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

[tracer03]

Looking to get my build on soon, and I've added the Lovepedal Dragon (layout) , Foxrox CC Hybrid (layout) and the Carlsbro Fuzzbox (layout) to the build list.

Problem is - the Dragon and Foxrox state they need 500R Lin pots, and the Carlsbro layout shows a 25uf Axial Cap...I know I could *probably* get away with a 22u or 33u axial, but what value would be best?

And as far as the 500r Lin pots go - I could sub 1k, but is there a way to add a resistor to the pot to get it closer to the spec value?

Thanks in advance.

[nocentelli]

22u/25u/33u, you would struggle to tell the difference in a blind test.

For a 500r pot, wire a 1k resistor across lugs 1 and 3 of a 1k pot (or use a 1k reverse log pot.

[GrooveChampion]

How would using a 1k lin pot affect that? Out curiosity

[tracer03]

nocentelli wrote

For a 500r pot, wire a 1k resistor across lugs 1 and 3 of a 1k pot (or use a 1k reverse log pot.

Sorry, confused...if I use a 1K Rev Log Pot, would I still need to wire the 1k resistor, or just use as is?

[GrooveChampion]

If you wire the resistor you get closer to the 500R pot range needed, wiring lets say a 1K may cause the resistance at max to be bigger which can make the pedal sound weird or make it produce no sound at all, above a certain resistance level, theoretically. I am fairly certain you can get away with a 1k lin with no issues.

[nocentelli]

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

[tracer03]

Great explanation. Thanks for that!