1st Build: A Si Fuzz Face

[JRM]

Hi,

I've managed to build my first project: a Fuzz Face clone. I've used the Si NPN version (negative ground) on a stripeboard and managed to put it working.
Yesterday I've connected it to my Strat (3xSingle coil Texas Special) and small valve amp (Laney Cub10) and the results were mixed:

• At low volume and gain there's no effect at all; just a volume attenuation if I don't open the effect volume pot all the way
• Raising the volume of the amp and one can hear a remarkable tone difference! But no distortion. Of course that if I raise the gain of the amp I get distortion, but that happens allways, with or without the effect. I didn't had the time to test if it really breaks up sooner with the effect or not, it was just 10 minutes to check if it really works
• I got a terrible noise issue! I don't know if it's the grounding or an interference with the pickups (it got worse when I approached the axe while I was playing with the pots). All the ground connections are OK, I was feeding the circuit from a 9V battery (rechargeable); oddly enough it got better when I touched the amp
• I got a radio station emission! That was weird! The effect isn't placed in any enclosure yet as it will be part of a pedalboard with several effects

Is there anything I should look for about the noise issue and the apparent lack of effect?
Trannies hfe are Q1=325 and Q2=380; Meanwhile I've bought 3 more BC109B for another project and measured their hfe (306, 370, 395). I might change Q1 to the lower hfe I have (it's less than 10% but it's lower) and either leave Q2 unchanged or lower it too. What do you think about it?

[smallbearelec]

Something is not wired right. Once you get it wired right, you will want to try lower-gain devices and tweak the bias to reduce the harshness.

--Read "What to do when it doesn't work" for troubleshooting tips.

--Some people find it helpful to breadboard; here are the links to my references on breadboarding the Si FF:

http://www.smallbearelec.com/HowTos/Breadboarding/BreadboardIntro.htm
http://www.smallbearelec.com/HowTos/BreadboardSiFF/BreadboardSiFF.htm

The companion project:
http://www.smallbearelec.com/Projects/FurFace/FurFace.htm

Has notes on what voltages to expect where and how to measure them.

Good luck, and let us know how it goes.

Regards
SD

[lazerphea]

Hi,

I've managed to build my first project: a Fuzz Face clone. I've used the Si NPN version (negative ground) on a stripeboard and managed to put it working.
Yesterday I've connected it to my Strat (3xSingle coil Texas Special) and small valve amp (Laney Cub10) and the results were mixed:

• At low volume and gain there's no effect at all; just a volume attenuation if I don't open the effect volume pot all the way
• Raising the volume of the amp and one can hear a remarkable tone difference! But no distortion. Of course that if I raise the gain of the amp I get distortion, but that happens allways, with or without the effect. I didn't had the time to test if it really breaks up sooner with the effect or not, it was just 10 minutes to check if it really works
• I got a terrible noise issue! I don't know if it's the grounding or an interference with the pickups (it got worse when I approached the axe while I was playing with the pots). All the ground connections are OK, I was feeding the circuit from a 9V battery (rechargeable); oddly enough it got better when I touched the amp
• I got a radio station emission! That was weird! The effect isn't placed in any enclosure yet as it will be part of a pedalboard with several effects

Is there anything I should look for about the noise issue and the apparent lack of effect?
Trannies hfe are Q1=325 and Q2=380; Meanwhile I've bought 3 more BC109B for another project and measured their hfe (306, 370, 395). I might change Q1 to the lower hfe I have (it's less than 10% but it's lower) and either leave Q2 unchanged or lower it too. What do you think about it?

For what concerns lack of distortion, I'd check the transistors, if they're correctly oriented or if some of them is dead.
for the noise problem, maybe it could be a ground loop?

[JRM]

Thanks!
I've used the "search" to find out the expected voltages but haven't found it.
I've checked many times and all looks well conected. Polarities, everithing. I'll check it again.
Ground loop? I've just conected the ground of the in jack to the board and then conected the ground of the in jack to the ground of the out jack. I'm using high quality instrument cables (Klotz La Grange low capacitance cables with Neutrik jacks).

[deadastronaut]

@jrm

heres my 2p worth...if its even worth that..

replace 8.2k with a 10k /trim or pot/with a 4.7k on its outer lug ...on Q2 ..this gives a much better 'sweet spot finder'
(a brilliant pete moore method). (dont know why nobody has redrawn the schematic for this as it seems a common problem..)

as for noise...use a shielded input lead , when u finally box it...this will help with radio etc..

and as for power, you say its going to be part of a multi fx...so  i would use the psu instead of a battery
IF thats what your going to use in the end......you can get  different results with a  battery compared
to the psu you will eventually use..voltage sag etc.....so i would fine tune it with its eventual psu to be sure of tweaked value!.

[LucifersTrip]

I really don't think you should even worry about the noise issue until you actually have it wired/biased correctly and actually get a fuzz.

As smallbearelec wrote, you'd probably want to use lower gain transistors...probably in the 200 range to start.
You can find some voltage help here:
http://www.geofex.com/fxdebug/bias_prob.htm

On the FF, it's common to shoot for a 4.5 v for Q2 as smallbearelec also pointed out in the link he gave you (Read "It Still Doesn't Sound Quite Right":
http://www.smallbearelec.com/HowTos/BreadboardSiFF/BreadboardSiFF.htm

And lastly, what's the exact schematic you used?

good luck

[JRM]

Well, first of all I've used a schematics available at Fuzz Central which is exactly the same as the one used at Smallbear. I've managed to measure and the Q2 Vc is only 3,05V. To reach the 4,5V I'd have to decrease the 8,2k resistance to a 6,2k resistance. Let's see what happens when I have the time to do it. On the trannies hfe issue I'll work after. I think I might replace Q1 with a BC108 (lower gain). Or I might replace them both, I'll see it later.

I just had the chance to play and... We've FUZZ! 
On the other hand I got a quite harder distortion than expected! Maybe it's the too high gain of the trannies (307 and 325). I'll try with lower gain to find out which ones I prefer (I'm glad I've socketed that transistors). The noise issues are better: when I plug in there's no noise. I still get the radio station if the guitar amp is below 5. A quite nice (and expected) effect is that we can go back to a clean sound just cutting the axe volume a little bit (halfway between 8 and 9 is enough).
Problems still to solve:
- if I increase too much the Fuzz I get a very high and unpleasant noise (it's like permanent distortion even if I'm not playing); I can't describe it better because I've always turned it off as fast as possible to avoid damage on the amp speaker;
- interference.

[brett]

Trannies hfe are Q1=325 and Q2=380; 
Assuming you want a real fuzzface, either piggyback them (search forum for method) or just buy 2N2369A/BD139/TIPXX/MJEXXXX or something with hFE much less than 200.

[LucifersTrip]

To reach the 4,5V I'd have to decrease the 8,2k resistance to a 6,2k resistance.

remember, a 10K pot there is cool.

I just had the chance to play and... We've FUZZ!

excellent!

Problems still to solve:
- if I increase too much the Fuzz I get a very high and unpleasant noise (it's like permanent distortion even if I'm not playing); I can't describe it better because I've always turned it off as fast as possible to avoid damage on the amp speaker;
- interference.

You can many times remove noise/interference with strategically played caps and/or resistors....though caps are the most common.

Though I've had luck with caps in other spots I chose randomly, I was given this specific recommendation from earthtonesaudio that worked wonders:
For FF place cap between collector and base of the first or second transistor, or between the base of the first transistor and the emitter of the second transistor.

It killed all the noise without effecting the tone.  
Use a  small cap (.0001 - .0005 uf). Though I've used up to .001 uf

good luck

[JRM]

Thanks for all the tips. I'll definitely change the 8k2 resistance by a 10k trimpot.
Regarding the gain of the transistors there's something that still needs further investigation: I don't know the test current and voltage. And this is important as the gain will vary largely with those factors. For instance, the used BC109 have a gain of 40 to 150 at Ic=10uA/Vce=5V but also have a gain of 200 to 450 at Ic=2mA/Vce=5V. I know that I now have a Q1=307 and a Q2=325 gain but I don't know what are the measurement conditions (never had the multimeter manual).

[Electric Warrior]

Trannies hfe are Q1=325 and Q2=380; 
Assuming you want a real fuzzface, either piggyback them (search forum for method) or just buy 2N2369A/BD139/TIPXX/MJEXXXX or something with hFE much less than 200.

That's not high for a silicon fuzz face. They used BC108Cs back in the 70's. Hfe was 420-800 according to the Telefunken datasheet.
Before that they used BC183Ls (hfe could have been from the complete range of gains) and BC183KAs (those were low gain indeed. ranged from 120 to 220, but they only used them for a short while in 1969)

[tasos]

check that your volume of your instrument is full up....sometimes you get little distortion when the signal is low....well this is so anoying but what can we do?

[JRM]

check that your volume of your instrument is full up....sometimes you get little distortion when the signal is low....well this is so anoying but what can we do?

That's not anoying that's nice! It's an instant way to switch from clean to overdrive!

Regarding the hfe issue: well the Si Fuzz Face were built with BC108 and BC109 that have higher hfe than the Ge versions.

[JRM]

What could be quite nice to know is the current Ic that one should head to or the real gain in actual conditions. What do I mean by this? Well, the Fuzz Face doesn't work at the voltages and the currents that are used to test transistors hfe. In fact the Fuzz Face trannies are subjected to low Vce and low Ib meaning that the real (actual working conditions) of the transistors will be much lower than the usual Vce=5V, Ic=2mA or even higher test voltages and currents.

[Electric Warrior]

check that your volume of your instrument is full up....sometimes you get little distortion when the signal is low....well this is so anoying but what can we do?

That's not anoying that's nice! It's an instant way to switch from clean to overdrive!

Regarding the hfe issue: well the Si Fuzz Face were built with BC108 and BC109 that have higher hfe than the Ge versions.

The ones with BC109Cs were the the first reissues (late 70's) The last ones of the original run had BC209Cs, btw..

[JRM]

Yes. And BC109C have higher gain than BC109B. That's the difference between the "B" and "C", the gain range.

[Electric Warrior]

exactly!