Axis Face gain control isn't really responding.

[liddokun]

Hi all,
I just finished building a Roger Mayer Axis Fuzz, part for part from the schematic off Fuzz Central.  The only
exception is instead of a 2N3906, I used a Ge PNP instead (replacing it soon).  The pedal works and everything, my only problem is that the
gain pot isn't very responsive.  I used  a 2k  linear pot like the schematic calls for.  At first, i was getting a slight gain boost (very slight...hardly noticeable) when I turned the pot counterclockwise.  Fixed this by switching wire from 1st to 3rd lug.  But I still only get a faint gain boost when using the pot.  Its barely even noticeable all the way down, or maxed out.  Is there a problem with my wiring?  How do I get the gain pot to respond better?
Cheers

[petemoore]

  Whats the V's.
  See the debugging thread.
  Sounds like it needs debugged.

[liddokun]

Hm, yes, I should get a hold of a meter and run it through.  I thought this may be a common problem, but I guess not.
I'll post voltages ASAP.

[kurtlives]

Fuzz Central suggests a 1KB pot. Though a common mod for germanium FF is to change this pot to 2K so I dont think this is your problem.

[liddokun]

Do you think it's the transistors? The Ge tranny I'm using isn't tested for gain, so maybe its that.  Any ideas on the source of the problem?  I don't have a meter at the moment, so maybe any common errors?

[kurtlives]

Your using a PNP transistor in a negative ground circuit. Is it wired for negative ground or positive?

Voltages?

[liddokun]

it uses a pnp and npn.  wired for negative ground.  I'll check voltages tomorrow, I don't have access to a meter, have to do it in school.  I guess there isn't much I can do now eh?

[liddokun]

I tried replacing the Ge pnp with a Si one.  Fixes the problem a bit, gain pot is more responsive, there is a definite increase in gain when it is turned now.  But I dont know how clean it should sound with pot all the way down.  Does anyone know?  Maybe it was a gain issue with the tranny. Still going to take voltages tomorrow.

[ambulancevoice]

i think whats happening is that the germanium transistor has alot of leakage and has very little gain if not none at all, so there is no fuzz, or because its pnp and not npn (i assume the circuit is negative ground positive supply, if not, pnp will not work with negative ground positive supply) the transistor didnt work with the circuit. and now that you put an (npn?) silicon transistor in there, which has alot more gain (what transistor did you use?) it works but has alot more gain now, so its harder to get a clean sound

[liddokun]

Well, when I had the Ge trannies in there, there was fuzz, enough for me to deem the effect functioning.  The level pot worked fine too.  It was just
the gain pot that basically changed the gain only a tiny bit from all the way down, to all the way up.
I use this schematic for the Axis Fuzz:


The circuit uses two Si tranisistors, one npn 2n3904 and a pnp 2n3906.  It's negative ground positive supply. 
At first I was assuming it was because of germanium leakage.  Taking voltages today.

[ambulancevoice]

axis fuzz??? it says axis face in your thing!
ok, never mind my post, it thought you meant the AXIS FACE

[liddokun]

Oh my, that was a huge mistake.  I can't believe I put that, but I think it's too late to change the post, and I don't want to start a new thread. 

[petemoore]

  Wiring mistake.
  A Dmm certainly does improve the debugging process, I should say enables the 'hard' 90% of it.

[liddokun]

What kind of wiring mistake?

[liddokun]

Ok, I went through my circuit with a DMM. 
According to the debugging thread, this is the info I need to list:

Build: Axis Fuzz, from Fuzz Central. (Schematic is shown above)

I built it part for part off the schematic, including the transistors. 
The only difference from the schematic is that for the 2k linear drive pot, I wired lugs 3 and 1 opposite, so lug 3 went to ground, and lug 1 was no connection.

Transistors are socketed.

The issues I have are: gain pot isn't very responsive...there's a difference between all the way up and all the way down, but not a dramatic difference, and change only happens after pot is turned 3/4 of the way.  Also, at full turn, the fuzz seems to slightly cut in and out....no silence..but fuzz intensity cuts in and out.

Q1 (2N3906)
E: 4.14 V
B: 3.44 V
C: 3.06 V

Q2(2N3904)
E: 2.47 V
B: 3.06 V
C: 5.66 V

The battery voltage was 8.66 V

Any help would be awesome.
Thanks

[liddokun]

I can't test the transistors for gain though, I don't have the right equipment.  But could it possibly be a gain issue?

[liddokun]

Does anyone know, or have a link to a page that has the correct gains for this pedal?

[petemoore]

Q1 (2N3906)
E: 4.14 V
B: 3.44 V
C: 3.06 V

Q2(2N3904)
E: 2.47 V
B: 3.06 V
C: 5.66 V
  The emitters stand out as rather high voltage for gain stages, doulbe check the 220*ohm and what resistors near to ground and emitters, orientation of the polarized cap, ground connections, you should read ~220ohm across resistor..to transistor E lead.
  Bases seem high too...but something seems to either be pulling the E's up or not pulling them toward ground enough.

[liddokun]

All polarized caps are oriented correctly, according to the layout and the schematic. I've checked both.  The 220R resistor is good too, and on the schematic it even says to leave it off.  I'm going to try with proper gained transistors, maybe an issue with that.  Everything else seems correct.  Grounds are connected properly too.

[liddokun]

It seems there was an issue with one of the polarized caps connected to the emitter of Q2.  It was oriented correctly, could have a been a bad part.
Once I replaced the cap, the gain pot responded a lot better, and the cutting in and out stopped.  Now I just have to get the correct transistor gains for my
sound preference.