Fuzz Face Problems

[oucivileng]

I recently got my first pedal working and it sounds fantastic in general, however it has a few small problems that I was hoping
someone could help me with.  Since it was my first pedal, I went for the simple but classic Fuzz Face.  Instead of germanium transistors, I
bought some silicon ones to use until I get all the problems worked out so I wouldn't have to worry about burning up a part that would be difficult to replace.  Unfortunately, I accidentally bought transistors with an hFE of 250.  This is definitely higher than I wanted.  I think I just clicked the wrong "add to cart" button on the Mouser website or something.  I'm thinking this might be the source of all my issues but I wonder if I can solve this problem with a resistor or two someplace.  Here are the problems I'm having:
1. The pedal is way too loud; the volume difference between "on" and "off" is so great that I can't even compensate with the volume knob on my guitar
2. When I turn the volume all the way down on my guitar, the pedal makes
a loud, steady, monotone noise
3. When I turn the fuzz knob almost all of the way up, it starts making this painful high-pitched noise although I can still play through it.

Please help!

I'm using the negative ground schematic from the Tonepad website

[John Lyons]

I think you have the volume know wired incorrectly.
The transistors do not affect the volume per se.
This may also be the problem with the squeal/oscillation.
Recheck that the volume pot is wired correctly.

john

[oucivileng]

Thanks for the reply, John.  You were right about the volume knob, and that fixed the problem with it being too loud, however the other two problems remain.  Any other ideas?

[petemoore]

  The FF can be very high gain, much higher than is needed to cause self-oscillation.
  See GEO Technology of the Fuzzface, and other FF resources to understand better how to tame a FF to do more what you want, lower the gain compliment from the transistors maybe, 250hfe is up there.
 

[darron]

the monotone noise is a very common issue with the fuzz face layout. it can be ind of fun to roll back your volume knob almost all the way then change the pitch by rolling it in slightly (:
the transistors begin to self oscillate. that's a massive problem for most people who build a PNP version with a negative ground.

are you powering it off a power supply or battery?

the generic quick fix for the issue is to usually slap a massive electrolytic capacitor across the power rails as close to the circuit as possible (IE, not on the power supply half a meter away). so a 1000uF or 470uF or something on positive input and ground on the board might help out with the problem. filtering will often help with the motorboating, and sometimes the high pitch squeels when you set the gain higher, but squeeling isn't normally something i'd associate with a FF, but can happen with any circuit with enough gain.

[oucivileng]

I'm currently only using a battery.  I'll probably upgrade to a power supply in the near future and that will probably create a whole new set of problems.  I chose to try the pnp with negative ground first because I'm worried that hooking up both positive grounded pedals and negative ground pedals in series would be problematic.  Doing so would cause the negative wire from one pedal's power to be directly connected to the positive wire of another via the cable connecting them to each other.  Is this correct?  Is this a legitimate concern?  I might just scrap the whole design and rebuild it with NPN and a negative ground if I can't get it working the way I want.  It's not like it takes a long time to reassemble or costs a lot.  Any thoughts?

[John Lyons]

A ha!
Yes, this most likely is the problem.
Put in some NPN with a negative ground
or keep the PNP and use a positive ground.
If you are using a battery only there is no problem
using PNP/pos ground pedals with a power supply.
The problem is when you use a power supply and
mix neg/pos power.

Make sure to orient all caps and diodes for either
neg/pos ground.

John

[snarblinge]

dude the squealing just means its working, check out Jimis Radio 1 promo for some classic Fuzz face goodness, thats a selling feature.

[oucivileng]

I was playing around with my pedal a bit ago and I figured out what the so called "squealing" noise is.  It's radio interference.  Here's how I figured it out: I turned the fuzz knob up to about 85% where it starts making the high pitched noises and squeals. Then, I started playing with the volume knob a bit and suddenly I hear a faint voice coming through my amp telling me something about jesus.  One of the local christian radio stations must broadcast on a frequency that's close to the circuit's resonant freq or something.  I think I'm going to try some transistors with lower gain tomorrow, if that doesn't sound better, I'll rebuild.  Thanks for the help, everybody.  Have a good weekend

[darron]

god is on the radio. haha, that's great (:

you are right in thinking that positive and negative grounds will clash, but that would only be the case if you were using a common power supply. IE daisy chain. If you are using an isolated supply such as a battery or another transformer then you shouldn't have problems.

most people will tell you to never use PNP with negative ground, but i never find any problems when you keep to good design guides. if you didn't have an LED you could run it with a positive ground for AGES without needing to change the battery, but i hate batteries.



finding radio stations isn't uncommon. i had a wah that could tune them in

there are a couple of things you could try to help out with that. use a metal enclosure and earth it. try sticking a 220pf capacitor on the input to ground to help filter radio frequencies out.


the monotone noise is called motorboating by the way, and you' often get it when you turn the fuzz/gain knob up too with negative ground. the 1000uf capacitor should fix that though.