Fuzz face from Musikding: no way to make it work.

[freefrog]

Hi everybody,
Having already built several DIY FX's and having modded most of my stompboxes, I've ordered a silicon fuzz face kit from Musikding.

I was genuinely thinking it to be simple to do.

I've carefully mounted the whole, following their schematic.
The pedal didn't work.

I've took the thing, got a look in it, found an error in the layout, redone the whole.
It didn't work.

I've took the PCB, redone all my soldering, changed the footswitch for another one of the same model, measured EACH single component (R, C, voltage and so on) as well as each connection with my LRC meter.
ALL was normal.

But the thing stays silent.
I've obtained a sound of empty battery here and there.
I've also obtained a full sound of fuzz during 0.5 second, while I was pushing on the bias pot with my screwdriver. Then, nothing (even after a resoldering of the bias pot).

I'm stuck.

Help appreciated. Thx!

[Jazz P Bass]

You need to study the schematic & take some voltage readings.
BCE readings of the transistors would help.
Also measure the resistance of the bias pot.
It may be bad.
Kindly anotate the "error" that was found.

[freefrog]

You need to study the schematic & take some voltage readings.
BCE readings of the transistors would help.
Also measure the resistance of the bias pot.
It may be bad.
Kindly anotate the "error" that was found.

I've worked on it two full days and nights...

I've studied the schematic, and even redrawn manually the PCB with its tracks. No error found, except in THEIR layout - whose original draw was plugging the input hot point on the overall ground when the FX was bypassed !!!

I've checked resistances, capacitances. I've inspected each component (including the bias pot) as well as their connections. Nothing special

I've changed the diode: no difference.

Soldering a wire in parallel with one PCB track, I've seen the "empty battery" sound coming back. So, obviously, the quality of the PCB is not optimal... A short cut might have happened somewhere in it (?) but my multimeter says that the tracks are good.

Finally, I suspect the solid states, whose voltage readings are "strange". I think that one of them was simply DOA. I've vainly tried other solid states BUT that's old components that I have for 25 years and I don't remember at all if they were supposed to work or not... I'll buy a couple of new SS the next days.

Anyway, I appear to be out of luck these days: my main soldering iron has mysteriously got cold three times while it was plugged and one of my multimeters became mad.

Thx for the answer, nevertheless.

EDIT: have tested again the voltage between "base" and "emitter" in each SS: WHATEVER i put in Q1 and Q2, this voltage = 0.65v in Q2 and 0.25v in Q1.

The sound of "empty battery" remains, whatever is the power source used (9V battery or any 9V AC to DC adapter).

[Steve L]

You need to move one side of C3 for it to work.

Almost every schematic of a fuzz face floating around the internet has this same, very obvious error.
I hope it was not sold to you with instructions to build it to the schematic. Makes you wonder if it was ever tested.

C3 is the output coupling capacitor. It needs to connect directly to the collector of Q2, instead of the 9V power supply.
The other side of C3 that goes to the volume pot is correct.

By the way, if they have not already instructed you, RV1 needs to be adjusted so the output clips symetrically.
That is what seperates a good sounding fuzz face from a bad one.

Steve

[J M Fahey]

The schematic is fine, you are making some building error.

THEIR layout - whose original draw was plugging the input hot point on the overall ground when the FX was bypassed !!!

This is not an error.
The board input is grounded when not in use, to avoid it turning into a very annoying interference machine.
You need to move one side of C3 for it to work.

Almost every schematic of a fuzz face floating around the internet has this same, very obvious error.

It's not.
Those 330r are part of the Collector load, which is split in two (330r+R5 and whatever you set RV1 to) to lower ths signal level, which would be unbearably high otherwise.
The function of (non-original) RV1 is to change the sound character at will; FuzzFaces have a *very* unsymmetrical waveform output, and even if you could dial a symmetrical one at clipping onset, that instantly goes out of the window because the bias point changes wildly with signal level.
That's part of the magic
I think your problem is that you are mistaken with the "silicons" pinout, which you don't eve identify.
Post what they are, google their datasheet and the one which Musicding suggests.
If possible, scan both sides of the PCB to check for layout errors, although I doubt them.
Regular flatbed scanners scan boards beautifully, even if stuffed, they *do* have some optical depth of field.
Post Emitter, Base and collector voltage (relative to ground) for each transistor, we are talking 6 values in total.
Good luck and don't worry, we have *all* been there.
I still remember my frustration at a 2 transistor Reverb Driver and accompanying 2 transistor Reverb recovery preamp published in Popular Electronics around 1968, which I could *never* force into producing any sound.

[freefrog]

The schematic is fine, you are making some building error.

This is not an error.
The board input is grounded when not in use, to avoid it turning into a very annoying interference machine.
You need to move one side of C3 for it to work.

I undestand what you're saying, BUT...
In my (limited) understanding of hobbyist, their layout gives two position to the footswitch:
-either the guitar input (pin 2) is connected through pin 1 on the enter of the PCB (labelled '1'), which is fine.
-either the guitar input is connected to pin 3, itself connected to another pin 3 which goes to ground: the effect is therefore disabled BUT the input is grounded too. :-(
That's why I've connected the enter of the PCB on pin 2 and the guitar input on pin 1, which leads it to be connected to the output when the effect is bypassed (hope it's clear, I haven't the schematic under my eyes right now).

It's not.
Those 330r are part of the Collector load, which is split in two (330r+R5 and whatever you set RV1 to) to lower ths signal level, which would be unbearably high otherwise.
The function of (non-original) RV1 is to change the sound character at will; FuzzFaces have a *very* unsymmetrical waveform output, and even if you could dial a symmetrical one at clipping onset, that instantly goes out of the window because the bias point changes wildly with signal level.
That's part of the magic
I think your problem is that you are mistaken with the "silicons" pinout, which you don't eve identify.
Post what they are, google their datasheet and the one which Musicding suggests.
If possible, scan both sides of the PCB to check for layout errors, although I doubt them.
Regular flatbed scanners scan boards beautifully, even if stuffed, they *do* have some optical depth of field.
Post Emitter, Base and collector voltage (relative to ground) for each transistor, we are talking 6 values in total.
Good luck and don't worry, we have *all* been there.
I still remember my frustration at a 2 transistor Reverb Driver and accompanying 2 transistor Reverb recovery preamp published in Popular Electronics around 1968, which I could *never* force into producing any sound.

Thx to you and to Steve L for these instructive answers. :-)
I'll also try a couple of brand new SS and I'll see what happens. If necessary, I'll "second" each PCB track with a parallel wire...

[Jazz P Bass]

Uhmm.
You still did not take any voltage readings.

[freefrog]

Uhmm.
You still did not take any voltage readings.

Sorry... Was in reheasal yesterday and I'll be stuck at work today.
Have measured the voltage between base and emitter: whatever is in Q1 and Q2, the results are 0.25v for Q1 and 0.65v for Q2.
Then my multimeter has stopped to work because of an empty baterry. I have to solve this new issue before to do further measurements... Sorry again and thx for your help.

[R.G.]

I've seen so very many posts on various forums like this. The trouble is almost always (1) wrong component (2) incorrectly positioned component/pinout (3) bad soldering or (4) incorrect wiring. Just to save myself the typing, I wrote up: DEBUGGING - What to do when it doesn't work

I wrote it about six years ago. In that time, there are remarkably few problems that didn't get solved for people who'd follow the directions.

It's more than a set of debugging instructions. If followed, it often forces the builder to avoid making the same perceptual mistakes that prevent them from seeing a problem. Many people following this find their own mistake.

[freefrog]

I've seen so very many posts on various forums like this. The trouble is almost always (1) wrong component (2) incorrectly positioned component/pinout (3) bad soldering or (4) incorrect wiring. Just to save myself the typing, I wrote up: DEBUGGING - What to do when it doesn't work

I wrote it about six years ago. In that time, there are remarkably few problems that didn't get solved for people who'd follow the directions.

It's more than a set of debugging instructions. If followed, it often forces the builder to avoid making the same perceptual mistakes that prevent them from seeing a problem. Many people following this find their own mistake.

Thx for the link. I wish it was my error because if it's not, I'll have lost my money. :-)

Anyway, I must give up for the moment: I've way too much work and things to do right now. I'll try to rebuild the whole pedal from scratch the next month.

To be continued, so...

[Jazz P Bass]

I would seriously like to see you troubleshoot the circuit.
You have the schematic.
Test each & every point on the board to verify that it agrees with the schematic.
It may be something as "simple" as haveing a transistor installed backwards.
In this case, look up the transistor datasheet & observe what the pinout of the leads are.

[freefrog]

I would seriously like to see you troubleshoot the circuit.
You have the schematic.
Test each & every point on the board to verify that it agrees with the schematic.

I've done it: it agrees with the schematic...

It may be something as "simple" as haveing a transistor installed backwards.
In this case, look up the transistor datasheet & observe what the pinout of the leads are.

The transistors are properly installed...

That's precisely why I'm stuck.

But I humbly and sincerely thank you and those who have tried to help me.

To be continued...

See you later!

[J M Fahey]

Thx for the link. I wish it was my error because if it's not, I'll have lost my money.

Well, I guess in that case maybe you have not lost any money.
Please buy a new battery for your multimeter and post those voltages.

[Jazz P Bass]

Voltages to post:
Each transistor: C to ground/ E to ground/ B to ground.
This will tell if they are biased properly.

[freefrog]

ARGL...

Technical problems stack upon each other: now my old trusty main multimeter has problems since it exhibits non sense readings, even with a fresh battery and even with nothing connected to it (!). I'll have to open it too...

Two days ago, I've already been forced to repair my main soldering iron with its spare mate: the cable with prongs was smoking...

"Law of series", as we say here. A problem rarely comes alone...

So, destiny appears to force me to stop working on my FF kit. Anyway, my job is now calling me urgently.

Nevertheless, I fully appreciate the help offered here. I want to underline that Klaus Brunner, from Musikding, is also helpful and patient with my case.

See you later (in three weeks).