JonnyAngle wrote:I'll take up your offer on a diagram RMA

Evan, it's just a variable resistor from 9v to 0v

Okay, Fig 1 depicts what you've got with the limited useful window of rotation. The upper point and lower point of rotation will have to be direct measured for the voltages that apply to your unit, I've just tossed a couple numbers there that are meaningless beyond the example.

So, first thing to do is determine the percentage of important voltages (in this case 6.8 is JUST BEFORE you start to observe the starved effect, and 3 is when the circuit falls flat), and know your supply voltage.

Supply voltage is 9.0, so 0.09 is one percent.

6.8 divided by 0.09 is roughly 75.56%.

3 volts is 33.33%

Now you need to know the size of the pot, again 10K is just a conjured number, and the percentage of range that pot will fill:

10K needs to fill in the blank between 75.6 and 33.3%; therefore 10K = 42.3% (75.6 minus 33.3), and the over all branch resistance needs to be roughly 23640 ohms (10K divided by .423, or 42 some odd percent), sandwiched between 33.3% of nine volts at the low end, and 75.6% of nine volts at the high end.

One percent of 23640 ohms is 236.4 ohms.

Therefore 33.3 x 236.4 will give you the low resistor (7872 ohms) and 24.4% (the difference up top) turns into 5768 ohms.

The eagle eyes amongst you will pick up the discrepancy between what I just typed and what I originally drew, that ten ohm disparity is there because I started rounded my math at a different point, and none of this is critical because all these numbers can be shoved through a 5-10% tolerance (and rounding up/down to the nearest reasonable value, like 8K1 and 5K6).

Conversely, you can just figure it's good in roughly the center third of the turn and sandwich the 10K between two other 10K resistors and be in the ballpark.

For trim pots, just swap out the resistors for a trim pot with the wiper connected to one of the outer legs and forget the math (resistors are neater and cheaper though).

Did I clarify or crash the plane into the mountain?