Keeping with the guitar FX theme, the easiest although possibly not the
best way to fix the scratchy pot is to use the gain setup from a fuzzface.
Instead of wiring the resonance pot as variable resistor wire the 2
outer lugs to the board. Then wire a large electolytic cap, I used 22uF,
between one of the outer lugs and the wiper. I put the + side towards
the NPN transister, but it seems to work either way. Here's quick
drawing of what I mean.
http://www.eskimo.plus.com/fxstuff/resonance_mod.png
This way as far as DC is concerned the pot is always set on full, so
turning it doesn't affect the DC gain of the circuit and because the cap
blocks DC you don't get any scratchy effect. The cap lets AC pass
through it so turning the pot alters the amount of AC gain.
hope this helps :)
Ken Johnston wrote:
Show quoted textHide quoted text
> Isn't the Synthacon res pot is like the boost control on the Dallas
> Rangemaster treble boosters for guitar? From the GEOFEX site, regarding
> this:
>
> "Another quirk of the original is that there is a DC voltage across the
> volume control, which also serves as the collector load resistor. This
> means that it will inevitably scratch and crackle whenever the control
> is moved even if you use high-collar conductive plastic pots. This was
> OK in the time of the original unit, as the designer assumed that a
> player would set up this thing and leave it, not twiddling the control
> during a number. There are ways to "correct" this, but they complicate
> the design unduly, so I have chosen to leave them out, going with the
> original circuit. It will crackle when you twist the "boost set"
> control."
