I need to spread out a very small range on a potentiometer

[midwayfair]

I have a depth control with a 25K linear taper pot ...



With the 4.7K in parallel, that makes it a C taper pot of about 4K.

I also put a 10K across lugs 2 and 3 because otherwise about half of the knob's travel didn't really do much. So now my taper should have a really big jump early and a spread out upper portion, but it still isn't quite what I needed: There's a very small range around 10:00-10:30 on the knob that's very sensitive, going from "not doing anything" to "doing a lot." I'd like to spread out that specific range over a bigger portion of the pot's travel. Is there a good way to do that while still keeping the same minimum and maximum values?

If I could describe it better, it would start out as a C taper for the first few K, then become an audio taper for the rest of its travel.

EDIT: Hm, a 10KC might be working a little better ... I think I can live with that if there's not a way to do what I'm looking to do.

[peterg]

Jon. Not sure if this is a solution but the Tubesscreamer uses a G pot which has a unique taper. Might be a fix. Might not be but is the only non A B or C taper pot I know of.

[midwayfair]

Jon. Not sure if this is a solution but the Tubesscreamer uses a G pot which has a unique taper. Might be a fix. Might not be but is the only non A B or C taper pot I know of.

Is "G" different from a W taper?

I found a graph ... looks like it's the opposite of what I need.

http://electronics.stackexchange.com/questions/76313/does-anyone-have-a-g-pot-graph


Here it is ... the one in the middle
http://www.diystompboxes.com/smfforum/index.php?topic=70732.msg569687#msg569687

[PRR]

One thought is that the LEDs are part of the problem. They steal current from the collector load. If they were wired down from B+ instead of up from zero they could be part of the solution.

Pot loading is surely part of the problem. The LEDs+4K7 are a heavy load for any 50K pot. You really want ~~5K collector load. So make R8 a 5K pot.

A wider point: you probably want a steady DC in the LEDs plus a variable LFO AC. You might separate the two functions. LEDs resistor to a trimmer off B+. Another resistor and coupling cap to the depth wiper.

And I'm sorry, but the Rate leg doesn't go flying up in the sky. Maybe it could, but electrically all three C-R legs come together, at "GND".

[psychedelicfish]

I would have done it like this:

[midwayfair]

I would have done it like this:

The LEDs don't get brighter when the depth goes down like this. It actually doesn't vary the depth much, either.

The LEDs+4K7 are a heavy load for any 50K pot. You really want ~~5K collector load. So make R8 a 5K pot.

Thanks -- just did this and it's quite a bit better. I guess I was going the wrong way on the pot size by increasing it!

One thought is that the LEDs are part of the problem. They steal current from the collector load. If they were wired down from B+ instead of up from zero they could be part of the solution.

I tried every possible hookup I could think of and the only way to turn the LEDs on when the depth was turned down was to take them from the collector in some way to ground ... everything else makes them dim when the depth gets low.

A wider point: you probably want a steady DC in the LEDs plus a variable LFO AC. You might separate the two functions. LEDs resistor to a trimmer off B+. Another resistor and coupling cap to the depth wiper.

Okay, I tried this hookup. When I tried decoupling the LEDs in the past, it didn't occur to me that they needed a steady DC source (I kept ending up with them blinking for a second and the stopping.)

It does seem to be marginally better overall, but it takes a lot of dialing in for the two 10Ks and the idle pot. It does seem to have all the same sounds at the top of the dial, and the waveform is a little softer near the middle. But the LEDs are also dimmer.

I think the 5KC pot is the best I'm going to get with this setup ... once a trimpot and a few more resistors are added, there's probably no benefit in sticking with the transistor, since the op amp setup from the tremulus lune would be comparable parts-wise.

[davent]

An 'S' taper pot maybe?



The article;  http://sound.westhost.com/pots.htm#chg-law

[midwayfair]

An 'S' taper pot maybe?



The article;  http://sound.westhost.com/pots.htm#chg-law

That's the article I was trying to find. Thanks!