Fuzz Face Hiss when maxed?

[carboncomp]

Iv just built a silicone Fuzz Face clone and it sound amazing until I turn the fuzz knob to max, then there is a huge leap in Hiss and noise (but only in the lest fraction, 9 to 10).....is this just the way fuzz faces are? and is there a way to resolve it? 

[LucifersTrip]

I've had the same problem with a few of the FF -type fuzzes.  A small cap 200-300pf in strategic locations will many times solve the problem,
hopefully without changing the tone you already have.

In this case [link below] a cap across the collector & base of Q1 solved the problem.  I'm sure other forum members will be able to tell you other possible cap positions to try. If I remember correctly, I solved another wail problem on a different pedal with a cap across the two bases.

Here's the old post where I asked the exact same question.
http://www.diystompboxes.com/smfforum/index.php?topic=87501

good luck

[newfish]

I've had the same problem with a few of the FF -type fuzzes.  A small cap 200-300pf in strategic locations will many times solve the problem,
hopefully without changing the tone you already have.

In this case [link below] a cap across the collector & base of Q1 solved the problem.  I'm sure other forum members will be able to tell you other possible cap positions to try. If I remember correctly, I solved another wail problem on a different pedal with a cap across the two bases.

Here's the old post where I asked the exact same question.
http://www.diystompboxes.com/smfforum/index.php?topic=87501

good luck

+1.

I have a tiny cap (47pF or so) across the two output lugs of my FF volume pot.
Shaves off most of the hiss (I like a little bit for added Mojo), and knocks off any Radio Stations trying to upsset my vibe.

[nocentelli]

Output lugs?

Or outside lugs? 

[petemoore]

 FF volume pot is assigned as an adjustable resistive divider, the wiper is like a mixer for AC signal and DC ground to create output level control.
 
  Gain pot is FF gainpot taper [ask Steve @Smallbear].
  Other tapers will have >50% of the gain-sweep in the last 5% of their rotational range, this makes the fuzz-gain jump on at the last bit of knob twist.
  It can make it rather difficult to control the gain setting.
  A fiddled with then fixed preset circuit gain, and adjustable input pre-gain can be easier to cobble together.
  Depending on the pu output level: Set a fixed value of 1k or so, substituting the gainpot [to taste], with the guitar set to almost 10 and 10...'high gain' but not super hiss-swamp fuzz [or a double not on curtail the gain, but hiss, mud and/or then oscillation are behaviours associated with exceeding  'the reasonable gain ceiling parameter'.
  Another option was cobble in a <500ohm pot + a fixed stop resistor to add when ATWup to about 1k, something like 200ohm pot + 800ohms fixed-stop resistor. Smaller gain range starts nearish full gain and the pot then has between there and full gain so hopefully that or 1 more tweek makes it at least possible to more gradually control what is usually a 'small window'.
  1000 ways to set up a FF, and then the guitar volume 'can' be the gain knob, essentially a pre-gain knob is another VC parallel to the guitar VC.
  If boiled right, a volume knob is all that ends up being used, presetting the circuit gain R, using a touch of input attenuation to mimic guitar volume at say 'around 9+?'...some sweetening may occur just below 10 on the Guitar volume, the value chosen for 'less than swamp-fuzz' [measured R across the guitar volume pot Input/Output signal lugs] is a good value to start with for fixed R at input [ie to mimic, and more accurately preset the slight clear up/still HG fuzz sound, that X guitar gets when VC is set to 9.6473 setting], then when slamming the guitar volume ATW to 10, it's actually 9+? as far as the FF is concerned, set that value carefully.
  Then..looking at the guitar pot very carefully, HP bleed cap across large value guitar VC pot signal lugs ? [allows some treble to bypass the pot when turned dow to...where the resistance for HF's is less through the bleedby-cap than the large resistance created as guitar volume is turned down.

[newfish]

Outside.  Outside lugs.

The two lugs at each side of the volume control.

Not the wiper.

<my fingers are already in weekend mode>

[newfish]

Also, GEOFX's 'Technology of the Fuzz Face' article is well worth a look.

The 'Fuller' mod is worth a look (a 47K pot in series with your input signal) - effectively allowing you to control the amount of signal hitting the FF.
Using this in place of a 'traditional' Gain / Fuzz control is, for me, the way forwards.

The 'trad' Gain / Fuzz pot gets replaced with a low value resistor (say 10 Ohms or so) - so there's always plenty of dirt on-tap without oscillation.

The 'Fuller' input control also, to my ears, helps preserve the treble at all settings, as the FF is at its 'let everything through' setting for 'Gain / Fuzz'.

You could always leave the stock FF at full gain and roll back your guitar's volume control.  This was good enough for Jimi...

[newfish]

Minor bump...

Made a deliberately hissy FF on my Breadboard over the weekend.

Adding a small (200pF / 470pF) cap between the Base and Collector of Q1 is definately the way to go for removing hiss - without adversely affecting the 'bloom', 'warmth' etc...

Nice one, Lucifer's Trip!

Having a lucky find of an Si NPN with an Hfe reading of '67' also made my weekend... 

[John Lyons]

Adding a small (200pF / 470pF) cap between the Base and Collector of Q1 is definately the way to go for removing hiss - without adversely affecting the 'bloom', 'warmth' etc...


+1

[R.G.]

N.B.
The "hiss" you hear suddenly jump is the pedal going into ultrasonic or RF oscillation. The jitter and/or phase noise of the oscillation is rectified by the semiconductor junctions and detected as audio, which you hear because of the large gain.

Small signal silicon transistors generally have good gain up to 100MHz or so; it's easy to make an unintended RF oscillator if your layout, decoupling, and wiring are not great. Stopping this nonsense generally involves a low-ESR ceramic cap of about 0.001 to 0.1 across the power supply, and a collector-base cap on one of the transistors, usually Q1, to lower the gain above the audio region. 30 to 4700pF is generally enough. Hard cases may need a 1K "base stopper" resistor right at the base of one of the transistors to add some dissipation; otherwise, some situations can turn this into a decent AM band radio pickup, as the feedback cap can tune in a station with the inductance of the wiring. The resistor damps the resonant peak that helps this happen.

[carboncomp]

Thanks for all the tips!

It took a 1nF across the Q1 to get rid of all the hiss and random feedback gain rolling thunder noise.

[thetragichero]

i get a spanish talk radio station with the gain on my fuzz face maxed at my house
i like it, adds a bit of lofi mojo!