Can't get a Silicon FF Working

[Craig V]

Hi,

This is so frustrating, how I can never build something without having to debug it, even something as simple as a Fuzz Face.  Even after all the pedals I've built, I still feel like a complete beginner.  Maybe this hobby just isn't for me...

The pedal is a Silicon Fuzz Face.  I used BC109C transistors.  These are the metal can style, with the tab to indicate emiter.

Here are some transistor voltages, maybe someone can figure out what is wrong.

Q1:  E 0.0V  B .54V  C .99V

Q2:  E .59V  B 1.12  C  7.61V

I get a slight octave up effect high up on the frets.  The Fuzz control does nothing, and the volume control doesn't shut sound completely off when turned to zero.  Those are the symptoms. 


Thank you very much.  I appreciate any help.  If it wasn't for this board, I would have been done building pedals years ago.

[b_rogers]

which schematic are you using?  voltage on q2 is pretty high...


Brent

[Craig V]

Brent,

I'm using the schematic from Fuzz Central: http://fuzzcentral.tripod.com/fuzzface.html

I changed the 470 ohm to a 330 ohm, and reversed the power supply and cap orientations, since it's NPN, not PNP.

-Craig

[b_rogers]

hmmm try a larger resistor (10k possibly) for q2's collector or better yet a trimpot to get 4.5-5v. of course i would check all my solder joints, tranny orientation, pot wiring,  etc...hopefully getting the voltages correct will correct the problem.

hope this helps


Brent

[petemoore]

Q1:  E 0.0V  B .54V  C .99V

Q2:  E .59V  B 1.12  C  7.61V
  Q1 collector should be connected to Q2 base.
  Battery measured voltage puts these numbers in perspective.

[Steben]

I suspect a naughty naughty trimpot not showing up here... 

No really, make the collector resistor of Q2 a trimpot of 10kohms and turn the thing around. Normally a Fuzz Face can by biased by ear and playing without a mulitmetre. Did you buy a ready-to-build kit?

Once you know the how-to, FF's are easy.
There are people over here that have a daily FuzzFace biasing for breakfast... 

[Craig V]

Hi,


I swapped out the 8.2K for a 10K resistor.  Here are the new voltage readings:

Battery : 9.83V

Q1:  E 0.0V  B .55V  C 1.04V

Q2:  E .62V  B 1.04V  C 9.74V

When I plugged it in, I noticed it does not have nearly the gain I expected.  The "Fuzz" pot does not do anything at all, no matter where it's set it sounds exactly the same.  Also, when the "Volume" pot is put to zero, I still get sound through.  I just want throw this thing against a brick wall.  Is there anything odd about the pinouts of BC109C transistors that I do not know about?  I assume the tab coming out indicates emitter, so base is next to it, and collector the farest from emitter. 


Thank you all for your help.

[aron]

Check your pinouts. Here's a link on how to check it with a multimeter:

http://www.diystompboxes.com/smfforum/index.php?topic=22724.0

[Craig V]

I used the method Aron provided to test the transistors:

Testing with a (Digital) DMM
Set your meter to the diode test. Connect the red meter lead to the base of the transistor. Connect the black meter lead to the emitter. A good NPN transistor will read a JUNCTION DROP voltage of between .45v and .9v. A good PNP transistor will read OPEN. Leave the red meter lead on the base and move the black lead to the collector. The reading should be the same as the previous test. Reverse the meter leads in your hands and repeat the test. This time, connect the black meter lead to the base of the transistor. Connect the red meter lead to the emitter. A good PNP transistor will read a JUNCTION DROP voltage of between .45v and .9v. A good NPN transistor will read OPEN. Leave the black meter lead on the base and move the red lead to the collector. The reading should be the same as the previous test. Place one meter lead on the collector, the other on the emitter. The meter should read OPEN. Reverse your meter leads. The meter should read OPEN. This is the same for both NPN and PNP transistors.
As noted, some transistors will have built in diodes or resistors which can confuse these readings.

It passed the test, except for the last one, test the collector and emitter.  I got readings for both red to collector/black to emitter, and vice versa.  Does that mean anything?

Thank you!

[octafish]

Do you have a Hfe setting on your meter? If you do check your trannys for Hfe and go to:
http://www.diystompboxes.com/analogalchemy/emh/emh.html click on Fuzz-Face.
Or alternatively build the antiquity fuzz at joes site.
http://www.diystompboxes.com/analogalchemy/index.html

[Craig V]

Hi,

No, my meter does not measure hFE, unfortunately.  Although the gain of the transistors plays a big role, I think it should at least pass a fuzzy signal if it were working correctly?  Does the fuzz pot not doing anything indicate something?  There are no shorts or broken solder connections--the fuzz control just does nothing when I turn it.

Thank you.

[Craig V]

Update:

I noticed I had a slight error on the PCB.  The wire from VOL 3 went to the 100K/emitter junction, instead of the .01uf cap.  I switched those wires around, and cleaned the PCB.  Now what happens when I plug it is is an extremely gated effect.  Only at the slightest strums can a clear sound come through, the rest is very very gated. 

The transistor voltages:

Q1:   E 0.0  B .55  C  1.03

Q2:  E .62  B 1.03  C  9.63

Is the collector of Q2 way too high?  I would expect it to clip, but not become gated at this voltage. 

Any suggestions?

Thank you!

-Craig

[petemoore]

Q1:   E 0.0  B .55  C  1.03

Q2:  E .62  B 1.03  C  9.63
  I *think you're real close and only have to diddle with the Q2CResistor value [trimpot?] to get rid of the gateyness.
Is the collector of Q2 way too high? This is part of an equation for which the battery or supply voltage is neccesary to be worked.
   I would expect it to clip, but not become gated at this voltage.
   Q2C should be at around 1/2 the supply voltage.

[Craig V]

Pete,

I put in a 22k resistor (a 10K was in there already), and it brought the voltage down to 3.62V.  I plugged it in and now it works!!!  A great sound from such a simple circuit. 

Thank you to everyone, all your help is very very appreciated!!! 

Time to go AB it with my Ge FF.

Thanks again everyone!,

-Craig

[ErikMiller]

Congratulations!

Try a 15K resistor and see if you can get Q2's collector closer to 4.5V. That's really the center of the sweet spot.

That's a pretty high value to have to put in there to bias it, by the way. You might double check the values of the other resistors.

[Craig V]

Will do.  I might add a pot in there, probably a 20K.  It sound pretty good now, but I want to try and get it to 4.5V.

Thanks!

Craig