Re: Part substitutions/mods for hard-to-find values?

Posted by nocentelli on Oct 04, 2017; 3:57pm
URL: http://guitar-fx-layouts.238.s1.nabble.com/Part-substitutions-mods-for-hard-to-find-values-tp40149p40158.html

A fuzzface usually has a 1k fuzz pot which sets the bias (lug1 to ground, lug 3 to emitter) AND allows gain control by connecting a 25u cap between lug 2 and ground: This allows AC voltage to pass from the emitter to ground, increasing the gain of Q2 as the pot is turned up and resistance between lug 2 and 3 is reduced from 1kohm (minimum gain) to zero ohms (max gain). The resistance between lug1 and 3 stays static at 1k. This has the pot working as a potential divider.

In the Lovepedal dragon, the 1k pot is simply swapped for a 500r pot (as a potential divider) and a bias trimmer exists on the collector to get the transistor into the appropriate bias. You could theoretically use a 500r, 1k or 2k and you could compensate with the trimmer to get (e.g.) the mythical 4.5 volts on the collector.


HOWEVER In the Foxrox CC version of the fuzzface, the standard fuzzface 1k pot is replaced by a fixed 1k resistor for bias, and a 500 ohm pot for gain control: The pot only has two lugs connected (since the 1k fixed resistor is handling the bias) and a 500ohm was probably chosen because the first half turn of a linear 1k pot on a standard fuzzface doesn't do much, the interesting fuzz textures are all in the 500 ohm-to-zero range. A 500ohm pot spreads these sounds out across the whole travel of the pot. A 1k pot with 1k across the outer lugs gives you a parallel resistance equal to 500ohms, replicating the pot - it will also alter the taper slightly, but in a good way.

If you chose a 1k reverse log pot, the useless region from 1k down to 500r is bunched up at the start of the pot's travel and the 500 to zero ohm is spread over a much wider region of the pot's travel  (11 o'clock to five o'clock).

TL:DR - No, a 1k rev log does not need a parallel resistor across the lugs for the Foxrox. A 1k with a parallel resistor will give a similar "feel". The Lovepedal dragon could use a 1k pot alone, or a 1k with 1k in parallel makes no odds since you'll have to set the bias manually anyway