Decrease ohm on potentiometer

I needed a 50k linear pot today, but didn't have any at home. So I thought I would try to decrease a 470k pot with a resistor. I used a 56k resistor between the outer pins of the pot. When I measure the outer pins I get 50k as expected. But when I measure outer pin to inner pin while switching the pot, then the resistance starts at 0, then goes up to over 100k in the middle and then down to 50k when all the way up (or reverse between inner an the other outer). This can't be right?

You might need to add two resistors, from each end to the wiper. It's just a hunch, and i couldn't tell you what values, but maybe two 56k's would be a starting point?

joakimkarlthomas said:

I needed a 50k linear pot today, but didn't have any at home. So I thought I would try to decrease a 470k pot with a resistor. I used a 56k resistor between the outer pins of the pot. When I measure the outer pins I get 50k as expected. But when I measure outer pin to inner pin while switching the pot, then the resistance starts at 0, then goes up to over 100k in the middle and then down to 50k when all the way up (or reverse between inner an the other outer). This can't be right?

Click to expand...

Slugging pots are generally done to change the taper (with mixed success). Trying to change the overall resistance with a parallel resistor will only work for that single measurement, inside it will still be the old value.

JR

put the 56k between gnd lug and wiper, not across pot

500K audio taper will work better if you have it

joakimkarlthomas said:

I needed a 50k linear pot today, but didn't have any at home. So I thought I would try to decrease a 470k pot with a resistor. I used a 56k resistor between the outer pins of the pot. When I measure the outer pins I get 50k as expected. But when I measure outer pin to inner pin while switching the pot, then the resistance starts at 0, then goes up to over 100k in the middle and then down to 50k when all the way up (or reverse between inner an the other outer). This can't be right?

Click to expand...

Check
https://groupdiy.com/index.php?topic=67399.msg856620#msg856620

I haven't researched but was curious after reading this thread.

Does using a pot like a rheostat (actually....lug and wiper tied, other lug  in series with another resistor to ground), change the taper?

http://sound.whsites.net/pots.htm#chg-law

scott2000 said:

I haven't researched but was curious after reading this thread.

Does using a pot like a rheostat (actually....lug and wiper tied, other lug  in series with another resistor to ground), change the taper?

Click to expand...

Khron said:

http://sound.whsites.net/pots.htm#chg-law

Click to expand...

Thanks! I've seen that article in the past. I'm still unclear . This article does show that adding resistance in parallel as a variable resistance set up does change the taper but doesn't mention anything about using the pot as a variable resistor with series resistor to make a range of resistance. Like if the op used his 470k pot as a variable resistor with his 56k resistor in series, he'd have a pot that worked from 56k to 526k...... I was unsure if this type of set up changes the taper.

Not a big deal to me, I was just curious.

scott2000 said:

I haven't researched but was curious after reading this thread.

Does using a pot like a rheostat (actually....lug and wiper tied, other lug  in series with another resistor to ground), change the taper?

Click to expand...

Yes it does, but generally not in a satisfactory way. If you look at the other thread, you will see why.

Wow.....

Finicky little guys....

scott2000 said:

Wow.....

Finicky little guys....

Click to expand...

I tried a search and didn't have much luck but we discussed this here many times over the years.

JR

Don't believe what you read on the interwebs.

Get a pot. Mount a knob and numberplate. Find your ohm meter. Plot the Ohms for various numbers in various connections.

The truth is out there. But you have to look at it.

CJ said:

put the 56k between gnd lug and wiper, not across pot

500K audio taper will work better if you have it

Click to expand...

It worked perfectly. Thanks!

joakimkarlthomas said:

It worked perfectly. Thanks!

Click to expand...

The question there is why did you need a 50k pot in the first time? By loading a 500k pot with a 56k resistor, the taper (divider ratio variation vs. rotation) is very significantly altered, making it equivalent to a 50k Log pot (assuming the 500k pot is Lin). Was it what you needed?
Or is your 500k pot already a Log (or audio)? In that case the taper is a retarded Log, which may be impractical in operation, with a very sudden level jump at the end of rotation.