converting a 5k pot to a 4.7k?

deadastronaut · February 23, 2011, 10:30:00 AM

can this be done..?

i just need to nip the last bit of range/turn off the 5k...so it will behave as a 4.7k...on a fussy speed control...

this is the problem in the uk..we have 4.7k's...the rest of the world has 5k's...for some reason..

ayayay! · February 23, 2011, 10:39:28 AM

I highly doubt you'll get your desired results, but you can try: http://www.diystompboxes.com/analogalchemy/emh/emh.html

nick d · February 23, 2011, 10:41:08 AM

I would say that 4.7K and 5K are the same if you consider the tolerance -
us in the UK just understand decimal points better !

deadastronaut · February 23, 2011, 10:44:06 AM

the tolerance is unreasonably bang on for a change..4.9x..

jefe · February 23, 2011, 10:44:26 AM

Yeah, have you actually tried measuring the max resistance of the pot? It may already be a 4.7k, lol.. (edit: nevermind, just read your post!)

That said, I think you can wire up a 300 ohm resistor in series with a 5k pot to get 4.7k, if I'm remembering that correctly.

jefe · February 23, 2011, 10:45:25 AM

double post

deadastronaut · February 23, 2011, 10:48:59 AM

yep , measured it..

ok i'll try the 300r..as it makes sense math wise...

that would be signal>300r>lug3 then right?...

ayayay! · February 23, 2011, 10:50:19 AM

Quote from: jefe on February 23, 2011, 10:44:26 AM
Yeah, have you actually tried measuring the max resistance of the pot? It may already be a 4.7k, lol.. (edit: nevermind, just read your post!)

That said, I think you can wire up a 300 ohm resistor in series with a 5k pot to get 4.7k, if I'm remembering that correctly.

Sorry Jefe, that's backwards.

That would make it a 5.3k. (You add series resistors and parallel caps.)

deadastronaut · February 23, 2011, 10:50:58 AM

hmmmmm yeah...

what if i stick the 300r on the lug2 out?..to outgoing signal?

ayayay! · February 23, 2011, 10:55:16 AM

This is a speed control? I'm sure you've checked this, but the taper is Linear right? Maybe try a reverse audio taper if the speed is all bunched at the end.

Another trick is a 10kB pot w/ a 9k across the outer lugs. That will get you uber close. Of course now you have to go find said parts... Okay so maybe a 8.2k across the outer lugs.

Gurner · February 23, 2011, 10:56:47 AM

Quote from: jefe on February 23, 2011, 10:44:26 AM
Yeah, have you actually tried measuring the max resistance of the pot? It may already be a 4.7k, lol.. (edit: nevermind, just read your post!)

That said, I think you can wire up a 300 ohm resistor in series with a 5k pot to get 4.7k, if I'm remembering that correctly.

You didn't remember correctly ;-)

Edit: Oops...just seen your follow up post!

To convert a 5k pot to a 4.7k pot, you need to wire a resistor in parallel across the two outer lugs . Assuming it's a linear pot, then to convert a 5k pot to 4.7k, needs an 80k resistor, I'm stupid & lazy to boot, so I lethargically use one of these calculators....

http://www.1728.com/resistrs.htm

jefe · February 23, 2011, 10:59:18 AM

Yeah, thanks for the correction guys.

deadastronaut · February 23, 2011, 10:59:57 AM

yep its linear... ok i'll try the 80 (82k ) across outer lugs now...cheers guys,..

deadastronaut · February 23, 2011, 11:02:07 AM

brilliant!... gurner wins the prize....i now have a 4.61 pot....yay!..

thanks so much!.. .....strange maths though!...

jefe · February 23, 2011, 11:06:51 AM

That's a cool trick, isn't it?

deadastronaut · February 23, 2011, 11:10:41 AM

yeah very cool...have to remember that one!....cheers guys!..

ayayay! · February 23, 2011, 01:14:09 PM

QuoteTo convert a 5k pot to a 4.7k pot, you need to wire a resistor in parallel across the two outer lugs . Assuming it's a linear pot, then to convert a 5k pot to 4.7k, needs an 80k resistor, I'm stupid & lazy to boot, so I lethargically use one of these calculators....

I thought of that too but I think you'll find the results you were wanting using my 10k pot trick above. However I also realize you are working with what you have. Carry on!

deadastronaut · February 23, 2011, 01:31:05 PM

yeah i get what you mean, would have been best to lower a 10k i guess, as thats the normal thing to do, just didnt wat to rip this apart after doing a neat-ish job on it

...thanks all..

LucifersTrip · February 23, 2011, 05:25:05 PM

Quote from: deadastronaut on February 23, 2011, 11:10:41 AM
yeah very cool...have to remember that one!....cheers guys!..

It is cool, but just note that the sweep will change.

It will make little difference in this case since the difference between 4.7 & 5 is relatively small.

But if you took a 100K pot and put a 100K resistor across the lugs to get 50K, it will not act the same as a 50K linear pot. The sweep will be milder at the beginning [ie, you'll hit 25K after turning half way] and then a sharper climb to 50K nearing the end of rotation...more heavily weighted to the upper end.

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converting a 5k pot to a 4.7k?