70's Silicon Fuzz Face

[mayburyds]

Hi,


I have a Silicon Fuzz Face that I bought in the 70's that I haven't used for ages but has developed a problem.


Using it with the volume up on the guitar all good but if I turn down the volume on the guitar I get random cracking/static/popping sounds through the amp. Stops when I turn the volume up on the guitar. Doesn't make difference if I back off the volume or fuzz on the pedal.


I have checked the hardware connections on the FF and re-flowed the solder on the board buy no joy.


Only happens with the FF.


Any ideas?


Many thanks in advance.


Cheers,


David.

[pompeiisneaks]

It's old enough that the electrolytic capacitors in it could be going out.  You could look here:

http://fuzzcentral.ssguitar.com/fuzzface.php

To see the schematic etc.  Otherwise, I'd guess it could be almost any of hte components going out.  I'd at least look at and test the electrolytics.

~Phil

[mayburyds]

Phil,


Thanks for the info and reply.


I'll get some new caps and swap them out and see if any make a difference.


Cheers,


David.

[mayburyds]

Hi,


Sorry for late update.


Swapped the caps one at a time and retested, still pops and crackles.
Did the same with the transistors, still pops and crackles.
New pots, still pops and crackles.
Bypassed the switch, still pops and crackles.
Jack sockets seem ok as when I wiggle the leads nothing changes plus it's fine when the pedal is off.
Haven't changed any resistors as they all measure OK.
Bias voltage on the second collector is 4v all other voltages seem ok.


Also, discovered it does make the noise when the guitar volume is turned up not just when the volume is down as I originally thought and if I plug in a Les Paul the pops and crackles are not as loud as when I have a strat plug in!


is it time to head for the trash bin?


Cheers.

[pompeiisneaks]

Get a chopstick and push on the resistors, some of those old carbon comps or carbon films (Not sure if these are). can end up making a lot of noise and may need replacing.

~Phil

[Ed_Chambley]

No trash bin!!!!!


I have the correct Germanium Transistors for a Fuzz Face. I know yours is Silicone, but it doesn't have to be. The original enclosure has value.  Why do you have full bypass?  It sounds like you are not getting proper pickup load. Does the crackle happen as the note begins to trail off or on the initial attack?


Do you have an oscilloscope? Usually it is the first transistor area and too resistors can measure good and still make noise.  If a scope, simply check the signal path.  when you clip on to the problem area you will see it.

[mayburyds]

Hi,


Thanks for the reply.


Sorry, when I said I bypassed the switch I meant I took the switch out of the circuit to eliminate it from the problem. It has the original DPDT switch. All the components are original apart from the pots and knobs.


I have been over the circuit with a simple audio probe and get a good signal across all the components.


The popping and crackling are there all the time regardless if the guitar is being played or not. It's louder with the volume of the guitar turned down and using a LP the crackling seems not as loud as with a strat. That seems to point to pickup load as you suggest.


I have put in new transistors which didn't make any difference but I haven't replaced any resistors as they all measure good. I change the resistors.


Cheers,


David.

[Ed_Chambley]

May as well try changing them, there are not many.

[mayburyds]

Hi,


Changed the resistors but no cigar!


The only component I haven't changed now is the .01uf cap.


Cheers,


David.

[pompeiisneaks]

Gah, well you changed all the most expensive stuff, might as well finish it up :)

~Phil

[mayburyds]

Hi,


Changed the cap made no difference 


Created MP3 of the noise it's making just in case someone has come across it before.


https://soundcloud.com/maybury1974/ff-1


Cheers,


David.

[mayburyds]

Hi,


At last some good news!


Did what Ed Chambley suggested and converted it to AC128's and now no more noise!


Can't explain what was going on with the silcon transistors as even the new ones I put in made no difference to the popping and crackling noise.


Only one small problem to fix and that is the 8v on the collector instead of the magic 4.5v.


Thanks to those who replied and to Ed for his suggestion.


Cheers,


David.

[mayburyds]

Hi,


Seems I'm not out of the woods yet!


Measured the Q2 collector voltage today and it read 4.5v! Keeping the DMM measuring the voltage and it started to creep slowly up.


Swapped the 8.2k resistor and the voltage went back up to 8v but keeping the DMM measuring the voltage and it started to drop slowly.


Did the same with the 33k resistor, voltage still fluctuates.


Any ideas?


Cheers,


David.

[jojokeo]

Are you using a power supply instead of a battery? What exactly are you using for the power supply?

[mayburyds]

Hi,


New 9v battery.


Cheers.

[jojokeo]

Something is definitely amiss - the only thing left is a wiring problem or similar? How about a few photos to see what the heck is up? All guesses are used up at this point. Confirming that there's no other pedals hooked up and it's not on a pedal board? The swaying voltage reading is not right either.

[mayburyds]

Hi,


I'll get some photos.


It's only guitar - FF - amp no other pedals involved.


Cheers.

[sluckey]

What kind of guitar? Active pickups? Do you still get the noise if you unplug your cord at the guitar?

FYI. Silicon and germanium transistors are biased differently. Voltage drops across the junctions will be different. Neither will be really happy in a circuit designed for the other.

[pompeiisneaks]

Oh yeah definitely a possible problem, you mentioned you had the Silicon one, you've replaced the silicon transistors with Germanium if you used the new NTE AC128's.  If you wanted to convert it to germanium (I hear they sound better supposedly), you could look at that link I referenced earlier and see how the components differ and adjust accordingly.  Maybe you should just do a kind of PTP setup in there with the old school germanium schematic.

~Phil

[mayburyds]

Hi,


No active pickups used.


I have converted to AC128s and switched the orientation of the electrolytic caps and the power supply.


From what I understand that apart from the above the circuit, components and values are the same for silicon and gemanium. Bias is 4.5v for both.


Since I made the conversion I have no noise issues just the voltage drift which could have been there with the silicon transistors but I was more focused on the noise issue.


I'll post some pictures today.


Cheers.

[mayburyds]

Hi,


Pictures as requested.


As you can see the board is getting a beating from all the component swaps. I had to extend the legs on the AC128s as they are a from an old FF kit. New AC128s should arrive today.


Cheers.

[mayburyds]

Hi,


New AC128s arrived and now the bias voltage is stable at 4.64!


Temperature issue with the other AC128s perhaps unless you can spot something in the pictures.


Anyway, thanks again for the replies.


Cheers,


David.

[Ed_Chambley]

Been away, gald to see you got a real Fuzz Face.  Looks good.  Should be ready for another Decade.

[mayburyds]

Ed,


Thanks.


Dug the following out of the cupboard! Bought it back in the day but wasn't keen, decided to give it another go.


Cheers,


David.