Thanks and Fuzz Face questions

[ralley]

Hi all,
  Been lurking here a while and finally got round to registering.  This place is a great resource, thanks a bunch for all the cool information you guys post here.  Great for a beginner like me.

  I've built myself silicon Fuzz Face clone (germanium trannies are next to impossible to get here in South Africa and ordering from overseas can be a nightmare, about to give small bear a try though).  The box is working well but now I want to start fiddling...  I'm using a 470k (cant get 500k) Audio taper pot for volume and 100k Linear for the fuzz (both as per the layout I used) but I'm finding the volume a bit low and the fuzz only seems to have an effect in the last 25% of the pot range.

  I've tried reading up the various articles on pots, lots of info on hacking a linear taper to make it log etc. but can't really find anything on different effects of changing values.  Can anyone recommend new pot values to try to increase the volume and make the fuzz control more sensitive throughout the range?  Also any resources on choosing which value pots to use in general?

Many thanks, Rob.

[newfish]

Hiya!

Which layout are you using?

I'm also fairly new here (and a new convert to the silicon Fuzz Face) - but built one using a 1K pot for the Fuzz and 470K for the Volume.

I may be right in thinking that a smaller value of pot for the volume should even things out a little.
If the signal only really gets going at (for example) 20K or less, the smaller the pot, the sooner you'll reach that value when turning your volume pot.

If you've got spares, there's no harm in changing the pots to something smaller.

Might be easier if you put crocodile clips on the end of your leads (at the pot end) as a temporary measure, then you can change the pots around until you find a value that you're happier with.

Cheers!

Happy tinkering.

[Solidhex]

Yo  Ralley

Are you sure you used a 100k for the fuzz control? The value of the fuzz pot affects the bias of the transistors. 100k is way to much for a fuzz face circuit. The stock value is supposed to be 1k.

--Brad

[ralley]

Whoops, my mistake I meant I use a 1K Audio taper pot for volume.  The layout is the DragonFly one from the gallery here.

Rob.

[petemoore]

Whoops, my mistake I meant I use a 1K Audio taper pot for volume.  The layout is the DragonFly one from the gallery here.

Rob.

1k is very small resistance to have between signal path and ground and will shunt 'a lot' of signal, reducing output, 20k is still 'small', 100k is most common, 500k works [~like 100k if you taper it down].
  But the Fuzz/gain pot wafer value matters a lot because it sets gain in the circuit, you can use a fixed resistor instead of a pot [see Sili Face IIRC, ROG has a FF with Fixed gain R.
  Which is pretty cool, I actually prefer a fixed resistor replacing the gain pot, and input pre-gain instead in some ways, main thing is it won't work right without something between say 820 ohm and 2k as Fuzz resistance [where the potwafer is connected in 'regular' FF].
  But we're into variations on a theme, it is recommended to refer to applicable schematic for sorting into language: what exactly is where, what it does 'if' etc.
  IOW first order of Bs would be get ~1k across where the gain pot is shown, get the circuit fired up and biased..see if you can find a schematic which represents closely what you have there on the board.

[Dragonfly]

Whoops, my mistake I meant I use a 1K Audio taper pot for volume.  The layout is the DragonFly one from the gallery here.

Rob.

I think you mean "1K for Fuzz control".

Linear taper is best. Audio taper will "bunch up" at the end, like you mentioned.

Master volume calls for a 500k audio taper pot...though depending on the FF configuration, I use 100k's quite a bit.

[ralley]

Phew, sorry about that, kept getting the values mixed.  What I really used was a 470k Log pot for volume and a 1k Linear pot for Fuzz. 

Dragonfly - I see your layout lists a log pot for the fuzz control, is that a mistake? (The schematics at Jack Ormans site and my intuition said to use a linear here).  I used a linear pot but the behavior of the fuzz control seems log like, "bunched at the end" as you put it.  I'm going to check the pot and make sure it is not just mis labeled. 

If I change the volume pot from the 470k to a lower value will that have the effect of making the control more sensitive (due to smaller resistance range in the same physical, trun, range) but not enable me to turn the volume down as far? (Lower maximum resistance, eg. 250k vs. 470k).  Would it have any affect on the maximum volume?

Rob.

[petemoore]

  Small Bear stocks the 'Fuzz Face' gain pot, specail taper 1k pot makes dialing in gain very even.
 

[shredgd]

Phew, sorry about that, kept getting the values mixed.  What I really used was a 470k Log pot for volume and a 1k Linear pot for Fuzz. 

Dragonfly - I see your layout lists a log pot for the fuzz control, is that a mistake? (The schematics at Jack Ormans site and my intuition said to use a linear here).  I used a linear pot but the behavior of the fuzz control seems log like, "bunched at the end" as you put it.  I'm going to check the pot and make sure it is not just mis labeled. 

If I change the volume pot from the 470k to a lower value will that have the effect of making the control more sensitive (due to smaller resistance range in the same physical, trun, range) but not enable me to turn the volume down as far? (Lower maximum resistance, eg. 250k vs. 470k).  Would it have any affect on the maximum volume?

Rob.

The fact that the available gain is all crowded at the end of the fuzz pot in a FF is normal, that's why someone sells a special taper pot (actually a reverse log, I think) for that. Generally few people care, because FFs are usually used with the fuzz pot all maxed out!.. That's also why someone uses a fixed 1k resistor instead of a pot there.
If you really need to dial in the gain more precisely, you can do without the special pot by using a normal log pot wired backwards: this way you have the same behaviour of a reverse log pot, except that the pot works backwards., i.e. with gain increasing when the pot is turned counter-clockwise instead of clockwise.

About the vol pot: newfish said it wrong, if you lower the value of the pot you won't get the maximum volume available sooner, because you'll shunt more signal to ground, actually giving you less volume. What he meant is probably that you could use a lower value pot + a fixed resistor between the pot and ground; but this will set a minimum volume under which you cannot go.
Is the volume of your pedal too low even with the vol pot at max? In this case I think you have to check your circuit again. Otherwise, if you just want your pot to be at 8 o'clock for unity volume, and you want to have the other 7/8 of turn for brutal volume boost, you're probably simply asking the pedal too much... 

Giulio

[newfish]

mea culpa...

[nooneknows]

Is the volume of your pedal too low even with the vol pot at max? In this case I think you have to check your circuit again. Otherwise, if you just want your pot to be at 8 o'clock for unity volume

To increase the volume there's always the chance to modify the balance of two resistor values on the 2nd tranny collector, increasing the R closer to the supply voltage should give more headroom.