A Simple Fuzz question

[italianguy63]

But it seems nothing is ever simple.

On a basic Fuzz Face, the Fuzz Pot is 1K Linear.

What would be the effect if it was swapped for a 5K Linear.  Would it create ill effects or just reduced sensitivity??

MC

[GGBB]

No ill effects, but would allow for lower gain / less fuzz settings, but not significantly.  Most of the variation occurs close to zero ohms - max fuzz is when the pot is dialed down to zero ohms - and for that reason a 1K reverse audio pot is recommended rather than linear.  With 5K you'd have 5x less precision/control over the usable portion.  Unless you find that a 1K pot doesn't allow you to lower the fuzz enough, stick with the 1K.

[italianguy63]

Thanks-- what I figured, but wanted to be sure....

[nocentelli]

Wouldn't a 5k pot totally mess with the bias of Q2?

[Mark Hammer]

Depends how you use it.

The AC gain will be a function of the resistance from the emitter to a suitable-value cap to ground.  Lower impedance path = higher gain.  The "classic" FF wires up the pot to do double duty, as both a fixed resistance to ground from the emitter, and a variable emitter-to-cap resistance.  As you move the wiper around, the emitter-to-ground resistance remains the same, but the resistance from emitter to cap changes.  Clever.

But take a look at the AMZ MosFet Booster below.  A person could simply stick in a fixed 1k resistor in place of the standard 1k pot, and simply connect the  5k pot to the ground cap.  In other words, instead of combining the two functions into the one pot, as the FF does, simply separate the two functions, such that a fixed resistor handles the biasing, and a variable resistance handles the gain.  Actually, the nice thing about doing that is that one can monkey around with various parallel fixed resistances to transform the taper of a 5k (or even higher-value) pot to whatever you like.  (Note that it doesn't matter if the pot "comes before" the cap, or vice versa)

[nocentelli]

I assumed from the original question we were talking about a straight swap.

There seems little point in adding a 5k variable resistor pot for the cap in parallel with the emitter resistor if the emitter resistor is left as 1k: Once the 5k pot resistance is dialled above 1k, there will be no further audible reduction in gain/fuzz.

[italianguy63]

Yeah--

But I can get a clear shart 5K pot.  They don't make a 1K one!   

[nocentelli]

If you use the 5k pot as a variable resistor with the cap in parallel with a fixed 1k off the emitter, you won't get much increase in fuzz until turned up way beyond half-way. Also, the critical last couple of hundred ohms of resistance will be bunched up into a space a fifth of the size of the original 1k pot.

Actually, the nice thing about doing that is that one can monkey around with various parallel fixed resistances to transform the taper of a 5k (or even higher-value) pot to whatever you like.

This is a better idea: A 1k2 in parallel with the 5k-as-variable-resistor would give you a roughly 1k reverse log pot.

[italianguy63]

Hey thanks!  That's helpful!!

[Davelectro]

A 1k2 in parallel with the 5k-as-variable-resistor would give you a roughly 1k reverse log pot.

IIRC it's not that easy. I tried that trick in a Colorsound Overdriver (50K pot // 12K resistor to fake the recommended 10K-C) and I could never get an antilog response. As far as I remember the control kept acting like a regular 10K linear pot.

In my opinion, reducing the pot value works better than faking a reverse taper.

[nocentelli]

It was just a suggestion so he could get something useful out of a 5k clear-shaft pot. I tend to use 1 k linear for a fuzzface without much difficulty.

[JustinFun]

My 2 cents - I've always found the fuzz control on a fuzz face to be useless except when maxed anyway - I tend to hard wire it open and then use a 'pre-gain' (variable series resistance on input, 100k pot) which gives great variation from vintage overdrive to all-out fuzz madness. Just my opinion, but I can't see any use for that control once you've tried the pre-gain mod.

[GGBB]

A 1k2 in parallel with the 5k-as-variable-resistor would give you a roughly 1k reverse log pot.

IIRC it's not that easy. I tried that trick in a Colorsound Overdriver (50K pot // 12K resistor to fake the recommended 10K-C) and I could never get an antilog response. As far as I remember the control kept acting like a regular 10K linear pot.

Faking a reverse log taper only works when the pot is used as a variable resistor to increase resistance clockwise (between lugs 1 & 2).  When set up to decrease resistance (between lugs 2 & 3) as in the Colorsound, the technique fakes a log taper instead.

[induction]

Faking a reverse log taper only works when the pot is used as a variable resistor to increase resistance clockwise (between lugs 1 & 2).  When set up to decrease resistance (between lugs 2 & 3) as in the Colorsound, the technique fakes a log taper instead.

Exactly. I believe this is what R.G. meant in 'The Secret Life of Pots' with the statement near the end:

You can't simply put the tapering resistor from the CW terminal to the wiper and get a log taper pot emulation, like you could with the voltage divider connection. That just gives you the reverse of this graph, with the resistance starting to decrease slowly and then faster. The two terminal connection is non-polar; it looks the same however you hook it up. The only thing that changes is which end of the graph you start from.

I didn't understand it until I simmed it in Excel:

[PRR]

> I can get a clear shart 5K pot.  They don't make a 1K one!   

So make ALL resistors 5X larger.

Unless Q1 is real leaky, it will work.

[italianguy63]

Paul does that mean making the Level pot 2M5?  MC

[psychedelicfish]

Paul does that mean making the Level pot 2M5?  MC

The level pot's value shouldn't matter too much, as long as the RC circuit with the output cap has the same corner frequency.