Fuzz face - strange things afoot

[Chris oej]

Hello all

I have a fuzz face build that has a very strange effect n
I've built a fuzz face with bc183l's. The pedal sounded great until I put it all in the box. Now it seems to sound as if there is a very heavy noise gate one the pedal - when I play a note I get the sound of the fuzz but then a shorly and sharply cut off the note.

I've gone over the circuit again and again, even built a new circuit board incase one of the components had gone faulty but still the same thing. I've insulated the inside on the box incase something wasnshorting via the box itself. All the components are exactly as they should be and it appears to all be wired in correctly. The bypass works fine.

Has anyone else had this problem? Does anyone know what can be causing this strange effect.

Any help would be appreciated so so much

Thank you

[petey twofinger]

i had this once with an oscilator circuit . it drove me nuts . 

what it was was this , the screw holes on the pcb did not line up with the stand-offs , so when i tightened it up , the board flexed a little which did SOMETHING to make it work for a second , the pitch would rise and it would fail . i slowly and carefully drilled the holes at the proper angle to make them line up . it worked .

what i would suggest is try removing just the board , and see what happends . then take a pot off , etc . you will find , by process of elimination , you can narrow it down , then maybe use a magniying glass , run a pick around all the traces , reheat all the solders . look for anything that is too close , cold jointsa , bad connections .

i did have another scenario exactly like this that was different , and that was related to grounding . if THAT is the issue , you may figure that out by the same process . somethings are getting connected , electricly , when its in the chassis . so you would need to isolate something from the chassis , use a diode , or something . goodf luck , and if you figure it out , why not post up what it was , thanks . (most folks dont, i hate that !) . oh and good luck .

[LucifersTrip]

what were the voltages on the transistors before & after you boxed it?

what you described sounds like standard misbiasing.

if you did not accidentally short or disconnect something as petey twofinger suggests, try adjusting Q2's collector resistor to get the classic 4.5v on Q2's collector.

[Chris oej]

I've taken it out of the box and it not working out of the box now. I'm assuming I must have messed a conection  somewhere but can't work out where. The readings from the transistors are below. I wasn't sure if you're meant to measure them with one of the probes on the + or - so I've measured both

Probe on +
Q1
E 7.9
B 7.24
C 6.71

Q2
E 6.65
B 6.7
7.8


Probe on -

Q1
E 0
B 0.6
C 1.19

Q2
0.72
1.19
7.72

As you can see there's no 4.5. Where do you think it could be going wrong?

Thanks guys

[zombiwoof]

This may be a dumb question, since you say it did work at some point, but did you get the pinout correct on those transistors?.  I know that BC183L's have a different pinout than the common BC108/109 etc. and the leads have to be crossed to fit the normal sockets for the other transistors.  Even if you know this, make sure that the leads of the trannies are not touching each other where they are twisted to fit the sockets.

Just something I thought of because you mentioned you used BC183L's.

Al

[R.G.]

Any time something works outside the box and then quits when you put it in the box, the process of mounting it in the box is doing something.

This can be shorting to the box, flexing the board and opening a crack, flexing a cold solder joint, shorting an incorrectly wired jack, even causing RF oscillation by bring the right (or wrong!) leads near each other. It's highly specific to the box and layout. So every case is different.

[LucifersTrip]

I've taken it out of the box and it not working out of the box now.

not working? no fuzz or no sound at all? 

I'm assuming I must have messed a conection  somewhere but can't work out where. The readings from the transistors are below. I wasn't sure if you're meant to measure them with one of the probes on the + or - so I've measured both

Q1
E 0
B 0.6
C 1.19

Q2
0.72
1.19
7.72

since you are using BC183L's which is NPN, it is negative ground. black lead on -, red lead on the point you are measuring.

As you can see there's no 4.5. Where do you think it could be going wrong? 

exactly what I suggested a few posts earlier:
http://www.diystompboxes.com/smfforum/index.php?topic=94094.msg810881#msg810881

I wrote "if you did not accidentally short or disconnect something". As R.G. suggests, that is probably the case.

I would start by measuring Q2's collector voltage (what you reported as 7.72) and jiggle and flex the board and components gently to see if the voltage changes.   Since it worked at one point, you are trying to find the bad/shorted joint that was caused by boxing.  Also, use the meter to check continuity between joints.

A lesser chance is that you've blow a component and need to replace something.

[alfafalfa]

The same happened to me when I put a perfectly working CE-2 chorus clone into its box . It stopped working .

No matter what I tried I can't get it working again.  It's must be a faulty connection I gather. Or I did something stupid. It's very frustrating.

This is a more complex project than a fuzzface so i'm going to build it again  on a somewhat bigger board.

My advice to you is :build it again because the your project has so few components. It won't take much time and less than finding out what's wrong with the disfunctioning one.

[Chris oej]

Hi all

I've tried rebuilding the entire board from all new components. I've tried shorting out the pots and 3pdt switch.  And still the same problem - short sharp bursts of fuzz, as if it was being played through an extreme noise gate.

I've noticed that on fuzz central's schematic for the silicon fuzz face the polarity of c1 (the 2.2uf capacitor at the input) is the oppersite way round to the schematic of a silicon fuzz face on Beavis audio. I've tried my board with c1 both ways round and yet I still have the same sound. This strikes me as odd - surly if it is the wrong way round there would be no signal at all.

I definatly have the transistors in right. bc183l's have a bce pinout and I checked them on the multimeter before installing them.

I had a wobbly conection on point 3 of the fuzz pot so have resoldered.

I'm really puzzled by this.

Thanks for all your suggestions, I'm trying them as you post. I'm determined to get this pedal working!

[LucifersTrip]

Hi all

I've tried rebuilding the entire board from all new components. I've tried shorting out the pots and 3pdt switch.  And still the same problem - short sharp bursts of fuzz, as if it was being played through an extreme noise gate.

with 4.5v on Q2's collector?

I've noticed that on fuzz central's schematic for the silicon fuzz face the polarity of c1 (the 2.2uf capacitor at the input) is the oppersite way round to the schematic of a silicon fuzz face on Beavis audio. I've tried my board with c1 both ways round and yet I still have the same sound. This strikes me as odd - surly if it is the wrong way round there would be no signal at all.

this is correct for bc183l's:

I'm really puzzled by this.

Thanks for all your suggestions, I'm trying them as you post. I'm determined to get this pedal working!

if it doesn't work with 4.5v on Q2's collector or you can't get 4.5v, post a clear closeup pic of both sides of the board and someone may spot the error.

[Chris oej]

Hi all,

I've tried adding a 43k resistor in place of the 8K2 and have achieved 4.8v at Q2 collector. However, it's still having the same problem. I read this:

http://www.geofex.com/fxdebug/bias_prob.htm

Is it possible that the problem is with the capacitors? Or that i'm using the wrong kind of resistors - ones which aren't effective at 9v?

Here are the pics of the board with the 8k2 in place:

http://s728.photobucket.com/albums/ww286/chris-oej/fuzz%20face/

I've checked for shorts and there are none - also, i checked all the resistors and they are all resisting the correct amount.

Thank you guys for your time helping me.

[Davelectro]

43K on Q2's collector?

That's way too high. Pinout must be wrong: for BC183L the middle leg is collector, not base.

[PRR]

Or the 1K pot is wrong or not-connected.

[Chris oej]

It works... Well almost.

I replaced the 1k pot and put the 8k2 resistor back where it should be and it worked (thanks develectro)! So I put it in the box and it still worked... Then it went dead. Now I get no sound at all. I've tried wiggling the wires and still nothing. I'm assuming I must have a bad connection somewhere.

Does everyone have this many problems making their first pedal?

[petemoore]

  I did...and the second...
   So the collector doens't wanna get 'low'...[compared to supply voltage...what that is might matter.
    Anyway look around 'below' at the gain structure/emitter area, count the node connections and veryfy that only those and all those are made.

[Chris oej]

It works!!!!! I've also added a 0.8nf capacitor over the base and collector of Q1 to eliminate the high pitched hiss and added another one over Q2 which can be tuned on and off via a DPDT switch - gives it a nice tone cut similar to a wicker switch on a big muff pi.

Thank you all so so much for all your help and suggestion, really appreciate it.

Thanks guys

[LucifersTrip]

It works!!!!! I've also added a 0.8nf capacitor over the base and collector of Q1 to eliminate the high pitched hiss and added another one over Q2 which can be tuned on and off via a DPDT switch - gives it a nice tone cut similar to a wicker switch on a big muff pi.

Thank you all so so much for all your help and suggestion, really appreciate it.

Thanks guys

That  sounds great!  So, what was the actual final problem that you fixed? Did you measure Q2 collector voltage now that it works?