can i make a concentric 1 meg dual pot...

[pinkjimiphoton]

from a stacked, concentric 500k one? i want to build a project into a wah shell, it needs two 1 meg pots, but i can't seem to find that config so far.

i CAN find 500k, tho. i know  i can add resistors to the 500k pots to get them down in resistance, but is there any way to increase them?

any ideas?

thanks guys!

[R.G.]

i CAN find 500k, tho. i know  i can add resistors to the 500k pots to get them down in resistance, but is there any way to increase them?

Not and have them still cover the full 1M range, no.

You'd have to put resistance in series with them, and that could get you up to 1M max, but it would also mean the combination was 500K to 1M, not 0 to 1M.

If you could get a 500K QUAD dual concentric pot, you could put them in pairs in series and get 0-1M. The "concentric" thing is getting you.

I would wonder whether the circuit really needed 1M, or if I could modify it to work with 500Ks I could get, if it were me.

[Taylor]

Are you sure concentric is what you need? Concentric means that the two knobs can be adjusted separately, but they are stacked on top of each other, like this.

Since you mention a wah pot, I'm guessing you want your wah treadle to sweep them simultaneously. That would be a "dual-gang" pot rather than concentric. You might have luck here as (as RG alluded) you can with some surgery remove the resistance wafers in these pots and replace them with 1m ones from single pots. Not an easy thing to do, however.

Can you tell us what the circuit is? As RG says it could probably be modified so that 500k would be a usable value, or it might even be usable already.

[digi2t]

Hey bro,

Did some more research. Check out OMEG http://www.omeg.co.uk/products.htm

http://www.omeg.co.uk/p20typ1.htm

and the request for quote/order form is here; http://www.omeg.co.uk/p2c2owb2.htm

[pinkjimiphoton]

i CAN find 500k, tho. i know  i can add resistors to the 500k pots to get them down in resistance, but is there any way to increase them?

Not and have them still cover the full 1M range, no.

You'd have to put resistance in series with them, and that could get you up to 1M max, but it would also mean the combination was 500K to 1M, not 0 to 1M.

If you could get a 500K QUAD dual concentric pot, you could put them in pairs in series and get 0-1M. The "concentric" thing is getting you.

I would wonder whether the circuit really needed 1M, or if I could modify it to work with 500Ks I could get, if it were me.

i'm wondering if i'd get enough sweep, too...but dino called me last nite and gave me some good leads, so hopefully that will pan out. i can fit a dual pot in, but a quad would be too thick i'm afraid.  right now i'm waiting on a quote from these chaps in big blighty, they seem to have everything!!  so i'm keeping my eyes crossed!!

[MikeH]

Without getting too far off topic, I've wondered something about this when I wanted a dual ganged pot with 2 different values.  I couldn't find one anywhere with the values I was looking for, I eventually ended up using all kinds of parallel resistors to get the values I needed and it worked ok, but I wondered if I could take another pot of the same diameter, and swap out the resistive element  from one to the other.  So if I wanted a 1M/1K, I would take a dual 1M, and swap out one of the gangs with the inards of a 1K pot.  never tried it though.

[pinkjimiphoton]

Are you sure concentric is what you need? Concentric means that the two knobs can be adjusted separately, but they are stacked on top of each other, like this.

Since you mention a wah pot, I'm guessing you want your wah treadle to sweep them simultaneously. That would be a "dual-gang" pot rather than concentric. You might have luck here as (as RG alluded) you can with some surgery remove the resistance wafers in these pots and replace them with 1m ones from single pots. Not an easy thing to do, however.

Can you tell us what the circuit is? As RG says it could probably be modified so that 500k would be a usable value, or it might even be usable already.

hi taylor,
i thought about doing pot surgery already, but it could be a lot of work just to screw it up. the reason i need dual concentric is for a pair of resonance controls, not the wah sweep pot. i wanna build this thing into a crybaby shell...it'll be tight with 4 pots  and the treadle pot, but i think i can do it if i can use the concentric one.

here's the schematic...i don't know enough yet to be able to tell if 500k would be enough to pull it off:

[pinkjimiphoton]

Hey bro,

Did some more research. Check out OMEG http://www.omeg.co.uk/products.htm

http://www.omeg.co.uk/p20typ1.htm

and the request for quote/order form is here; http://www.omeg.co.uk/p2c2owb2.htm

hi dino, i contacted them last nite, hopefully they can hook me up...waiting for a reply!! thanks bro!!

[pinkjimiphoton]

heard back from them....holy sh**!!

Jimi:

            At 3 pieces you are looking at $62.02 each + $50.00 set-up charge. Lead time is 2 weeks.



Tom

[slacker]

500k should work fine in there, the resonance goes down as resistance goes up so the worst that can happen is minimum resonance will won't be as low.

[Mark Hammer]

How much continuous control and how much matching do you need?

In the audio world, one of the regular solutions to the problem of having matched potentiometers is to use a multi-step rotary switch.  For example, a high-end preamp, designed to provide perfectly matched channel volume adjustment, might have a 40-step rotary switch.  So, consider a virtual pot, made out of a resistor "ladder" that adds up to 1meg, but comprised of multiple 1% resistors in series.  The wiper of our virtual pot simply selects which junction it is tapping.

The 40-step units are understandably quite pricey, but there are very inexpensive 6-step switches available.  If you really don't need more than 6 levels of resolution for what yu're trying to control, why not try a rotary switch?

[pinkjimiphoton]

no idea, mark.
i don't think they have to be matched or anything. easiest thing to implement your suggestion may be to just breadboard it and use a couple pots, take some readings where it sounds "good" and indeed use rotary switches.

but if the resonance won't be affected too much, it's easier and quicker to just use a readily available dual stacked concentric 500 k pot, and if i have to, add some resistance on whatever end seems to need it i guess.

thanks for all the great advice guys! much appreciated!!