Fuzzface noise (Silicon NPN negative ground)

[Outlaws]

I am starting a new thread for this problem since I got the thing working now.

I am getting a awful noise though.

When I start hiting power cords (hard) the noise stops for a second, then comes back.  But this is louder than just feedback.

http://www.berntson.us/guitar/zipper.mp3
(you might want to turn your speakers down, then raise the volume. YOu have been warned. lol)

[mojotron]

That's a bias issue on the collector of Q2 - I have heard this before. If you used a pot for the collector of Q2, adjust that. If not, you might want to use a pot to get the right value....  

Also, check to make sure you have a cap on the output before the output pot... that might do this as welll..

[Outlaws]

That's a bias issue on the collector of Q2 - I have heard this before. If you used a pot for the collector of Q2, adjust that. If not, you might want to use a pot to get the right value....  

Also, check to make sure you have a cap on the output before the output pot... that might do this as welll..

Thanks for the answer.  Sounds like you are really sure of this.  Thats nice to hear.

I do have a cap on the output before the pot.  Its the 22uF.

As for using a trim pot for the bias....here is my layout I am using.  Everything is the same except I am using a 330 in place of the 470.
Is the trim pot going to replace the 8.2k?  Or does it go inbetween them?

[Outlaws]

Anyone?

[smashinator]

Is the trim pot going to replace the 8.2k?

Yes, use it instead of the 8.2k and all will be laid to fuzzination upon twiddling.  You'll probably find playing with the trim pot rather amusing.   You can clean it up, or go dirtier by just tweaking that pot.

[Outlaws]

So trim pots have 3 leads...  does one go to ground or do I connect 2 together?

Also, I used a trim on my SparkleBoost (which is still a work in progress), and I don't see how I could fit it in the breadboard without an adaptor.  The leads/lugs are not really shapped to be bended to reach the target holes...let alone fit in the holes.

[petemoore]

You want V/R somewhere between around 8k2...say 5k6 -10k ...something likethat.
 Use the DMM Resistance checker to see what pots do.
 take a 20k or so pot, replace Q2's collector resistor [8k2?], with the pot.
 To wire a pot as V/R [variable resistor] use lugs 1 and 2.
 Or use lugs 2 and 3.
 For added  'safety' or something, connect the unused potlug to the wiper [lug 2].
 I use the DMM to verify I'm getting V/R around the range of 8k2...
 4k7 and 5k pot? ... whatever it takes to get Q2 collector near 1/2 of supply voltage [4.5v of 9v]...or the Q2 bias voltage you prefer.

[Outlaws]

You want V/R somewhere between around 8k2...say 5k6 -10k ...something likethat.
 Use the DMM Resistance checker to see what pots do.
 take a 20k or so pot, replace Q2's collector resistor [8k2?], with the pot.
 To wire a pot as V/R [variable resistor] use lugs 1 and 2.
 Or use lugs 2 and 3.
 For added  'safety' or something, connect the unused potlug to the wiper [lug 2].
 I use the DMM to verify I'm getting V/R around the range of 8k2...
 4k7 and 5k pot? ... whatever it takes to get Q2 collector near 1/2 of supply voltage [4.5v of 9v]...or the Q2 bias voltage you prefer.

I know how to check for 4.5v....but I don't know aobut  finding the range of 8k2.  is there a symble (other than just ohms) on a DMM I should look for?  Or do I put it on the nearest number to that?  The closest on mine is 2k and 20k.

Now about the first thing you said.... 5k6 to 10k....
I have a spare 4.7k and a spare 10k resistor....would they be possible feasable subsitutes for a pot?  Assuming they do properly bias it.

[Outlaws]

It looks like right now I am getting ruffly 8.98v when I use the multimeter on the 20v setting with the positive connected to collector.

[Outlaws]

Just got back from the store.

Got a 20k HighRel trimmer.  (a bit bigger...well, a lot bigger...than the last trimmer I had, but it should still be find on my board)

Also got 2 2N2369 transistors so that I can test on in Q1, and if it sounds good, I can use it, and use the other one and the original Q1 NTE123A as Q2 in a second Fuzzface.

Also my trim pot doesn't fit in my bread board except for one way...and that way involves the two pots on the one side to be in the same row ... ie connected.  I hope those are the two that need to be connected.  lol  (pictures in a sec)


Question.

Will changing Q1 to this lower hFE change my current bias problem in Q2?

[Outlaws]

As you can see, I color coded the lugs for easy reference.

In my breadboard, it looks like Red and Blue will have to be connected together becuase that is the only direction they will fit into the breadboard holes.  They are too close together to cross any gaps.


But aside from that issure, which lugs go where?

[Outlaws]

My last pedal used the trimmer like this...

Red was taking the power supply, and the other two went to the transistor.  I was able to bias it at 4.5v


I am trying this one in the same manner with the Yellow and Blue connecting to the tranny, but it isn't changing the bias at all.  Its just sits at about 8.8-9v.