossed legs.

I think I am going to just totally re-board the thing when I get home, and really make sure to do everything as clean as possible.

I just can't see any solder bridges or anything on it, but there MUST be something along those lines in there causing the problem, so a clean start would possibly sort it.
It could be Bias, but that rustling that the bias pot and one of the trimpots make suggests to me that something else isnt quite right (not that I know what I'm doing - instinctal guess haha). It is just odd that both the pot and trimpot make the same noise, in the same approximate range of turning the pot.

I've tried changing the trimpots and pot everywhere but just cant get it to put out a higher level when fuzzing. I think there is some kinda problem around that Q2 transistor and the trimpot and pot controlling it.

[enigmur]

I re-did a strip board and its working this time!

Couple of problems.

1. Volume pot barely does anything, seems to turn the treble up more than volume.

2. Fuzz pot only controls fuzz in like the last tiny turn, before that it just turns it muddy sounding.

3. The bias pot is fine when turned totally one way. When turned anti clockwise (to lower the collector voltage on Q2) it slowly introduces this peircing whistle. If I touch the first lug on the pot it does the same horrible whistle. What could this be?

When biasing the Q2 transistor, do I have the bias pot turned up or down?
What should I bias the Q1 transistor to?

My voltages are  -

Q1
C - 1.36
B - 0.54
E - 0.00

Q2
C - 4.45V (Bias pot turned down) 8.91V (bias pot turned up)
B - 1.59V (Bias pot turned down) 1.35 (Bias pot turned up)
E - 0.78 Stays the same

I am definately closer this time, the fuzz sounds awesome and will be amazing when I can totally control it - I cant at the moment due to the controls acting funny.
I bought a fresh battery today too.

Here is a diagram of my wiring

What could that whistling/squealing be and does my bias look okay?
Please help me finish this bastard!!

[tcobretti]

Congrats!  It took me a while to get used to working on vero and I had lots of problems like you are talking about, in fact I recently built a phaser that I finally had to give up on.

On the volume pot, Lug 1 goes to ground.

I feel certain that the Fuzz pot, and possibly the bias pot are miswired, so check those carefully.  That squealing is likely oscillation which is like feedback inside the pedal itself, usually caused by too much gain or from using long, unshielded wires.  The traditional fix for it in a Si FF is a small cap (50pf) across the base and collector of the transistors.  However, this circuit is designed not to need that cap if you use the specified transistors.  I read that yours are 120hfe, and that's pretty low, so once again I suspect that problem is wiring.

[enigmur]

Thanks for that! I thought that there should be a wire going to ground off the volume pot - isnt that how it works? When you turn the knob down to directs more current to ground instead of the output?
The wires arent too long, most are approx 2 inches I guess.
How would you wire the pot which has one wire going to two lugs? Also the smallest cap I have is 100pf, so I'll try that tomorrow anyway. There definitely arent any solder bridges this time, all the breaks in the vero strips are drilled so are totally cut off, and after reading a bit lesson on soldering - I feel the soldering is a hell of a lot better this time around too.
I can't see how it would be wired wrong, unless there is a different way of bridging those two lugs on the bias pot. Should I try that cap on the transistor? Also I have a transistor which reads about 160Hfe, could I try this in Q1 or Q2?
Any ideas why the fuzz pot isnt doing it's job smoothly?

[tcobretti]

I thought that there should be a wire going to ground off the volume pot - isnt that how it works?

Yes.

How would you wire the pot which has one wire going to two lugs?

I personally just wire those types of pots with one wire to the wiper (Lug 2) and the other to one of the other Lugs.  The only difference is it changes the direction of travel.  Running a wire to two lugs is unnecessary, but very common.

I don't think the cap on the transistor is going to solve your problem, but I guess you could try.  I would take out the 5k Bias pot and install a jumper where that  pot connected just to simplify things; you can always put it back later.  If that solves your problem, then you know what the culprit was.  If it doesn't, you know the culprit is likely the fuzz pot.  Then you have to figure out what is wrong.  I'd measure the pots from lug 1 to lug 3 with a multimeter to be sure they are measuring the ohmage they are supposed to.

At this point, you may just have to tinker til you figure it out.  You could also try posting clear detailed pics on the offhand chance we can spot the problem.

[enigmur]

Thanks a lot for your help, just having ideas to try means im not totally cornered.

I'll hook a ground to the volume pot, and see what that does.
Then I ll try removing the bias pot.

Then Ill work from there

Alright, I'm still getting the problem, I have taken out the bias pot and jumpered it. I have tried a different cap to ground. Ive swapped out the fuzz pot for a different pot. Ive tried a different transistor.

The fuzz control still doesnt seem to work properly, and when I turn the voltage down on the bias trimpot it still squeals.

What could cause feedback inside the circuit?

[enigmur]

I think Ive traced it down to the fuzz control. When you turn it up full, it provokes the squealing. now on that pot, one goes straight to ground, one to ground thru a capacitor and the other goes to the emitter of the transistor.

I am totaly lost for ideas, I dont know what the voltages should be. Everything is doing its job. Ive tried 2 totally different elect caps, transistors.

Please does anyone know what the hell this could be?