Potentiometer help needed (limited shaft range)

[LiquidMetal]

Greetings!

Recently I was experimenting with guitar volume swells (the type you do with your pinky). It seems this will be much easier to achieve if the volume pot shaft range is not close to 360 degrees, but something between 90 and 180 degrees. I did some searches, but was able to find anyone manufacturing such pots. There are multi-turn pots, but nothing less than 300 degrees.

I was wondering if you know a company selling such a product or a way to modify a regular potentiometer to fit these requirements.

Thanks in advance

[digi2t]

Maybe use a resistor to steepen the taper of the pot?

Personally, I prefer a pedal over my pinky. I find it offers a greater degree of control.

[Kipper4]

Could you please ellaborate on the resistor to steepen the taper of the pot.
Where do you put the resistor?
What size resistor?
What effect does it have/ how does it work?

Thanks.
I'm here to learn

[nocentelli]

You want a log pot rather than a linear, so you majority of the decrease in resistance is in the last quarter or so of the pot's turn. However, most volume pots are already log, since the ear perceives sound increase in a non-linear manner (or something).

As for resistors, you can alter the taper (and value, which is inherent in this method) by placing a fixed resistor in parallel with the lugs of a pot - there are a few different ways, but as I recall they tend to create an anti-log type taper (unless, of course you wire the pot "backwards"). Much of this is covered in Geofex's "Secret life of pots", and you'll find more with a search for "taper resistors" or "resistor + pots + parallel" or something similar.

[gritz]

http://www.geofex.com/article_folders/potsecrets/potscret.htm

Plenty of goodness in there regarding using resistors to manipulate pot tapers. Unfortunately it does futz with the load that your guitar pickup sees. It's tricky - I'm not aware of any pots in the 180 degree range (that's not to say that there are none, obviously!). There are pots made especially for joysticks which go up to 60 degrees (I think), but they're linear and too low in value for the hacking mentioned in the above article.

Lateral thought - a volume knob of a smaller diameter would give you more degrees of rotation per inch of pinky.

[pinkjimiphoton]

you don't really want a log pot for volume swells tho. you need to be able to go from off to full.

my suggestion? try a bigger knob. the bigger the knob, the less you gotta turn it to get the full range of the pot. 

[joegagan]

bigger knob requires more physical movement to get the range. remember your ten speed bike?

i sanded the trace on my 250k tone pot to get the full swing in the first one - fourth rotation ( a little less than 90 degrees).

[armdnrdy]

Joe,

My god man!!

What haven't you modified!! 

[joegagan]

pretty sure nothing.

[LiquidMetal]

i sanded the trace on my 250k tone pot to get the full swing in the first one - fourth rotation ( a little less than 90 degrees).

Can you please share more details how to do the sanding?

[joegagan]

I started with a cts 24mm guitar pot, 250k. I forget which area i sanded, experiment. I used 600 emery paper.

[joegagan]

Gritz, digikey stocks 100k joystick pots , some even have switches built in. With some experimenting, one could possibly make a switchable 'swell' pot that only kicked in when manipulated , reverting to the standard vol pot when not in use. ?

[maartendh]

For 180 degrees rotation, use a pot twice the original value (ohms); for 90 degress you use 4 times the original value (lineair). This will give you the range of the former pot while using only a part of the rotation - you simply never turn the pot to a resistance higher than that of the original pot.

So the original pot is e.g. 100k (that is: from 0 to 100 k over 360 degrees), when you replace it by a 500k it wil give you 0 - 100k over approximately 90 degrees.
I do this with wha rocker pedals and it works well.

Maarten

[joegagan]

That is a clever solution, but i have found the tone of that approach to be less than satisfactory both as volume control and especially in inductor type wah circuits.

[Kipper4]

great stuff guys some good solutions here and thanks for the article.

[duck_arse]

dual-gang balance pots from stereo amps. don't they have dead bands either side of 12 o'clock?