Fuzz question.

[Bluesman]

I'm planning to build a Dallas Arbiter fuzz with a few extra features, i would like to have a trimpot on the pcb that i can use the same way as the volume knob on the guitar.  I'm not sure if the right way to achive that is to make it the same way as the bias knob on the boutique fuzz at GGG (link to the schematic below) but i guess that it's the way to do it or?.
I guess that the 1M resistor that is connected between the input and the 50k biaspot and to ground is something that i need to have there to?.

http://www.generalguitargadgets.com/diagrams/fuzzface_b_sc_pn.gif

Bluesman.

[Bluesman]

Anyone who can help me?.

Bluesman.

[bioroids]

I don't think that schem is exactly what you need.

Check out this:

http://sounds.ampage.org/files/NITRONOMETER.gif

You want the "fuel" pot. I'd add too the tone pot and make them at the top of the box, instead of trimpots.

Luck

Miguel

[trevize]

the ggg boutique ff project  is the fulltone 69.
i tryed it and i think that probably it was the most useless pot on that pedal.
after building a lot of fuzz faces the only mod
to the original circuit i would keep it's the contour pot.

[Roobin]

So you want a trimpot before the main circuit, to control input level?
What are hoping to achieve? To control the point at which 'fuzz' starts?

[petemoore]

  I Use that 250k pregain pot wired like volume *control, a good thing to have.
    It works great for presetting my HB's to a less saturated 'max volume' on guitar, so that I can hit '10' on the guitar volume and have that be like '8.572', or...just under 'oversaturation' which can be muddier than what I'd want on the low strings in particular, that point on my guitars volume control takes re-targetting time to find, hitting that spot once with the pregain allows me to hit the 10 stop of my guitar volume pot and have it be right where I like the tone.
 
 

 

[WGTP]

I like the pre-gain pot because it varies the input impedance and reduces the bass and woofiness.   

[Bluesman]

  I Use that 250k pregain pot wired like volume *control, a good thing to have.
    It works great for presetting my HB's to a less saturated 'max volume' on guitar, so that I can hit '10' on the guitar volume and have that be like '8.572', or...just under 'oversaturation' which can be muddier than what I'd want on the low strings in particular, that point on my guitars volume control takes re-targetting time to find, hitting that spot once with the pregain allows me to hit the 10 stop of my guitar volume pot and have it be right where I like the tone.
 
 

 

Yes that is exactly what i want, so 250k is a good value for that pot?. I think that i made it moore difficult than it is to implement a pot like that to the fuzz circuit, if i just put in a pot at the input (no resistor to ground like the bias pot on the boutique fuzz) of the circuit i guess that vill act the same as the volume pot on the guitar?. I think i skip the first plan to have that pot inside as a trimpot and put it outside instead, could be handy to have it there if i would like to use the fuzz without any resistance on the input.

Bluesman.

[petemoore]

  If you have place for the pot, it can be as easy as splice it in as a Variable resistor in the wire from the switch to the circuit input. 50k seems to be the recommended value.
  I just used a 250k wired as volume pot, and like the way the knobs work on the box...of course it's a 3 transistor Boost/Fuzz Thing...I think I saw a wiring like that somewhere...
  Anyway there are a variety of ways to control the gain of a FF, and input gain control...with carefully chosen fixed circuit gain control...for somebody willing to set it up right and wants 'this' knob to do 'that'...I sezz it can be a close running as to percieving which is the more versatile/usable second knob to have on a FF.

[Bluesman]

  If you have place for the pot, it can be as easy as splice it in as a Variable resistor in the wire from the switch to the circuit input. 50k seems to be the recommended value.
  I just used a 250k wired as volume pot, and like the way the knobs work on the box...of course it's a 3 transistor Boost/Fuzz Thing...I think I saw a wiring like that somewhere...
  Anyway there are a variety of ways to control the gain of a FF, and input gain control...with carefully chosen fixed circuit gain control...for somebody willing to set it up right and wants 'this' knob to do 'that'...I sezz it can be a close running as to percieving which is the more versatile/usable second knob to have on a FF.

Ok, my english is not so good so i need to check that i understand you right , when you say spliced in as a variable resistor i guess you meen that i use only two lugs on the pot (the one in the middle and one of the side lugs) and splice it in on the circuit input  and for that type of arrangement the recommended value on the pot is 50k.
Wired like a volume pot i use a 250k pot and connect the third lug on the pot to ground.
Witch one of these to alternatives is the one that is closest to get the same effekt as if i roll of the volume on the guitar?.

Bluesman.

[petemoore]

  Ok...say you have a 250k volume pot on your guitar wired the exact same way as a 250k 'pregain' [and in exactly the same position in the chain, except for the guitar cord], turning either of these up/down...does the same thing...roll off gain at the input...a great way to see if you'd like the 250k input gain mod is to turn your guitar volume down.
  The 50k variable resistor method...just inserts 'x' amount of resistance [between 0k and ~50k] to the signal before input to FF, which also rolls off gain, doesn't go to '0' volume, and is probably usable over it's entire range/and provides 'finer' adjustment...very similar to turning the guitar down...if you have 500k pots in the guitar, you could roll it back to 450k/50k [which probably occurs at about 9 on the dial]...whoops...audio pot...any rate, there wouldn't be loading to ground much through a 400k resistance...
  Basically either one'll work...try 'em both...I'm sure they're also just a little different.

[Bluesman]

  Ok...say you have a 250k volume pot on your guitar wired the exact same way as a 250k 'pregain' [and in exactly the same position in the chain, except for the guitar cord], turning either of these up/down...does the same thing...roll off gain at the input...a great way to see if you'd like the 250k input gain mod is to turn your guitar volume down.
  The 50k variable resistor method...just inserts 'x' amount of resistance [between 0k and ~50k] to the signal before input to FF, which also rolls off gain, doesn't go to '0' volume, and is probably usable over it's entire range/and provides 'finer' adjustment...very similar to turning the guitar down...if you have 500k pots in the guitar, you could roll it back to 450k/50k [which probably occurs at about 9 on the dial]...whoops...audio pot...any rate, there wouldn't be loading to ground much through a 400k resistance...
  Basically either one'll work...try 'em both...I'm sure they're also just a little different.

A few days ago i looked at the shematic for my stratocaster and discovered that the volume control on the guitar was wired the same way as the pregainpot in the Easyface shematic (but after the guitarcord as you said) and i decided to do the same arrangement on the fuzz i'm going to build.
Then i found som close pictures of the sunface pcb somewere here on the forum and found out that it probably was wired something like the 50k mod you describe, at last i looked at the 69 schematic and discovered another wiring on the so called biaspot on that shematic.
I was getting a little confused about what would be the right mod for me so thank you so much for your feedback on my questions it has helped me alot. Since i decided to put the pot outside instead of a trimpot on the pcb it's much easier to try both the 50k and the 250k mods, with the trimpot on the pcb i would have to decide witch mod to use when i make the pcb layout.

Bluesman.

[petemoore]

  You could, and I have, gone 500k there, and that's cool, but turn it downmuch and your'e getting to around 100k series signal path resistance, and that rolls off highs more, which too, can be cool.
  A fix for highs is a little cap [some kinda 100pf or whatever...yer gonna need sample values anyway...just start with something and work with it...anyway, a cap across the pot's lugs that recieve and output the signal...then when turning down the pot the highs are retained, a different kinda treble boost [with a little bit bigger cap on the pot] can also be tried...
  Anything under 250k [I arbitrarily chose that number...cause 100k is the next smaller EZ avialable value]...anyway smaller-ish resistors from signal path to ground can start loading the signal, and the pot wafers value [which is connected to lugs 1 and 3 of the pot...] is no exception.

[Bluesman]

  You could, and I have, gone 500k there, and that's cool, but turn it downmuch and your'e getting to around 100k series signal path resistance, and that rolls off highs more, which too, can be cool.
  A fix for highs is a little cap [some kinda 100pf or whatever...yer gonna need sample values anyway...just start with something and work with it...anyway, a cap across the pot's lugs that recieve and output the signal...then when turning down the pot the highs are retained, a different kinda treble boost [with a little bit bigger cap on the pot] can also be tried...
  Anything under 250k [I arbitrarily chose that number...cause 100k is the next smaller EZ avialable value]...anyway smaller-ish resistors from signal path to ground can start loading the signal, and the pot wafers value [which is connected to lugs 1 and 3 of the pot...] is no exception.

Ok, i have a lot of both pots and capacitors of different values that i can experiment with as soon as i got the fuzz finished, i have the pcb layout almost ready so i guess there will be a etched an drilled pcb ready to solder sometime at the beginning of next week.
I'm also planning to put a dial knob on the outside in the same way as on the sunface so i can adjust the voltage at collector of Q2, seems like a good idea to have when using tempeture sensitive Ge transistors.

 
Bluesman.

[petemoore]

Bias dial is a good one, I find bias fun to set on top of a box for a while, I took some readings from time to time and noted the position of the knob marker...actually the sweet spot on that knob didn't move much, but it did afford the ability to fine tune bias when in use...that helped me get an idea of what a little lower voltage or a little higher voltage from 1/2v sounds like...for that one...and another one might drift more...I know I had one with driftage on the bias...
  anyway, I'm finding 4k7-5k6 are good values to series with a 10k linear pot, this can dial close to or past misbias [some gating at full CCw or Cw] without having the knob be able to shut off the circuit completely. so the range worked out well for having enough' variance of resistance [that'd be 4k7 - 14k7 adjustable with a {4k7 + 10k pot} and fine tuning with no complete shutoff available.

[Bluesman]

Bias dial is a good one, I find bias fun to set on top of a box for a while, I took some readings from time to time and noted the position of the knob marker...actually the sweet spot on that knob didn't move much, but it did afford the ability to fine tune bias when in use...that helped me get an idea of what a little lower voltage or a little higher voltage from 1/2v sounds like...for that one...and another one might drift more...I know I had one with driftage on the bias...
  anyway, I'm finding 4k7-5k6 are good values to series with a 10k linear pot, this can dial close to or past misbias [some gating at full CCw or Cw] without having the knob be able to shut off the circuit completely. so the range worked out well for having enough' variance of resistance [that'd be 4k7 - 14k7 adjustable with a {4k7 + 10k pot} and fine tuning with no complete shutoff available.

Thanks for the advice on what values to use for the pot and resistor, good to have people that is willing share their knowlege and experience.

Bluesman.