fuzz face help

[jg24]

Hi, new on here and to building my own pedals... realising how addictive it can be!  Have put together a couple of BYOC kits and am now working on a pnp fuzz face from musikding - this one:

http://diy.musikding.de/images/stories/face69er/face69wire.pdf

I don't want to include the power jack - I just want to run it from a battery.  So the question I have is, as well as leaving out the power jack, can I leave off the diode and the 100uf cap and replace them with jumper wires?  From what I've read about the many fuzz face circuits out there these two components are only necessary if you run the pedal from the mains - is that right?

Any help would be appreciated!

Edit - Realise I should probably have linked to this diagram instead of the other!:
http://diy.musikding.de/images/stories/face69er/69erschalt.pdf

[anchovie]

Yes, go ahead. Those parts weren't in the original Fuzz Face anyway.

[jg24]

Cheers James - appreciate the reply.

[G]

So the question I have is, as well as leaving out the power jack, can I leave off the diode and the 100uf cap and replace them with jumper wires?

Leave off the diode and cap, but don't replace them with jumper wires.  If you do that, you'll short circuit the battery and it'll get very hot very quickly.

Just leave the holes empty and it'll work fine.

[BAARON]

No, leave the diode in there.  It's to protect the circuit in case you accidentally touch the battery to the clip backwards.

You can lose the cap though.  But as G said, don't jumper it: just leave it out.

[petemoore]

  The 4001's nice for reverse battery abuse, it hopes to prevent reverse polarization damage.
  C4 would be useful for reduction of ripple from a power supply, of no benefit with battery use.
   

[jg24]

Many thanks for the replies and info!  That's great.    As is obvious I've no idea what goes on in the circuits... and really need to go read a book on the basics!

[BAARON]

If you have the filter cap in place, it's going to change the way the circuit sees the battery.  A fresh battery has almost no AC impedance.  A dying battery starts to build some up.  That's part of why a Fuzz Face sounds different with a fresh vs dying battery.  If you put a big filter cap in place, it effectively reduces the AC impedance of the battery to zero, so the circuit will always be seeing what it thinks is a fresh battery and you won't ever get that "dying battery" mojo.

However, if you put something like a ~300 ohm resistor between the filter cap and the rest of the circuit, it will permanently see about 300 ohms impedance from the power supply, whether it be a battery or adaptor.  The filter cap will take care of adaptor hum, and the ~300 ohm resistor will make the power supply look like the rising impedance of a dying battery.  This means you'll get something akin to the "dying battery sound" all the time, regardless of the voltage level of the power source.  (In case you're wondering, the dying battery sound is a good thing with a Fuzz Face.)

So in addition to the basic Fuzz Face circuit, you could have a:
- diode going from ground to your power supply, with the cathode pointing toward the + side of the supply, in case a battery is ever put in backward or an adapter with the wrong polarity is used
- big capacitor (100-220µF) going from your power supply to ground, oriented with the negative lead going to the negative/ground side of the power supply (obviously) to help smooth out hum from bad wall warts
- ~300 ohm resistor attached to the power supply, off of which the rest of the fuzz face circuit gets its power (so the entire circuit, aside from the diode and filter cap, draws its power THROUGH the resistor) to emulate "dying battery impedance"

Disclaimer: I'm not entirely sure what the AC impedance of a dying battery is when it's in its "sweet zone" for a fuzz face, but I think it's supposed to be about 300 ohms.  I could swear I read that somewhere, but when I went to cite the original article one day, I couldn't find the figure.  So 300 ohms could be wrong, but it's a starting point to experiment with.  If anybody knows the AC impedance of a dying battery, I'd love to find out what it is.

[jg24]

Thanks for explaining things Aaron - that's very helpful.  I'd picked up about the effect a dying battery can have in a fuzz face (I've not actually used one yet, but gather it gives you more/better fuzz?).

As I'll just be running the pedal from a battery I'll leave out the fliter cap, but keep the diode.  The 300ohm resistor mod to emulate the dying battery sounds very interesting.  But perhaps an easier dying battery mod to include in the circuit (as I'm using a pcb) is this one I've seen at Beavis Audio.  What do you think?  I guess it might be more useful if using a battery (the power of this diminishing over time)?

http://www.beavisaudio.com/Projects/FuzzLab/FuzzCloneMods_V2.gif

Thanks again

[BAARON]

The only difference between using a 300 ohm resistor and a 100k pot is that the pot is adjustable and can provide waaaay more sag than the 300 ohm resistor will - i.e., you can limit the current so much that the pedal won't even work.  The 300 ohm resistor is a lot more subtle, but you'll notice that it's there if the rest of your circuit is a stock Fuzz Face.  It's the same principle in the same spot on the circuit though.

HOWEVER I just looked at the schematic for what you're doing and realized that it's positive-ground, which might not play nicely with your other effects.  You might want to read this: http://www.muzique.com/lab/fuzzface.htm

AND THEN I realized that your indicator LED is running off the same power traces on the PCB as everything else, so if you put a 100k pot between the battery and your circuit, you'll also be limiting the power to the LED, which may or may not be a good thing.  (I'm guessing it will not be a good thing.)  It may take some off-board wiring to do this well.  The LED and its current limiting resistor will probably have to get power right off the battery clip/power jack instead of off the power trace on the board, if the power on the board is going through a resistor or pot to induce some battery sag.

[jg24]

Ok - thanks for the advice.

It's because the circuit is pnp I decided to leave out the power jack and just stick to batteries (like the original fuzz face).

I guess placing a 300ohm resistor or 100k pot in front of the LED wouldn't cause it any damage - but would just dim it or turn it off as you reduce the power?  But from looking at the schematic don't presume it would be difficult to wire the LED in front of the pot - just running a wire from the negative battery lead (it being a pnp circuit) and fitting R6 (1.5k) to this wire instead of to the pcb and then to the LED??

[BAARON]

Exactly.  Just run a resistor between the battery clip and the LED and leave the board out of the LED circuit entirely.

If the resistor/pot were in front of the LED and the circuit, you'd be limiting the current to both.  The LED would probably stop lighting up pretty early on the 100k pot's sweep, and it may or may not change the way the circuit behaves as you limit the current more and more (because they both end up drawing their current from a very low-current source (the 100k pot, which won't let much through once it's turned up) instead of from a high current source (the battery)) as compared to if it weren't there.

[jg24]

Great - thanks for the help!

I will prob go for a smaller pot than 100k as it seems a bit excessive - the Beavis Audio mods page says you can use a 50k instead.  I think I'll go for that (although from a search on here I see that 10k seems to be the norm for a starve/sag pot).

Thanks again!

[zombiwoof]

I've always thought the reason that players liked a dying battery in the FF is because of the treble rolloff that you happens when you turn the volume control down (similar to what happens on many guitars).  If the battery is dying, you'd have to turn the volume up higher to compensate, and there would be less treble rolloff present.  I was looking at a schematic of Roger Mayer's Classic Fuzz and it appears that he puts a small cap across the volume control, which would be a treble bypass thing similar to what is used on guitars to control the treble rolloff, and I have done that on my modified FF.  It does help to keep the treble as you turn down the volume pot.  I could be wrong about the dying battery theory I have, but the treble bypass cap does help the sound on my FF.

Al

[BAARON]

As the battery dies in a fuzz face, the added battery impedance combines in series with the tiny 330/470 ohm resistor between your power source and the output cap.  Noticing that the 330R resistor in combination with the 8k2 resistor forms a voltage divider that throws away most of the signal, increasing the impedance of the 330R resistor (which happens as the battery starts to die) actually shifts the middle point of that voltage divider and gives you More output power.  That's one of the reasons a common FF mod is to replace that 330R with something like 1k5.

RG's article about the FF is a good thing to read.