Total Newbie question - debugging a Fuzz

Forum dedicated to helping people debug and troubleshoot non-functional pedals or builds. Please use an clear and informative title, indicating circuit and basic problem. Don't forget to mark the issue as fixed if this is the case.
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V8Reverb
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Post by V8Reverb »

I built the Fat Furry Freak fuzz pedal from pedalparts.co.uk and now I'm getting clean guitar (bass) with everything turned down but as soon as I move the volume it starts clicking only when I play a note. i checked the soldering and any bridges and the resistor values are correct and the electrolytics are in the correct way. What could be causing this?
I'm using Mylar greenies as capacitors - would they cause it? Would my transistor cause it if they were fried?

like I said - newbie quesion, sorry.

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Post by Lucifer »

It's that wire on the left - no, not that one . . . yeah, that's it.

Only kidding :lol: V8Reverb - but with a purpose. A picture is worth a thousand words. A bunch of pictures would be even better.

How about posting a few so we can have a look. There may be something obvious that we can spot.
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V8Reverb
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Post by V8Reverb »

lol the left one? Which way am I holding the board? :)

I'm in work at the moment so I'll get you some when I get home.
The only other thing I can think of is dry solder - the solder pads were the smallest I've ever seen, but I made sure it flowed and ended up with a ball on top so i'm not sure - i cut the legs halfway into the solder so something should have come loose if there was a dodgy connection

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V8Reverb
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Post by V8Reverb »

Image
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V8Reverb
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Post by V8Reverb »

oh and it acts differently with a power supply feeding it +9v
I'm going to resolder the wires for the pots and see what happens

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V8Reverb
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Post by V8Reverb »

After rewiring the pots it still clicked when I was putting a signal through it and then it stopped and all I got was clean bass even if I turned the controls all the way up. Guess I fried something.

Here's the pdf with the schematic if anyone wants to take a look
http://pedalparts.co.uk/wp-content/uplo ... yFreak.pdf

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LucifersTrip
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Post by LucifersTrip »

V8Reverb wrote:After rewiring the pots it still clicked when I was putting a signal through it and then it stopped and all I got was clean bass even if I turned the controls all the way up. Guess I fried something.

Here's the pdf with the schematic if anyone wants to take a look
http://pedalparts.co.uk/wp-content/uplo ... yFreak.pdf
Any good kit / pcb should come with a set of test voltages on the schematic or build instructions so you can troubleshoot.

I don't see anything on that pdf, unfortunately. I would email PPP.

That being said, it looks like a Fuzz Face variant with added features, so we can guess around what the voltages should be....and even if it wasn't a FF variant, we can still see by the voltages if the transistors are working properly.

So, for better help, please post Q1/Q2 e,b,c voltages

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V8Reverb
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Post by V8Reverb »

Q1 - c=1.808v b=102mv e=0v
Q2 - c=1.105v b=1.808v e=1.148v

does that 0v mean q1 is fubar?

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V8Reverb
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Post by V8Reverb »

Some voltages before the transistors:
C7 - 8.9 before and 0v after
R3 - 8.9 before and 1.8 after
R5 - 8.9 before and 1.19 after

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Post by LucifersTrip »

V8Reverb wrote:Q1 - c=1.808v b=102mv e=0v
Q2 - c=1.105v b=1.808v e=1.148v

does that 0v mean q1 is fubar?
no, look at the schematic....Q1E is grounded = 0

but, Q2 is not cool. E should be lowest, then B, and the collector should be the largest....and most likely, the collector will be in the 4-6V range.

Image


as a comparison, look at test voltages (thanx GGG) for a silicon Fuzz Face

Q1
Collector 1.4v
Base 0.6v
Emitter 0.0v
Q2
Collector 4.5v
Base 1.4v
Emitter 0.8v

Image

when your voltages are that far off, the first thing to do is make sure you have the correct pinouts and the correct value components....that's if you're sure the solder joints are good

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V8Reverb
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Post by V8Reverb »

Yeah sorry I forgot to post that I then realized that the 0v was ground.
I can't be sure that the solder joints are 100% - I did go over them all again, but the solder pads are tiny - I've got a replacement for the Q2 so I'll solder that in and see if things change - could it be R5 too?

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V8Reverb
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Post by V8Reverb »

Should there be that much drop across R5? It's a 20K

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Post by LucifersTrip »

V8Reverb wrote:Should there be that much drop across R5? It's a 20K
Q2C voltage is probably low but the bigger problem is that the base voltage > collector voltage, so the transistor is not functioning properly. are you sure you took correct measurements and you have the transistor in the correct way?

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V8Reverb
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Post by V8Reverb »

LucifersTrip wrote:
V8Reverb wrote:Should there be that much drop across R5? It's a 20K
Q2C voltage is probably low but the bigger problem is that the base voltage > collector voltage, so the transistor is not functioning properly. are you sure you took correct measurements and you have the transistor in the correct way?
Yes to both and I rechecked just now and got the same voltages. I'm going to replace it now and see if it changes anything

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Post by V8Reverb »

Didn't change - c=1.152 b=1.779 e=1.165

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Post by V8Reverb »

Ignore the 3.5 at the collector - it's actually 1.186 when i rechecked - not sure why it read 3.5 before - there's no signal coming out at all when I connect the amp and bass now...

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Post by LucifersTrip »

V8Reverb wrote:Ignore the 3.5 at the collector - it's actually 1.186 when i rechecked - not sure why it read 3.5 before - there's no signal coming out at all when I connect the amp and bass now...
it's not expected since Q2 is not working....maybe you read 3.5 before because of a bad connection. try reading the voltages again while jiggling the transistor and nearby components.

i'd start looking for solder bridges/bad joints and start testing continuity between components.

When troubleshooting, it's always best to eliminate everything but the circuit so wire straight thru with no switch.

...and definitely email PPP about voltages

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Post by V8Reverb »

I emailed ppp yesterday and he said "what a great idea! I'll get on to that as soon as possible" and had nothing since. I even asked on his Facebook page. On my way to work atm - I'll get to checking for bad solder joints when I get home later.
Thanks for your help so far

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Post by sinner »

I'm sorry to go off topic, but I'm so very happy it's not my fuzz again :mrgreen:



:whappen:

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Post by V8Reverb »

sinner wrote:I'm sorry to go off topic, but I'm so very happy it's not my fuzz again :mrgreen:



:whappen:
Is there any one issue that comes up a lot with your design?

I prodded each component, twisted the board, tried to move each one with a pen and the voltage still stayed at 1.186v

When I test before and after R5 - I get 9v before and 1.186 after - which is what the collector voltage is at Q2 - and across R3 its 9v before and 1.8 after which is what the base voltage is at Q2.

R3
Image

R5
Image

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