Southern Belle (or Mach 1) mod - less gain range?

M

m00ni

New member
Hi,
Since I can't really read schematics (yet), I may be asking something stupid here, but here goes anyways:

Can I mod my Southern belle (=Greer Southland) to have smaller gain range? I've noticed that with gain between 9-10 o'clock it provides a tighter/more focused alternative to my Greer Lightspeed in its higher gain settings. With these settings, the two aren't miles apart, but I've found uses for both. With the gain set low on both, they also work together quite nicely.

The Belle, however, has such a Hhuuge gain range that dialing in the right low/low-medium gain tone moment can take some time. That makes me wonder if it's possible possible to reduce the gain range that the pedal has? With the way it is now, the sweet spot is usually found between 9-10 and I can't imagine ever going beyond 11 or noon. (I think the higher gain settings don't sound too pleasant on this pedal.) Could this mod as simple or changing the 1M gain pot to, say, a 500k one? Or could I achieve the same effect by soldering a resistor to the pot or something? These two have been suggested as solutions to decreasing the gain range in other pedals, but if I've understood correctly, whether this works or not depends on the schematics of the pedal.

(I also have a Mach 1 pcb at hand as sort of backup for my Lightspeed. If you can suggest a mod that would tighten the Mach 1 / Lightspeed a bit, I'd be interested to hear about that, too. I understand those two pedals are more or less the same with only minor differences.)

Thanks for help. Really appreciate this community.
 
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R6 will set the minimum gain. Replacing the Drive pot is probably the simplest and most effective solution. A500k might be low enough, but on an audio-taper pot, you might want to go as low as 250k. Do you have a multimeter? If so, set Drive to the highest gain setting you'd ever want, then measure the resistance between lugs 1 and 2. That will tell you exactly the value pot you want.
 
Thanks, sounds simple enough! I need to give this a try.

Am I still correct in thinking that whether something like this works depends on the circuit in question? I vaguely remember reading something to this effect in a few places.
 
It will always depend on the circuit. Variable resistance to control gain is a pretty common approach, but it's not always implemented the same way. For example, you would need a larger value to get less gain in a Fuzz Face.
 
A while back I built a Kadundra (Vemuram Karen) with an A500K pot instead of the stock B1M, reduced the size of R4 (150K) to 33K ( the minimum gain resistor) and left the width trimpot off altogether. It turned it into a fantastic overdrive. I'm all for reducing the fizz in dirt pedals. Not really a metal player!
 
A quicker mod would just to be to add a resistor (such as 330k) across the drive pot (lug 1-2).

This will work in parallel with the pot resistance. (Max would be 1000k || 330k which equals 248k).

You could either do this as an experiment to determine your desired max, and then use a pot as the permanent mod. Or, keep the resistor as the permanent mod if you’re happy with the sweep.

Calculating parallel resistance is an easy formula, but I like to use this app. It also has an RC filter calculator.
 

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Yes, but it may or may not be disagreeable.

Here’s a graph roughly showing the sweep of a 250kA (blue) vs 1000kA + 330k in parallel (green)
 

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