Silicon Fuzz Face Biasing problem

[raccoondad]

I have built 2 different NPN silicon fuzz faces from different vero layouts and on both I am unable to bias the Collector of Q2. The lowest I can get is 6.7V and that's with a 100K pot!!! The fuzz sounds strange and super gated and nothing like any clips of a fuzz face I've ever heard. Because it has happened with 2 different builds I'm thinking maybe it's an offboard wiring problem? Has anyone else had this problem?

[GammaFlex]

What are your other values? did you change anything around regarding the voltage divider?

Gated sounds as far as I know are indications of a misbiased transistor.

Edit: Also did you use the FuzzCentral info?

[midwayfair]

I have built 2 different NPN silicon fuzz faces from different vero layouts and on both I am unable to bias the Collector of Q2. The lowest I can get is 6.7V and that's with a 100K pot!!! The fuzz sounds strange and super gated and nothing like any clips of a fuzz face I've ever heard. Because it has happened with 2 different builds I'm thinking maybe it's an offboard wiring problem? Has anyone else had this problem?

Post links to the vero layout and schematics you used.

Post voltages taken on each pin of the transistor, not just the collector.

Pics will help, too, particularly of both sides of the vero to make sure you've made all the cuts correctly.

Otherwise we're just guessing.

[raccoondad]

Vero layouts used:

http://tagboardeffects.blogspot.com/2013/04/creepy-fingers-effects-si-fuzz-face.html

http://aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=10880&g2_serialNumber=2

I will measure and post voltages on other pins when I get home from work (heh).

I used the continuity checker on my DMM to check my traces before I soldered, but I will check them again.

Pictures of the Aron Nelson build. Please excuse the messy wiring.

http://tinypic.com/r/2vt5nva/8

http://tinypic.com/r/hve4xj/8

I really appreciate any and all advice!! I posted mostly because I thought having the same problem in 2 different builds odd, and maybe there was something unique to the fuzz face circuit that I wasn't grasping. Always a chance I'm just a doofus though.

[raccoondad]

Voltages:

Q1
C - 1.13
B - 0.58
E - 0

Q2
C - 9.25
B - 1.13
E - 0.69

Transistors are 2n222. Running off of 1spot adapter at 9.37 V. Bias pot adjusted to 10k.

[raccoondad]

Ordered a Hipster PCB. Will update once built.

[sturgeo]

Are you able to measure the hfe of the transistors?

When i started out i had this with almost all fuzz face variants i built and found this calculator to be a great help:
http://www.diystompboxes.com/analogalchemy/emh/emh.html

Edit: From that page click on Fuzz-Face on the left

[midwayfair]

Pictures of the Aron Nelson build. Please excuse the messy wiring.

Unfortunately, that may be part of the problem. You have a lot of exposed wire on one side, and you could have the wires touching. It's hard to tell.

The good news is that everything EXCEPT your Q2 collector is pretty normal for a silicon fuzz face. however, it may help to know that unless the Hfe of Q2 is higher than that of Q1, you might not be able to bias correctly.

The first thing I'd do, though, is set your multimeter to continuity. Get out a fuzz face schematic, and systematically go through the pedal testing every connection -- make sure not only that things are connected properly but that you don't have a short to something that SHOULDN'T be connected.

Also, it's difficult to troubleshoot something when you've boxed it (rock it before you box it!). Make things easy on yourself: You can use something as simple as a breadboard and a few jacks for a testing rig, which is a $5 investment in less frustration in the future.

[raccoondad]

Take 2 - breadboarded. Q1 HFE is around 230, Q2 HFE is around 350. Both are 2N222. Same problem as before. Used the Smallbear guide (https://www.smallbearelec.com/HowTos/BreadboardSiFF/BreadboardSiFF.htm)
Went through schematic and checked part values. No luck, still incredibly stuttery, cuts out, unusable fuzz with an unbias-able C for Q2.

With Fuzz pot maxed and bias resistor for C2 set to 8.2K:

Q1
C - 1.2 V
B - 0.6 V
E - 0.0 V

Q2
C - 8.6 V
B - 1.2 V
E - 0.73 V

http://tinypic.com/r/mkgpww/8
http://tinypic.com/r/fmlgj/8
http://tinypic.com/r/2utnvvp/8

Am I doing something fundamentally wrong here?

[sturgeo]

These circuits were designed way back when transistors had much lower hfe values, this has to be taken into consideration when using new NPN silicon trannies.

For a test try changing R1 to 12k, R3 to 220r and R4 to 4k7

[raccoondad]

Tried the different resistors, no luck. Still can't bias Collector of Q2.

[GammaFlex]

I'd try a different transistor, with this much effort and still nothing that'd be the next thing I'd try.

[midwayfair]

There are no mistakes on your breadboard that I can see.

Your Q1 collector is a little high, even though that's normal for a silicon fuzz. Try sticking a 100K pot in place of the 33K, and try adjusting that resistor a bit. I'm suggesting using a pot because it can be really finicky.

You can also test out the transistors individually on the breadboard to see if they're functioning. If it's a dead part, then no amount of fiddling with the circuit will work. Just put a 1M from the base to collector, 470K from the base to ground, a 10K from the collector to +9v, and ground the emitter. You should get a really big boost and a collector bias of about 6V. If you don't, there's probably something wrong with the transistor.

[raccoondad]

Thanks for the suggestions everybody. Update: I populated the madbean hipster (silicon fuzz face) PCB and ran it through the breadboard testing rig and it is working properly! I am able to bias the collector of Q2 to suggested values (4.5-5.5V) and it sounds more along the lines of demos I've heard.

The fuzz pot works normally for the first 80% or so of it's rotation, but for the last 20% it gets super hissy and static-y sounding. For all settings the distortion is still pretty harsh, much harsher than something I would want to use... but I do get clean up with the volume knob so that's something.

I think these new concerns are a matter of playing with transistor and resistor values, but feel free to correct me if I'm wrong.

Also on my list is to determine what went wrong with the breadboard circuit, which should be a bit easier now that I have a working circuit for comparison.

[sturgeo]

Glad to hear you've had some success   

I'm guessing you're using a 1kB for the fuzz pot, having all the fuzz in the last 10-20% is normal behavior. I use a 1kC now on fuzz face variants as it gives a much more usable control over the entire pot range.

It does still sound like the transistors aren't quite biased properly but as you say, tweak some of the values and try different transistors till you get it to sound how you like it.