Fuzz Factory clone not behaving right questions

[StevieLaser]

Hi,

I've just built a Fuzz-Factory clone and I'm not sure if I got it completely right... I get sound out, and it will do many of the fuzz-factory behaviours, like self-oscillation and so on. But, I am finding that the gain control generally does almost nothing until the last 20% or so of its range. So, there's a pretty clean signal with the pedal on until I pass about 3o'clock on the gain knob, then it can get very fuzzy very quickly. Now, this can vary a bit with some of the other knobs, but I am almost always working in a very narrow range on this knob.

Now, I took a look at the ZVEX video to see how the real thing compares. The first thing he does is set it up to sound a bit like a Fuzz-Face by setting:
Vol: 9 o'clock
Gate: 7 o'clock (minimum)
Comp: 7 o'clock (minimum)
Drive: 2 o'clock
Stab: 5 o'clock (maximum)
When I set this I get no sound at all. The Comp knob pinches off the sound completely below about 8 o'clock. That doesn't seem right to me.

I've tried a few of the suggested settings from the Fuzz-factory settings list, but they don't sound like the name suggests to me.

I used the following layout:
http://2.bp.blogspot.com/_y4AYtND8Hz8/TCINTn3D6JI/AAAAAAAAAY0/wBxmQy75fJ8/s1600/knownworkingtotal.gif
I've not changed any components from the layout.

I am using two AC128s. I've not measured them myself, but the guy I bought them from provided Hfe and leakage numbers for each. So I have Hfe=61, Leakage = 0.08mA in Q3, and Hfe=101, Leakage=0.19mA in Q2.

I measured some voltages
Battery: 8.35V when not connected to circuit.
With the pots set up for the 'fuzzface' setting above:

Q1
C =8.2V
B =8.05V
E =8.25V

Q2
C=8.05V
B=8.14V
E=8.25V

Q3
C =7.45V
B =0.56V
E =0V

So, is this a case of all fuzz-factories are different, or is there something wrong here?

All advice would be much appreciated,
Steve

[LucifersTrip]

Firstly, I'd start by using a fresh battery.

Secondly, the voltages are way off. A transistor can't be doing any amplifying if EBC voltages are all the same.

It's definitely time to start checking wiring, shorts, etc, starting with the beginning around Q1 since EBC are all the same.

The closest voltages to something useable is Q3, but this is probably another that the collector should be around 4.5v (someone who's measured one, please confirm)...but no use adjusting that until you sort out the rest.

good luck


edit: (link for reference):
http://www.geofex.com/fxdebug/bias_prob.htm

[StevieLaser]

Thanks LucifersTrip, that looks like a useful reference for bias problem debugging.

I spent a couple of hours looking for shorts etc before I posted last night, but after I reached the limits of my attention span I posted here. I've had another couple of hours of that today with no luck. So, it is about time I tried to understand the circuit rather than just build blindly! The debug link above should help.

Can anyone suggest a schematic of the circuit that matches the layout I've just built? I've spotted a couple online already but there are some differences in the way the pots are wired from the layout I've built 

[Scruffie]

Thanks LucifersTrip, that looks like a useful reference for bias problem debugging.

I spent a couple of hours looking for shorts etc before I posted last night, but after I reached the limits of my attention span I posted here. I've had another couple of hours of that today with no luck. So, it is about time I tried to understand the circuit rather than just build blindly! The debug link above should help.

Can anyone suggest a schematic of the circuit that matches the layout I've just built? I've spotted a couple online already but there are some differences in the way the pots are wired from the layout I've built 

The layout is fine, I drew it from a copy of someone elses layout (can't remember whose... Igloo I think) but fixed the stab wiring.

I've built it twice from that.

[StevieLaser]

Sorry, I didn't mean to suggest that the layout wasn't good. Just that I've messed something up and that I now want to try and understand the circuit to help me debug (and for my own education)

[StevieLaser]

I checked again and found a fairly obvious error with the way the Comp pot was wired. I had it sortof backwards. Now I get sound with the comp pot fully anticlockwise, and it pinches off when fully clockwise (as described on the ZVEX site). But, the gain is still very low across most of the range of the gain pot, with everything happening in the last 25% or so of the adjust. So, still very different from the ZVEX demos.

Scruffle, could you confirm if I've interpreted your layout right for the Comp pot?

• I'm looking at the back of the vero board (copper showing, components on the other side), with the pots sitting above the board in the same orientation as your layout, looking at the back of the pots.
• I have a wire from A11 to the leftmost lug of the comp pot.
• The leftmost lug of the comp pot is also wired to the leftmost lug of the drive pot.
• The remaining two lugs of the comp pot are wired together, then wired to A17.

Thanks,
Steve

[Scruffie]

No... you're looking at the component side of the veroboard, the tracks & cuts show through... but yes you are looking at the back of the pots.

The pot wiring you are correct on though.

[MikeH]

Double check the orientation of your germs.  The voltages look sketchy to me- especially Q1

[StevieLaser]

Hello again,
So, after a couple of days off I've come back to looking at this thing again. Still can't find the problem and I think I'm going insane from staring at blobs of solder 

My issue is that while I can get lots of the right sort of sounds out of this thing, that the pots don't behave like the ones on the ZVEX demo. Most obviously, the gain pot does nothing until the last 25% or so of turning.

I haven't posted any voltages since I fixed the Comp pot a few days back, so here is what's going on now:

Pots are set up as in the ZVEX video 'Fuzzface' setting
Vol 5 o'clock (max)
Gate 7 o'clock (min)
Comp 7 o'clock (min)
Drive anywhere (makes no difference to the DC voltages at the transistors)
Stab 5 o'clock (max)

Q1 (PNP AC128)
C =1.72V
B =8.33V
E =8.40V

Q2 (PNP AC128)
C=8.33V
B=9.05V
E=9.18V

Q3 (NPN 2N3904)
C =8.18V
B =0.57V
E =0V

Could someone who has built one of these post their voltages to compare? Or if anything strange jumps out at anyone from these numbers I'd appreciate any suggestions.

Cheers
Steve

[the3secondrule]

Scruffle, could you confirm if I've interpreted your layout right for the Comp pot?

• I'm looking at the back of the vero board (copper showing, components on the other side), with the pots sitting above the board in the same orientation as your layout, looking at the back of the pots.

No... you're looking at the component side of the veroboard, the tracks & cuts show through... but yes you are looking at the back of the pots.

The pot wiring you are correct on though.

[/list]

[Nostalgia]

Bumping up this old thread. Same problem to my Fuzz Factory build. I can only get that high gain at the last 20% of the drive pot. Transistors used are sylvania spam cans. Q2 is 120hfe and Q3 is 135hfe. Sounds really amazing and in par with my Jerms SpamFactory.