getting a better "sweep" on the fuzz pot

[mordechai]

I just built a fuzz face that sounds terrific once the fuzz pot is turned all the way up, and there's still good fuzz to be found when I turn it down just a little.  But there's virtually no fuzz when I turn the pot down to the 3pm position or less.  Any way to fix this?  q1 is silicon, q2 is a 2n404, the fuzz pot is a 1k, if that helps...

[DavenPaget]

1) Either your pot's a little faulty (i.e 70% disconnected) or the tracks are mostly burnt .
Check with a DMM for your pot . If it shows 0-1K then it's fine . Any smaller pot would make it worse .
That's all i can help .

[alparent]

What schematic did you use? Is your pot linear or Log?

[mordechai]

I used the standard Arbiter fuzz face schematic up on Fuzz Central.  I wonder...would increasing the feedback resistor help? I think the pot is alright and the tracks/traces are strong.

[DavenPaget]

I used the standard Arbiter fuzz face schematic up on Fuzz Central.  I wonder...would increasing the feedback resistor help? I think the pot is alright and the tracks/traces are strong.

I think you should use a parallel resistor to bump the base resistance up . BTW , log or linear as asked by alparent ?

[mordechai]

It's a linear 1k pot.  Can you describe the process of adding the parallel resistor?  Is it just a matter of wiring a resistor between the wire jumper and lug 1?  Would this increase the "minimum" level of the fuzz?

[alparent]

I your log 1 is going to GND the yes, it's just a matter of wiring the resistor between the wire jumper and lug 1
Start with a 330 ohms. Then try other values (470 ohms....)

[liquids]

Smallbear sells 1k reverse log pots for this very reason.

http://www.smallbearelec.com/Detail.bok?no=116

[mordechai]

I will definitely try that.  And thanks for the tip on the reverse log pot...but theoretically, why would this be happening?  I've never quite had this problem before with SO much of the fuzz signal disappearing after turning the pot down past the 80% mark.  is it because I used a smaller feedback resistor this time?  I used an 82K instead of the traditional 100K...maybe this is allow more signal to bleed away back into q1 as opposed to "staying" in the fuzz pot?  But when the fuzz pot is maxed, the signal has more gain and I like it...

[mordechai]

Okay, I put a 470 Ohm resistor on lug 1 of the fuzz pot, and now the entire thing sounds incredeibly choked, virtually nothing coming through no matter how I adjust the pot...

[liquids]

There's been a little bad information here.  If you put a resistor in parallel with the fuzz pot, you are re-biasing the transistor.  

Search around for variants of the fuzz face design.  One solution to this 'problem' that all the range on the fuzz is within a small range is the 1k reverse-log pot, so that the resistance the CAPACITOR sees - say, between none and 100 ohms - takes up more room on the pots travel.

Another solution is to work around this by making spliting up the fuzz pot into it's two roles - as a bias resistor and as a variable resistance between the cap and the emitter.

If you put a 'set' 1k resistor between the emitter and ground, you can THEN re-wire the 1k pot.  

You'd disconnect lug 1 from it's connection to ground and solder it together to lug 2 (or simply leave it connected to nothing).  

Then, strapping a small value resistor in parallel (say, 100 ohms) to the pot between lug 3 and lug 2, with the capacitor connected between lug 2 and ground might be effective in widening the useful sweep of the pot.

But I really think the 1k reverse-log pot is the easiest way to do this...paralleling resistors with pots can be a work around...but it can also yield as unusual a pot sweep as you are experiencing just the same, only different.

[John Lyons]

But I really think the 1k reverse-log pot is the easiest way to do this...
+1
If you have good fuzz with the pot up full and it dies out too fast then the pots taper
is the issue. This is a typical fuzz face issue.

[LucifersTrip]

Another possibility is that even though you think it sounds good, it's still not biased properly.

Do you have ~ 4.5v on Q2's collector?

[Solidhex]

The reverse audio taper pot is definitely the obvious route. Another thing you can do is to basically raise the minimum gain by placing an additional bypass capacitor between the emitter of Q2 and ground. Place something like a 2.2uf there and fine tune the minimum gain with a low value resistor between it and ground. like a 100ohms or so. When the fuzz knob is turned up all the way the additional capacitance won't be as noticeable when combined with the full 22uf you're probably using. It just helps to spread your favorite part of the pot travel across the full range of the pot.

[earthtonesaudio]

I think you should use a parallel resistor to bump the base resistance up . BTW , log or linear as asked by alparent ?

Impedance adds in SERIES, not in parallel.

For adding n parallel resistors,

R_eqivalent = 1/(1/R₁+1/R₂+...+1/R_n)

[DavenPaget]

I think you should use a parallel resistor to bump the base resistance up . BTW , log or linear as asked by alparent ?

Impedance adds in SERIES, not in parallel.

For adding n parallel resistors,

R_eqivalent = 1/(1/R₁+1/R₂+...+1/R_n)

I @#$%ed up . Sorry .

[alparent]

I was talking about a resistor in series with the pot, making it a .5k to 1.5k pot.
I agree a reverse pot would be ideal...I'de even go with a 2k reverse pot.

[mordechai]

What I have found is that when I set the bias to have a "buzzier" sound when the fuzz pot is maxed out, then the fuzz pot has more of a fuzz range as I lower it.  When I set the bias to have a "smoother" sound when the fuzz pot is maxed out, then the downward range on the fuzz pot decreases and anything below, say, 3 o'clock has very little fuzz. 

Does this shed some light on the problem??  Suggestions?  Is it possible that the pot I'm using is just screwy (since I've never had this happen before)?

[LucifersTrip]

What I have found is that when I set the bias to have a "buzzier" sound when the fuzz pot is maxed out, then the fuzz pot has more of a fuzz range as I lower it.  When I set the bias to have a "smoother" sound when the fuzz pot is maxed out, then the downward range on the fuzz pot decreases and anything below, say, 3 o'clock has very little fuzz.  

Does this shed some light on the problem??  Suggestions?  Is it possible that the pot I'm using is just screwy (since I've never had this happen before)?

yeah...it's exactly what I wrote above....the sweep will be better when you have the collector set at ~4.5v
when you alter the bias (ie, the voltage on Q2), the sweep will most likely change

edit: just out of curiosity, how does is clean up with the guitar volume rolled back when you change the bias?

I just did a quick test on a FF sweep with the collector voltage from 3v to 7v. When I set the collector to 7v (more of a distortion) the sweep was very similar to when set at 4.5v (good sweep). When I set to 3v (mushy, more fuzz), the sweep was not as good, with far less change for the first 30-40% of the sweep.

[bwanasonic]

Dunno, it never occurred to me to turn that knob down. That's what your guitar volume knob is for!