Author Topic: Fuzz Face not biasing correctly  (Read 3291 times)

bt2513

Fuzz Face not biasing correctly
« on: September 13, 2010, 04:13:59 PM »
My GGG 60's Fuzz Face (PNP) is not biasing correctly with Ge transistors.  It biases just fine with the supplied Silicon PNP transistors (4.5v with the R5 trimmer right in the middle).  When I put a Ge in Q1, I can't get it to bias lower than 7.5v or so.  Right now, I have a Si in Q1 and an AC128 in Q2 and am able to get it to bias at 4.5v... what gives? 

petemoore

Re: Fuzz Face not biasing correctly
« Reply #1 on: September 14, 2010, 09:05:32 AM »
When I put a Ge in Q1.
  Appears to give wierd bias...I think this may nail it.
  What are the 'specs' of the transistor ? [Leakage and gain.
  GEO Again, Technology of the Fuzzface article and related choosing germanium transistors with transistor measureing circuit.
 
Convention creates following, following creates convention.

bt2513

Re: Fuzz Face not biasing correctly
« Reply #2 on: September 14, 2010, 06:55:14 PM »
I have not been able to test for leakage and gain... I don't have the necessary resistors at the moment to do it.  I tried chaining a few together to get close to the values needed but still wasn't able to get an accurate reading.  The person who sold them to me tested them and they measured in the range of 50-150hfe but who knows.....

R.G.

Re: Fuzz Face not biasing correctly
« Reply #3 on: September 14, 2010, 06:57:33 PM »
My GGG 60's Fuzz Face (PNP) is not biasing correctly with Ge transistors.  It biases just fine with the supplied Silicon PNP transistors (4.5v with the R5 trimmer right in the middle).  When I put a Ge in Q1, I can't get it to bias lower than 7.5v or so.  Right now, I have a Si in Q1 and an AC128 in Q2 and am able to get it to bias at 4.5v... what gives? 
A fuzz face cannot NOT bias itself incorrectly nor refuse to bias correctly. It relies on you. What gives is that there is something you don't understand about what it's doing.
R.G.

Quick IQ Test: If anyone in a governmental position suspected that YOU had top-secret information on YOUR computer, how many minutes would you remain outside a jail cell?

bt2513

Re: Fuzz Face not biasing correctly
« Reply #4 on: September 14, 2010, 07:12:49 PM »
My GGG 60's Fuzz Face (PNP) is not biasing correctly with Ge transistors.  It biases just fine with the supplied Silicon PNP transistors (4.5v with the R5 trimmer right in the middle).  When I put a Ge in Q1, I can't get it to bias lower than 7.5v or so.  Right now, I have a Si in Q1 and an AC128 in Q2 and am able to get it to bias at 4.5v... what gives? 
A fuzz face cannot NOT bias itself incorrectly nor refuse to bias correctly. It relies on you. What gives is that there is something you don't understand about what it's doing.

Thank you R.G.  That was very helpful. 

In all seriousness, I know you are very respected around here and I, personally, have garnered much of my knowledge of DIY effects from information you have freely made available on the web.  However, I am also completely aware that there is obviously something happening within my fuzz face circuit that I do not completely understand.  What I could really use is any information that someone on this forum may find relevant to me as to why this would happen and how/if it can be remedied... or is it even a problem at all.

This is definitely not my first build and although I've spent numerous hours reading over articles, instructions, and message board posts, I do this as a hobby, not a day job, and thought that it was time that I simply asked a question.

If you didn't mean the tone of your post to sound so condescending, just say so.  Otherwise, I would appreciate any help that any other knowledgeable forum member may have to offer me.


Govmnt_Lacky

Re: Fuzz Face not biasing correctly
« Reply #5 on: September 14, 2010, 07:26:29 PM »
With all due respect to the forum gods, I understand where you are coming from. Not all of us have been doing this for years or are EEs for that matter. Sometimes the explanations leave me with more questions too. You are not alone!
Now for the problem. It seems to me that if you can get Q2 to bias then it should just be a matter of swapping Ge transistors. If it will bias in Q2 but not in Q1 then you obviously have a circuit problem. If the "good" Ge will bias in both, then you have a bad Ge transistor.
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of ‘up to and including my life.’

bt2513

Re: Fuzz Face not biasing correctly
« Reply #6 on: September 14, 2010, 07:58:41 PM »
Thanks for the reply!

I tried switching a few around (I have 5 AC128s right now..) and couldn't get any to bias correctly when I used Ge's for both Q1 and Q2... I've tried all of them at least once in each position.  When I put the Si in Q1, the first two I tried biased just fine.  Again, I know that the transistors don't bias themselves, ahem, so to be clear, at R5's lowest setting, the voltage reading on the collector of Q2 was 7.4-7.5v.  From what I've read, the ideal reading should be around 4.5v.

One thing I wasn't clear on is whether or not the transistors' gain would make a difference on the voltage readings when I am biasing the pedal.  The GGG kit instructions make no reference to what the supplied transistors' gains are, only that the Q2 collector voltage should be 4.5v. 

R.G.

Re: Fuzz Face not biasing correctly
« Reply #7 on: September 14, 2010, 09:47:34 PM »
How about posting the schematic you used, the actual part values and the voltages on the devices?

The point I was making obliquely is that the components don't have wills and intents. They do only what their construction and the laws of physics let/force them to.

If they're not acting as expected, it's buried in the circuit - what connects to what, what values are there, and what voltages/currents result. That's what's really going on. Debugging is merely the process of measuring enough data to understand what is really going on versus what should be going on.
« Last Edit: September 14, 2010, 09:51:17 PM by R.G. »
R.G.

Quick IQ Test: If anyone in a governmental position suspected that YOU had top-secret information on YOUR computer, how many minutes would you remain outside a jail cell?

Govmnt_Lacky

Re: Fuzz Face not biasing correctly
« Reply #8 on: September 15, 2010, 08:00:55 AM »
Your best bet is to try to get the materials needed to measure gain and leakage of the Ge's. This will tell you whether or not you have good or bad Ge trannys for this circuit. If they all measure good, then you may just have to install them and bias them by ear.
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of ‘up to and including my life.’