First post, first non-kit build. Hideous Fuzz Face buzzy-hiss.

[masinyourface]

This is my first non-kit build, and because of the small part count, I decided to attempt a Fuzz Face. Not wanting to mess with the leakage of germanium transistors, I decided to use silicon transistors.
(Q1-2N3904 & Q2 2N5088)

Long story short, there is a hideous buzzy-hiss when the fuzz pot is turned up most of the way. Turning it up all the way makes it even worse, but it seems to go away when I turn it down. The only other mods I've made besides the transistors is a 10K pot rather than 1K for the fuzz pot, and a 0.1 µF output capacitor rather than a 0.01 µF, and a 22µF capacitor on the fuzz pot rather than a 20µF.

I'm guessing the problem is originating from the 22µF cap on the fuzz pot. I've taken the cap out and the buzz goes away, but then I can't change the fuzz amount. I've even tried replacing it with different caps just to make sure it wasn't a bad cap, but that hasn't helped at all.

Any ideas?

[LucifersTrip]

1st, here's the debug thread
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

the transistor lug voltages are the most important for debugging.

The 10K fuzz pot will make a bigger difference that the 22uF, which will do almost nothing. The .1uF will only make it bassier.

suggestions:
1) get the voltages to make sure the transistors are biased correctly...~4.5v on Q2C
2) small call (~100-200pf) across B-C of Q1 or Q2
3) put 1K-2K resistor across outer lugs of pot to bring it down to size

good luck

[petey twofinger]

not really related to your problem here , but for future reference and as a reminder to myself (lol)  , i think this may be helpful to some .

sometimes the simple stuff can get fudged and overlooked . i find that is almost always the case with my problems , something really silly , NOT the actual parts / layout . i am guessing that you have already eliminated the simple mistakes that could be made before posting , a few thing to look out for that i ran into  .... check to make sure you dont have the polarity flip flopped on either the in or the out , try a different ps , like a fresh 9volt , look for cold joints / try jumpering with a probe , ie , eliminate the easily over look-able goofs before removing parts or 'freaking out" (like i do)  ... i need to develop a little more confidence cause its almost always , i did something stupid when setting up the first test / vs i made an error on the populating stage . then there is the " i forgot ONE trace cut or jumper " lol ... and the ever popular " the transistor need to be flip flopped"

BUT checking voltage on the transistor , that should happen very early in the debug stage as well .

if you are going to continue in this venture i would HIGHLY suggest you invest a lil time and very little $ and throw together a quick and dirty test oscillator , with the audio probe as well . i am still kicking myself for not doing this sooner . best tool i have next to my mini needle nose .

http://www.youtube.com/watch?v=6X7VrcYwKM4

http://www.youtube.com/watch?v=SF0ZjDsYKas

welcome to diysb (i am noob here so , dont listen to me so much) good luck , and dont forget to post up what it was !

[smallbearelec]

Presuming that you wired it correctly, which is possible, those transistor are way too hot, i.e., too high in gain, to work well in the FF. Please check out this article:

https://www.smallbearelec.com/HowTos/BreadboardSiFF/BreadboardSiFF.htm

If you follow directions, you will learn to put together a silicon FF that is cheap and sounds very good.

Regards
SD

[masinyourface]

Update:

By the way, except for the few mods mentioned above, I'm using the original Fuzz Face schematic part for part.

-I placed a 1K resistor across the outer lugs of the 10K fuzz pot since I don't have a 1K on hand, not really much of a difference. I used a 10K to begin with knowing the Z-Vex Fuzz Factory was based off of the Fuzz Face and used a 10K in place of the 1K.

-I tried a small cap across the collector and base of both transistors; however, I couldn't really get it to work. Smallest caps I have are 12nF at the moment. When I put one on Q2, it took away the buzz, but my gain was greatly reduced and I lost a lot of tone. Tried wiring multiple 12nF together in series to lower the capacitance, but that didn't really help either.

I have a feeling the problem is centered around the fuzz pot itself. I took the 22µF capacitor out and the buzz went away. Additionally, no matter what the volume knob on my guitar is, the buzz volume stays consistent unless I turn the fuzz knob. The issue is when Q2's emitter is shorted to ground through the 22µF cap.

Also, I measured the voltages for both transistors, maybe this will shine a bit of light:

Q1
C-1.36V
B-0.64V
E-0V

Q2
C-8.72V
B-1.37V
E-0.82V

Luckily I'm using a solderless breadboard, otherwise this would be even more frustrating.

[masinyourface]

smallbearelec,

I sure wish I had a few extra transistors to swap out. Currently the only transistors I have on hand I actually got from you. The "Jellybean" Transistor Kit to be precise. Great value, great service. Many thanks.

So, down to business, would like to donate me the transistors you suggested??

[LucifersTrip]

smallbearelec,
I sure wish I had a few extra transistors to swap out.

tho, i totally agree with smallbear that lower gain si's are far better in FF's, that is not your problem

-I tried a small cap across the collector and base of both transistors; however, I couldn't really get it to work. Smallest caps I have are 12nF at the moment. When I put one on Q2, it took away the buzz, but my gain was greatly reduced and I lost a lot of tone. Tried wiring multiple 12nF together in series to lower the capacitance, but that didn't really help either.

that suggestion (100-200pf cap across BC)  takes away the harsh highs of si and softens the tone, closer to ge. unfortunately, if you use too large a cap, the fuzz is killed, as you found out. good idea to string caps together, but not good enough.

you're using 12nf = 12000pF
http://www.justradios.com/uFnFpF.html

8 of those in parallel gives you 1500pf...too large
http://diyaudioprojects.com/Technical/Electronics/parallel-resistor-calculator.htm

Also, I measured the voltages for both transistors, maybe this will shine a bit of light:

Q1
C-1.36V
B-0.64V
E-0V

Q2
C-8.72V
B-1.37V
E-0.82V

and this is your problem...Q2C should be ~ 4.5V.  check component values around that area (Q2) and check for bad wiring/wrong components. Otherwise, increase the 8.2K to lower Q2C voltage. You really should be able to do that with no larger than 20K. If so, then something's probably wrong...or transistor choice is way off (doubtful with the common ones you've picked).  Put the higher gain one in Q2

btw, did you remember to change the 470 to 330 for si?

sample voltages from GGG:

9 volt power supply 9v

Q1 Collector 1.4v
Base 0.6v
Emitter 0.0v

Q2 Collector 4.5v
Base 1.4v
Emitter 0.8v

[masinyourface]

btw, did you remember to change the 470 to 330 for si?

I did not. Swapped it out and it reduced the buzz somewhat. (Thank God for solderless breadboards!) Voltage changes are negligible (few hundredths of a volt).

I'll solder up a new pot in the morning to replace the 8.2K resistor and use as a bias pot. Thanks for the help!

[Gus]

If you are on a breadboard that could be your problem.  Don't expect any circuit with gain to be quiet on a breadboard.

A FF type circuit need to be inside a metal enclosure for shielding AND the LAYOUT and LENGTH of the wires matter a lot.

You need the right kind of gain control the value matters because it is part of the biasing.  Placing a 1K in || with the 10K is not a good "fix"

[LucifersTrip]

If you are on a breadboard that could be your problem.

his Q2C voltage is 8.27 !

You need the right kind of gain control the value matters because it is part of the biasing.  Placing a 1K in || with the 10K is not a good "fix"

not sure why not?  it'll change the sweep a bit, but he'll have 0K - .9K at the ends instead of 0K - 10K so max fuzz will basically be the same as with the standard 1K pot....and it really wasn't meant to be permanent, anyway

[masinyourface]

Update:

-I've re-biased Q2 to about 4.5 volts. The hideous buzz remained.

-I found some caps I forgot I had! 1nF caps. Put 4 in series to get 250pF across the collector and bass of Q2, and the buzz mostly went away, but it's still there. I can hear some 60 cycle hum, which leads me to my conclusion:



There's a power/grounding issue. The only mod I did to the power was a 220µF cap across +9V and ground, which shouldn't have an effect on anything. Even removed the cap momentarily just to double check. Tomorrow I'll try to debug it further, but at this point I'm just glad to be a step further in the right direction.

If you are on a breadboard that could be your problem.

Maybe. I was really wanting to get a good feel of the circuit and then add some mods to it before soldering it up and casing it up. Since the breadboard is only temporary, I wanted to be absolutely sure there wasn't a circuit issue causing the buzz before I move forward any.

You need the right kind of gain control the value matters because it is part of the biasing.  Placing a 1K in || with the 10K is not a good "fix"

not sure why not?  it'll change the sweep a bit, but he'll have 0K - .9K at the ends instead of 0K - 10K so max fuzz will basically be the same as with the standard 1K pot....and it really wasn't meant to be permanent, anyway

I was planning on doing a few extra mods later on, so I decided to get a larger pot value to experiment with. Sure, the taper will be a bit off right now, but at this point I'm only really concerned with the tonal possibilities. As soon as I get a solid circuit I'll worry about tapering in terms of actual onstage use.

[Jdansti]

Have you tried using a battery to see if the 60Hz hum goes away?

This might not be happening if you're just on the breadboard, but I'll mention it just in case.  If you have an adjustable temp soldering iron/soldering station, make sure it's off when testing.  Mine causes a lot of hum.

[LucifersTrip]

Have you tried using a battery to see if the 60Hz hum goes away?

This might not be happening if you're just on the breadboard, but I'll mention it just in case.  If you have an adjustable temp soldering iron/soldering station, make sure it's off when testing.  Mine causes a lot of hum.

+1 ...and certain lights (I think fluorescent) can buzz it...my kitchen light buzzes a bunch of my fuzzes

if the rest of the voltages are in line with the ggg example, you have a small cap across B-C, you have the 330 in there, and you've eliminated external electrical appliances & the power supply, then yep...time to do some more debugging...jack wiring, etc

[LucifersTrip]

I checked...it was actually the incandescent lights that cause the buzz...

[masinyourface]

Update:

I've applied most of the ideas given. The two things that have helped the most are a cap from base to collector of Q2 and using a 9V battery. The fluorescent lights didn't cause much buzz, but the ceiling fan did. Put it this way, I live in Texas. That fan isn't going to be turned off. Here's my question: when I end up casing it up, putting it on my pedalboard, and using a 9V wall wart, do you think the buzz will still exist? What's the best way to prevent this?

[Jdansti]

Maybe RG will see this and give his expert opinion, but in the mean time, here's my non-expert opinion.

If the noise is caused by RF, boxing it in a properly shielded enclosure and using shielded cables that are in good condition should help. If the noise originates in your PS, boxing it might not help. Be sure to watch for other power cords on the floor close to your PS and signal cables.

Also-after you eliminate as much of the RF and PS noise as possible, you might have some residual hiss that is inherent in high gain pedals.

[masinyourface]

I would love to get the great RG's opinion. The power supply I'm having problems with is after all one he had a hand in designing...the OneSpot has its advantages and disadvantages I suppose.

One thing I noticed is that even with a 9V battery in place of the OneSpot, I still get the buzz unless I have the Q2 capacitor between base and collector.