Changing pot values

[salviablue]

This may seem like a daft question but lets say you where a total skin flint or miser and you needed pots of a certain value for a project. Now in your bit box there are loads of pots of values like 5K, 10K, 100K and 500K and you need a 200K and a 250K pots. Would one be able to change the value of the pots in ones bit box to the required values. How could i hook up these pots with out doubling them up? I would like to just use resistors to change values if pos.?
Cheers.

 

[Nigel Goodwin]

It depends entirely on what the pots are being used for - some times you may be able to change the circuit to use a different value, some times you can't, other times you may be able to just drop a different value in with no changes.

 

[philba]

If you are asking if you can modify the pots themselves - no, you can't.

ask nigel said, you may be able to modify the circuit or just use a different value pot. If your pot is used for a voltage divider, it may well be ok but watch input impedence. For example as a simple voltage reference input to a comparator or opamp where the two sides of the pot are tied to the rails, twice or 1/2 the value will probably be fine.

In general, though, you really need to understand what the pot is used for in the circuit.

 

[salviablue]

Its for a phasor effects unit, here is the diagram. (Its the original one)
https://www.electro-tech-online.com/custompdfs/2006/11/p90ramp.pdf
Its the BIAS and MIX POTs i dont have. What i do have are loads of resistors, 500K pots, 100K pots and 10K pots. I am a begginer and therefore have limited knowledge.
I was wondering whether i could replace the 200K pot with a 100K pot and change the two resistors at the side pins to around 73K each?
And could i replace the 250K pot with a 500K pot with a 500K resistor in parallel?
Any help would be fantastic, Cheers

 

[Hero999]

"No posting from other web sites."
Naughty, naughty. I don't think you're supposed to post this here. Linking is alright but not posting as it's breach of copyright.

 

[salviablue]

"No posting from other web sites."
Naughty, naughty. I don't think you're supposed to post this here. Linking is alright but not posting as it's breach of copyright.

Opps! Cheers, i have removed the possible law suit! Replaced it with a link instead.

Anyway, would connecting the two outer pins (1+3) with a 500K resistor on a 500K pot make it a 250K and how low would the resistance go? Would it be better to connect a 250K resistor between 1+2, and a 250K resistor between 2+3?

Further would a dual pot (one with two pots on one spindle) thats 100K make one 200K pot if pin 1 on one pot was connected to pin 3 on the other pot with both pins 2 tied together (with the free pins 1+3 AND PIN 2 CONNECTED INTO THE CIRCUIT)?
aNY HELP WOULD BE MOST GRATEFULLY APPRECIATED.

 

[salviablue]

"No posting from other web sites."
Naughty, naughty. I don't think you're supposed to post this here. Linking is alright but not posting as it's breach of copyright.

Opps! Cheers, i have removed the possible law suit! Replaced it with a link instead.

Anyway, would connecting the two outer pins (1+3) with a 500K resistor on a 500K pot make it a 250K and how low would the resistance go? Would it be better to connect a 250K resistor between 1+2, and a 250K resistor between 2+3?

Further would a dual pot (one with two pots on one spindle) thats 100K make one 200K pot if pin 1 on one pot was connected to pin 3 on the other pot with both pins 2 tied together (with the free pins 1+3 AND PIN 2 CONNECTED INTO THE CIRCUIT)?
aNY HELP WOULD BE MOST GRATEFULLY APPRECIATED.

 

[fingaz]

This seems like a lot of effort to save a quid. . . you can get pots for pence each from any number of web sites. . .

www.bowood-electronics.co.uk or www.rshelectronics.co.uk

 

[salviablue]

Pots

Cheers but neither of those places you mentioned have either 200K or 250K pots! I cant find anywhere on ebay thats supplies what im after either, and with my limited knowledge was wondering as to whether there was any way around buying in these pots i cant find. There are no electronic stores within 20 miles of me and i can only usually pay by cash or paypal so that is why i could do with a work around. Infact i get most of my parts through ebay or salvaged equipment and if i cant find the part im stuck with out an alternative. Although i am learning all the time i dont know whether i would be able to make satisfactory work arounds on my own.
Cheers

 

[Nigel Goodwin]

Cheers but neither of those places you mentioned have either 200K or 250K pots!

The tolerence on pots is usally +/-20% - 200 and 250 aren't preferred values, but 220K is a standard value - 200/220/250 are all near enough the same for pots.

Try

 

[salviablue]

pots

Thankyou very much, just the kind of info i needed, and thanks for the link aswell!

One last thing am i correct with the assumption made about turning a 100K double pot into a 200K single pot?
Thanks all for the info, Cheers.

 

[Nigel Goodwin]

One last thing am i correct with the assumption made about turning a 100K double pot into a 200K single pot?

No, you can't turn a 100K dual pot into a 200K single - although you can turn a 200K dual into a 100K single (just parallel them together).